- 30 Mar, 2020 13 commits
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John Fastabend authored
do_refine_retval_range() is called to refine return values from specified helpers, probe_read_str and get_stack at the moment, the reasoning is because both have a max value as part of their input arguments and because the helper ensure the return value will not be larger than this we can set smax values of the return register, r0. However, the return value is a signed integer so setting umax is incorrect It leads to further confusion when the do_refine_retval_range() then calls, __reg_deduce_bounds() which will see a umax value as meaning the value is unsigned and then assuming it is unsigned set the smin = umin which in this case results in 'smin = 0' and an 'smax = X' where X is the input argument from the helper call. Here are the comments from _reg_deduce_bounds() on why this would be safe to do. /* Learn sign from unsigned bounds. Signed bounds cross the sign * boundary, so we must be careful. */ if ((s64)reg->umax_value >= 0) { /* Positive. We can't learn anything from the smin, but smax * is positive, hence safe. */ reg->smin_value = reg->umin_value; reg->smax_value = reg->umax_value = min_t(u64, reg->smax_value, reg->umax_value); But now we incorrectly have a return value with type int with the signed bounds (0,X). Suppose the return value is negative, which is possible the we have the verifier and reality out of sync. Among other things this may result in any error handling code being falsely detected as dead-code and removed. For instance the example below shows using bpf_probe_read_str() causes the error path to be identified as dead code and removed. >From the 'llvm-object -S' dump, r2 = 100 call 45 if r0 s< 0 goto +4 r4 = *(u32 *)(r7 + 0) But from dump xlate (b7) r2 = 100 (85) call bpf_probe_read_compat_str#-96768 (61) r4 = *(u32 *)(r7 +0) <-- dropped if goto Due to verifier state after call being R0=inv(id=0,umax_value=100,var_off=(0x0; 0x7f)) To fix omit setting the umax value because its not safe. The only actual bounds we know is the smax. This results in the correct bounds (SMIN, X) where X is the max length from the helper. After this the new verifier state looks like the following after call 45. R0=inv(id=0,smax_value=100) Then xlated version no longer removed dead code giving the expected result, (b7) r2 = 100 (85) call bpf_probe_read_compat_str#-96768 (c5) if r0 s< 0x0 goto pc+4 (61) r4 = *(u32 *)(r7 +0) Note, bpf_probe_read_* calls are root only so we wont hit this case with non-root bpf users. v3: comment had some documentation about meta set to null case which is not relevant here and confusing to include in the comment. v2 note: In original version we set msize_smax_value from check_func_arg() and propagated this into smax of retval. The logic was smax is the bound on the retval we set and because the type in the helper is ARG_CONST_SIZE we know that the reg is a positive tnum_const() so umax=smax. Alexei pointed out though this is a bit odd to read because the register in check_func_arg() has a C type of u32 and the umax bound would be the normally relavent bound here. Pulling in extra knowledge about future checks makes reading the code a bit tricky. Further having a signed meta data that can only ever be positive is also a bit odd. So dropped the msize_smax_value metadata and made it a u64 msize_max_value to indicate its unsigned. And additionally save bound from umax value in check_arg_funcs which is the same as smax due to as noted above tnumx_cont and negative check but reads better. By my analysis nothing functionally changes in v2 but it does get easier to read so that is win. Fixes: 849fa506 ("bpf/verifier: refine retval R0 state for bpf_get_stack helper") Signed-off-by:John Fastabend <john.fastabend@gmail.com> Signed-off-by:
Alexei Starovoitov <ast@kernel.org> Link: https://lore.kernel.org/bpf/158560417900.10843.14351995140624628941.stgit@john-Precision-5820-Tower
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KP Singh authored
LSM and tracing programs share their helpers with bpf_tracing_func_proto which is only defined (in bpf_trace.c) when BPF_EVENTS is enabled. Instead of adding __weak symbol, make BPF_LSM depend on BPF_EVENTS so that both tracing and LSM programs can actually share helpers. Fixes: fc611f47 ("bpf: Introduce BPF_PROG_TYPE_LSM") Reported-by:
Randy Dunlap <rdunlap@infradead.org> Signed-off-by:
KP Singh <kpsingh@google.com> Signed-off-by:
Daniel Borkmann <daniel@iogearbox.net> Link: https://lore.kernel.org/bpf/20200330204059.13024-1-kpsingh@chromium.org
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Alexei Starovoitov authored
Joe Stringer says: ==================== Introduce a new helper that allows assigning a previously-found socket to the skb as the packet is received towards the stack, to cause the stack to guide the packet towards that socket subject to local routing configuration. The intention is to support TProxy use cases more directly from eBPF programs attached at TC ingress, to simplify and streamline Linux stack configuration in scale environments with Cilium. Normally in ip{,6}_rcv_core(), the skb will be orphaned, dropping any existing socket reference associated with the skb. Existing tproxy implementations in netfilter get around this restriction by running the tproxy logic after ip_rcv_core() in the PREROUTING table. However, this is not an option for TC-based logic (including eBPF programs attached at TC ingress). This series introduces the BPF helper bpf_sk_assign() to associate the socket with the skb on the ingress path as the packet is passed up the stack. The initial patch in the series simply takes a reference on the socket to ensure safety, but later patches relax this for listen sockets. To ensure delivery to the relevant socket, we still consult the routing table, for full examples of how to configure see the tests in patch #5; the simplest form of the route would look like this: $ ip route add local default dev lo This series is laid out as follows: * Patch 1 extends the eBPF API to add sk_assign() and defines a new socket free function to allow the later paths to understand when the socket associated with the skb should be kept through receive. * Patches 2-3 optimize the receive path to avoid taking a reference on listener sockets during receive. * Patches 4-5 extends the selftests with examples of the new functionality and validation of correct behaviour. Changes since v4: * Fix build with CONFIG_INET disabled * Rebase Changes since v3: * Use sock_gen_put() directly instead of sock_edemux() from sock_pfree() * Commit message wording fixups * Add acks from Martin, Lorenz * Rebase Changes since v2: * Add selftests for UDP socket redirection * Drop the early demux optimization patch (defer for more testing) * Fix check for orphaning after TC act return * Tidy up the tests to clean up properly and be less noisy. Changes since v1: * Replace the metadata_dst approach with using the skb->destructor to determine whether the socket has been prefetched. This is much simpler. * Avoid taking a reference on listener sockets during receive * Restrict assigning sockets across namespaces * Restrict assigning SO_REUSEPORT sockets * Fix cookie usage for socket dst check * Rebase the tests against test_progs infrastructure * Tidy up commit messages ==================== Signed-off-by: -
Joe Stringer authored
Add support for testing UDP sk_assign to the existing tests. Signed-off-by:
Joe Stringer <joe@wand.net.nz> Signed-off-by:
Lorenz Bauer <lmb@cloudflare.com> Acked-by:
Martin KaFai Lau <kafai@fb.com> Link: https://lore.kernel.org/bpf/20200329225342.16317-6-joe@wand.net.nz
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Lorenz Bauer authored
Attach a tc direct-action classifier to lo in a fresh network namespace, and rewrite all connection attempts to localhost:4321 to localhost:1234 (for port tests) and connections to unreachable IPv4/IPv6 IPs to the local socket (for address tests). Includes implementations for both TCP and UDP. Keep in mind that both client to server and server to client traffic passes the classifier. Signed-off-by:
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Joe Stringer authored
Avoid taking a reference on listen sockets by checking the socket type in the sk_assign and in the corresponding skb_steal_sock() code in the the transport layer, and by ensuring that the prefetch free (sock_pfree) function uses the same logic to check whether the socket is refcounted. Suggested-by:
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Joe Stringer authored
Refactor the UDP/TCP handlers slightly to allow skb_steal_sock() to make the determination of whether the socket is reference counted in the case where it is prefetched by earlier logic such as early_demux. Signed-off-by:
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Joe Stringer authored
Add support for TPROXY via a new bpf helper, bpf_sk_assign(). This helper requires the BPF program to discover the socket via a call to bpf_sk*_lookup_*(), then pass this socket to the new helper. The helper takes its own reference to the socket in addition to any existing reference that may or may not currently be obtained for the duration of BPF processing. For the destination socket to receive the traffic, the traffic must be routed towards that socket via local route. The simplest example route is below, but in practice you may want to route traffic more narrowly (eg by CIDR): $ ip route add local default dev lo This patch avoids trying to introduce an extra bit into the skb->sk, as that would require more invasive changes to all code interacting with the socket to ensure that the bit is handled correctly, such as all error-handling cases along the path from the helper in BPF through to the orphan path in the input. Instead, we opt to use the destructor variable to switch on the prefetch of the socket. Signed-off-by:
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Daniel Borkmann authored
We've added John Fastabend to our weekly BPF patch review rotation over last months now where he provided excellent and timely feedback on BPF patches. Therefore, add him to the BPF core reviewer team to the MAINTAINERS file to reflect that. Signed-off-by:
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KP Singh authored
The bounds checking for the arguments accessed in the BPF program breaks when the expected_attach_type is not BPF_TRACE_FEXIT, BPF_LSM_MAC or BPF_MODIFY_RETURN resulting in no check being done for the default case (the programs which do not receive the return value of the attached function in its arguments) when the index of the argument being accessed is equal to the number of arguments (nr_args). This was a result of a misplaced "else if" block introduced by the Commit 6ba43b76 ("bpf: Attachment verification for BPF_MODIFY_RETURN") Fixes: 6ba43b76 ("bpf: Attachment verification for BPF_MODIFY_RETURN") Reported-by:
Jann Horn <jannh@google.com> Signed-off-by:
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Jann Horn authored
reg_set_min_max_inv() contains exactly the same logic as reg_set_min_max(), just flipped around. While this makes sense in a cBPF verifier (where ALU operations are not symmetric), it does not make sense for eBPF. Replace reg_set_min_max_inv() with a helper that flips the opcode around, then lets reg_set_min_max() do the complicated work. Signed-off-by:
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Jann Horn authored
The BPF verifier tried to track values based on 32-bit comparisons by (ab)using the tnum state via 581738a6 ("bpf: Provide better register bounds after jmp32 instructions"). The idea is that after a check like this: if ((u32)r0 > 3) exit We can't meaningfully constrain the arithmetic-range-based tracking, but we can update the tnum state to (value=0,mask=0xffff'ffff'0000'0003). However, the implementation from 581738a6 didn't compute the tnum constraint based on the fixed operand, but instead derives it from the arithmetic-range-based tracking. This means that after the following sequence of operations: if (r0 >= 0x1'0000'0001) exit if ((u32)r0 > 7) exit The verifier assumed that the lower half of r0 is in the range (0, 0) and apply the tnum constraint (value=0,mask=0xffff'ffff'0000'0000) thus causing the overall tnum to be (value=0,mask=0x1'0000'0000), which was incorrect. Provide a fixed implementation. Fixes: 581738a6 ("bpf: Provide better register bounds after jmp32 instructions") Signed-off-by:
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Daniel Borkmann authored
Anatoly has been fuzzing with kBdysch harness and reported a hang in one of the outcomes: 0: (b7) r0 = 808464432 1: (7f) r0 >>= r0 2: (14) w0 -= 808464432 3: (07) r0 += 808464432 4: (b7) r1 = 808464432 5: (de) if w1 s<= w0 goto pc+0 R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x30303020;0x10000001f)) R1_w=invP808464432 R10=fp0 6: (07) r0 += -2144337872 7: (14) w0 -= -1607454672 8: (25) if r0 > 0x30303030 goto pc+0 R0_w=invP(id=0,umin_value=271581184,umax_value=271581311,var_off=(0x10300000;0x7f)) R1_w=invP808464432 R10=fp0 9: (76) if w0 s>= 0x303030 goto pc+2 12: (95) exit from 8 to 9: safe from 5 to 6: R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x30303020;0x10000001f)) R1_w=invP808464432 R10=fp0 6: (07) r0 += -2144337872 7: (14) w0 -= -1607454672 8: (25) if r0 > 0x30303030 goto pc+0 R0_w=invP(id=0,umin_value=271581184,umax_value=271581311,var_off=(0x10300000;0x7f)) R1_w=invP808464432 R10=fp0 9: safe from 8 to 9: safe verification time 589 usec stack depth 0 processed 17 insns (limit 1000000) [...] The underlying program was xlated as follows: # bpftool p d x i 9 0: (b7) r0 = 808464432 1: (7f) r0 >>= r0 2: (14) w0 -= 808464432 3: (07) r0 += 808464432 4: (b7) r1 = 808464432 5: (de) if w1 s<= w0 goto pc+0 6: (07) r0 += -2144337872 7: (14) w0 -= -1607454672 8: (25) if r0 > 0x30303030 goto pc+0 9: (76) if w0 s>= 0x303030 goto pc+2 10: (05) goto pc-1 11: (05) goto pc-1 12: (95) exit The verifier rewrote original instructions it recognized as dead code with 'goto pc-1', but reality differs from verifier simulation in that we're actually able to trigger a hang due to hitting the 'goto pc-1' instructions. Taking different examples to make the issue more obvious: in this example we're probing bounds on a completely unknown scalar variable in r1: [...] 5: R0_w=inv1 R1_w=inv(id=0) R10=fp0 5: (18) r2 = 0x4000000000 7: R0_w=inv1 R1_w=inv(id=0) R2_w=inv274877906944 R10=fp0 7: (18) r3 = 0x2000000000 9: R0_w=inv1 R1_w=inv(id=0) R2_w=inv274877906944 R3_w=inv137438953472 R10=fp0 9: (18) r4 = 0x400 11: R0_w=inv1 R1_w=inv(id=0) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R10=fp0 11: (18) r5 = 0x200 13: R0_w=inv1 R1_w=inv(id=0) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R5_w=inv512 R10=fp0 13: (2d) if r1 > r2 goto pc+4 R0_w=inv1 R1_w=inv(id=0,umax_value=274877906944,var_off=(0x0; 0x7fffffffff)) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R5_w=inv512 R10=fp0 14: R0_w=inv1 R1_w=inv(id=0,umax_value=274877906944,var_off=(0x0; 0x7fffffffff)) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R5_w=inv512 R10=fp0 14: (ad) if r1 < r3 goto pc+3 R0_w=inv1 R1_w=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7fffffffff)) R2_w=inv274877906944 R3_w=inv137438953472 R4_w=inv1024 R5_w=inv512 R10=fp0 15: R0=inv1 R1=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7fffffffff)) R2=inv274877906944 R3=inv137438953472 R4=inv1024 R5=inv512 R10=fp0 15: (2e) if w1 > w4 goto pc+2 R0=inv1 R1=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7f00000000)) R2=inv274877906944 R3=inv137438953472 R4=inv1024 R5=inv512 R10=fp0 16: R0=inv1 R1=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7f00000000)) R2=inv274877906944 R3=inv137438953472 R4=inv1024 R5=inv512 R10=fp0 16: (ae) if w1 < w5 goto pc+1 R0=inv1 R1=inv(id=0,umin_value=137438953472,umax_value=274877906944,var_off=(0x0; 0x7f00000000)) R2=inv274877906944 R3=inv137438953472 R4=inv1024 R5=inv512 R10=fp0 [...] We're first probing lower/upper bounds via jmp64, later we do a similar check via jmp32 and examine the resulting var_off there. After fall-through in insn 14, we get the following bounded r1 with 0x7fffffffff unknown marked bits in the variable section. Thus, after knowing r1 <= 0x4000000000 and r1 >= 0x2000000000: max: 0b100000000000000000000000000000000000000 / 0x4000000000 var: 0b111111111111111111111111111111111111111 / 0x7fffffffff min: 0b010000000000000000000000000000000000000 / 0x2000000000 Now, in insn 15 and 16, we perform a similar probe with lower/upper bounds in jmp32. Thus, after knowing r1 <= 0x4000000000 and r1 >= 0x2000000000 and w1 <= 0x400 and w1 >= 0x200: max: 0b100000000000000000000000000000000000000 / 0x4000000000 var: 0b111111100000000000000000000000000000000 / 0x7f00000000 min: 0b010000000000000000000000000000000000000 / 0x2000000000 The lower/upper bounds haven't changed since they have high bits set in u64 space and the jmp32 tests can only refine bounds in the low bits. However, for the var part the expectation would have been 0x7f000007ff or something less precise up to 0x7fffffffff. A outcome of 0x7f00000000 is not correct since it would contradict the earlier probed bounds where we know that the result should have been in [0x200,0x400] in u32 space. Therefore, tests with such info will lead to wrong verifier assumptions later on like falsely predicting conditional jumps to be always taken, etc. The issue here is that __reg_bound_offset32()'s implementation from commit 581738a6 ("bpf: Provide better register bounds after jmp32 instructions") makes an incorrect range assumption: static void __reg_bound_offset32(struct bpf_reg_state *reg) { u64 mask = 0xffffFFFF; struct tnum range = tnum_range(reg->umin_value & mask, reg->umax_value & mask); struct tnum lo32 = tnum_cast(reg->var_off, 4); struct tnum hi32 = tnum_lshift(tnum_rshift(reg->var_off, 32), 32); reg->var_off = tnum_or(hi32, tnum_intersect(lo32, range)); } In the above walk-through example, __reg_bound_offset32() as-is chose a range after masking with 0xffffffff of [0x0,0x0] since umin:0x2000000000 and umax:0x4000000000 and therefore the lo32 part was clamped to 0x0 as well. However, in the umin:0x2000000000 and umax:0x4000000000 range above we'd end up with an actual possible interval of [0x0,0xffffffff] for u32 space instead. In case of the original reproducer, the situation looked as follows at insn 5 for r0: [...] 5: R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x0; 0x1ffffffff)) R1_w=invP808464432 R10=fp0 0x30303030 0x13030302f 5: (de) if w1 s<= w0 goto pc+0 R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x30303020; 0x10000001f)) R1_w=invP808464432 R10=fp0 0x30303030 0x13030302f [...] After the fall-through, we similarly forced the var_off result into the wrong range [0x30303030,0x3030302f] suggesting later on that fixed bits must only be of 0x30303020 with 0x10000001f unknowns whereas such assumption can only be made when both bounds in hi32 range match. Originally, I was thinking to fix this by moving reg into a temp reg and use proper coerce_reg_to_size() helper on the temp reg where we can then based on that define the range tnum for later intersection: static void __reg_bound_offset32(struct bpf_reg_state *reg) { struct bpf_reg_state tmp = *reg; struct tnum lo32, hi32, range; coerce_reg_to_size(&tmp, 4); range = tnum_range(tmp.umin_value, tmp.umax_value); lo32 = tnum_cast(reg->var_off, 4); hi32 = tnum_lshift(tnum_rshift(reg->var_off, 32), 32); reg->var_off = tnum_or(hi32, tnum_intersect(lo32, range)); } In the case of the concrete example, this gives us a more conservative unknown section. Thus, after knowing r1 <= 0x4000000000 and r1 >= 0x2000000000 and w1 <= 0x400 and w1 >= 0x200: max: 0b100000000000000000000000000000000000000 / 0x4000000000 var: 0b111111111111111111111111111111111111111 / 0x7fffffffff min: 0b010000000000000000000000000000000000000 / 0x2000000000 However, above new __reg_bound_offset32() has no effect on refining the knowledge of the register contents. Meaning, if the bounds in hi32 range mismatch we'll get the identity function given the range reg spans [0x0,0xffffffff] and we cast var_off into lo32 only to later on binary or it again with the hi32. Likewise, if the bounds in hi32 range match, then we mask both bounds with 0xffffffff, use the resulting umin/umax for the range to later intersect the lo32 with it. However, _prior_ called __reg_bound_offset() did already such intersection on the full reg and we therefore would only repeat the same operation on the lo32 part twice. Given this has no effect and the original commit had false assumptions, this patch reverts the code entirely which is also more straight forward for stable trees: apparently 581738a6 got auto-selected by Sasha's ML system and misclassified as a fix, so it got sucked into v5.4 where it should never have landed. A revert is low-risk also from a user PoV since it requires a recent kernel and llc to opt-into -mcpu=v3 BPF CPU to generate jmp32 instructions. A proper bounds refinement would need a significantly more complex approach which is currently being worked, but no stable material [0]. Hence revert is best option for stable. After the revert, the original reported program gets rejected as follows: 1: (7f) r0 >>= r0 2: (14) w0 -= 808464432 3: (07) r0 += 808464432 4: (b7) r1 = 808464432 5: (de) if w1 s<= w0 goto pc+0 R0_w=invP(id=0,umin_value=808464432,umax_value=5103431727,var_off=(0x0; 0x1ffffffff)) R1_w=invP808464432 R10=fp0 6: (07) r0 += -2144337872 7: (14) w0 -= -1607454672 8: (25) if r0 > 0x30303030 goto pc+0 R0_w=invP(id=0,umax_value=808464432,var_off=(0x0; 0x3fffffff)) R1_w=invP808464432 R10=fp0 9: (76) if w0 s>= 0x303030 goto pc+2 R0=invP(id=0,umax_value=3158063,var_off=(0x0; 0x3fffff)) R1=invP808464432 R10=fp0 10: (30) r0 = *(u8 *)skb[808464432] BPF_LD_[ABS|IND] uses reserved fields processed 11 insns (limit 1000000) [...] [0] https://lore.kernel.org/bpf/158507130343.15666.8018068546764556975.stgit@john-Precision-5820-Tower/T/ Fixes: 581738a6 ("bpf: Provide better register bounds after jmp32 instructions") Reported-by:Anatoly Trosinenko <anatoly.trosinenko@gmail.com> Signed-off-by:
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- 29 Mar, 2020 12 commits
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Daniel Borkmann authored
KP Singh says: ==================== ** Motivation Google does analysis of rich runtime security data to detect and thwart threats in real-time. Currently, this is done in custom kernel modules but we would like to replace this with something that's upstream and useful to others. The current kernel infrastructure for providing telemetry (Audit, Perf etc.) is disjoint from access enforcement (i.e. LSMs). Augmenting the information provided by audit requires kernel changes to audit, its policy language and user-space components. Furthermore, building a MAC policy based on the newly added telemetry data requires changes to various LSMs and their respective policy languages. This patchset allows BPF programs to be attached to LSM hooks This facilitates a unified and dynamic (not requiring re-compilation of the kernel) audit and MAC policy. ** Why an LSM? Linux Security Modules target security behaviours rather than the kernel's API. For example, it's easy to miss out a newly added system call for executing processes (eg. execve, execveat etc.) but the LSM framework ensures that all process executions trigger the relevant hooks irrespective of how the process was executed. Allowing users to implement LSM hooks at runtime also benefits the LSM eco-system by enabling a quick feedback loop from the security community about the kind of behaviours that the LSM Framework should be targeting. ** How does it work? The patchset introduces a new eBPF (https://docs.cilium.io/en/v1.6/bpf/) program type BPF_PROG_TYPE_LSM which can only be attached to LSM hooks. Loading and attachment of BPF programs requires CAP_SYS_ADMIN. The new LSM registers nop functions (bpf_lsm_<hook_name>) as LSM hook callbacks. Their purpose is to provide a definite point where BPF programs can be attached as BPF_TRAMP_MODIFY_RETURN trampoline programs for hooks that return an int, and BPF_TRAMP_FEXIT trampoline programs for void LSM hooks. Audit logs can be written using a format chosen by the eBPF program to the perf events buffer or to global eBPF variables or maps and can be further processed in user-space. ** BTF Based Design The current design uses BTF: * https://facebookmicrosites.github.io/bpf/blog/2018/11/14/btf-enhancement.html * https://lwn.net/Articles/803258 which allows verifiable read-only structure accesses by field names rather than fixed offsets. This allows accessing the hook parameters using a dynamically created context which provides a certain degree of ABI stability: // Only declare the structure and fields intended to be used // in the program struct vm_area_struct { unsigned long vm_start; } __attribute__((preserve_access_index)); // Declare the eBPF program mprotect_audit which attaches to // to the file_mprotect LSM hook and accepts three arguments. SEC("lsm/file_mprotect") int BPF_PROG(mprotect_audit, struct vm_area_struct *vma, unsigned long reqprot, unsigned long prot, int ret) { unsigned long vm_start = vma->vm_start; return 0; } By relocating field offsets, BTF makes a large portion of kernel data structures readily accessible across kernel versions without requiring a large corpus of BPF helper functions and requiring recompilation with every kernel version. The BTF type information is also used by the BPF verifier to validate memory accesses within the BPF program and also prevents arbitrary writes to the kernel memory. The limitations of BTF compatibility are described in BPF Co-Re (http://vger.kernel.org/bpfconf2019_talks/bpf-core.pdf, i.e. field renames, #defines and changes to the signature of LSM hooks). This design imposes that the MAC policy (eBPF programs) be updated when the inspected kernel structures change outside of BTF compatibility guarantees. In practice, this is only required when a structure field used by a current policy is removed (or renamed) or when the used LSM hooks change. We expect the maintenance cost of these changes to be acceptable as compared to the design presented in the RFC. (https://lore.kernel.org/bpf/20190910115527.5235-1-kpsingh@chromium.org/). ** Usage Examples A simple example and some documentation is included in the patchset. In order to better illustrate the capabilities of the framework some more advanced prototype (not-ready for review) code has also been published separately: * Logging execution events (including environment variables and arguments) https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_audit_env.c * Detecting deletion of running executables: https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_detect_exec_unlink.c * Detection of writes to /proc/<pid>/mem: https://github.com/sinkap/linux-krsi/blob/patch/v1/examples/samples/bpf/lsm_audit_env.c We have updated Google's internal telemetry infrastructure and have started deploying this LSM on our Linux Workstations. This gives us more confidence in the real-world applications of such a system. ** Changelog: - v8 -> v9: https://lore.kernel.org/bpf/20200327192854.31150-1-kpsingh@chromium.org/ * Fixed a selftest crash when CONFIG_LSM doesn't have "bpf". * Added James' Ack. * Rebase. - v7 -> v8: https://lore.kernel.org/bpf/20200326142823.26277-1-kpsingh@chromium.org/ * Removed CAP_MAC_ADMIN check from bpf_lsm_verify_prog. LSMs can add it in their own bpf_prog hook. This can be revisited as a separate patch. * Added Andrii and James' Ack/Review tags. * Fixed an indentation issue and missing newlines in selftest error a cases. * Updated a comment as suggested by Alexei. * Updated the documentation to use the newer libbpf API and some other fixes. * Rebase - v6 -> v7: https://lore.kernel.org/bpf/20200325152629.6904-1-kpsingh@chromium.org/ * Removed __weak from the LSM attachment nops per Kees' suggestion. Will send a separate patch (if needed) to update the noinline definition in include/linux/compiler_attributes.h. * waitpid to wait specifically for the forked child in selftests. * Comment format fixes in security/... as suggested by Casey. * Added Acks from Kees and Andrii and Casey's Reviewed-by: tags to the respective patches. * Rebase - v5 -> v6: https://lore.kernel.org/bpf/20200323164415.12943-1-kpsingh@chromium.org/ * Updated LSM_HOOK macro to define a default value and cleaned up the BPF LSM hook declarations. * Added Yonghong's Acks and Kees' Reviewed-by tags. * Simplification of the selftest code. * Rebase and fixes suggested by Andrii and Yonghong and some other minor fixes noticed in internal review. - v4 -> v5: https://lore.kernel.org/bpf/20200220175250.10795-1-kpsingh@chromium.org/ * Removed static keys and special casing of BPF calls from the LSM framework. * Initialized the BPF callbacks (nops) as proper LSM hooks. * Updated to using the newly introduced BPF_TRAMP_MODIFY_RETURN trampolines in https://lkml.org/lkml/2020/3/4/877 * Addressed Andrii's feedback and rebased. - v3 -> v4: * Moved away from allocating a separate security_hook_heads and adding a new special case for arch_prepare_bpf_trampoline to using BPF fexit trampolines called from the right place in the LSM hook and toggled by static keys based on the discussion in: https://lore.kernel.org/bpf/CAG48ez25mW+_oCxgCtbiGMX07g_ph79UOJa07h=o_6B6+Q-u5g@mail.gmail.com/ * Since the code does not deal with security_hook_heads anymore, it goes from "being a BPF LSM" to "BPF program attachment to LSM hooks". * Added a new test case which ensures that the BPF programs' return value is reflected by the LSM hook. - v2 -> v3 does not change the overall design and has some minor fixes: * LSM_ORDER_LAST is introduced to represent the behaviour of the BPF LSM * Fixed the inadvertent clobbering of the LSM Hook error codes * Added GPL license requirement to the commit log * The lsm_hook_idx is now the more conventional 0-based index * Some changes were split into a separate patch ("Load btf_vmlinux only once per object") https://lore.kernel.org/bpf/20200117212825.11755-1-kpsingh@chromium.org/ * Addressed Andrii's feedback on the BTF implementation * Documentation update for using generated vmlinux.h to simplify programs * Rebase - Changes since v1: https://lore.kernel.org/bpf/20191220154208.15895-1-kpsingh@chromium.org * Eliminate the requirement to maintain LSM hooks separately in security/bpf/hooks.h Use BPF trampolines to dynamically allocate security hooks * Drop the use of securityfs as bpftool provides the required introspection capabilities. Update the tests to use the bpf_skeleton and global variables * Use O_CLOEXEC anonymous fds to represent BPF attachment in line with the other BPF programs with the possibility to use bpf program pinning in the future to provide "permanent attachment". * Drop the logic based on prog names for handling re-attachment. * Drop bpf_lsm_event_output from this series and send it as a separate patch. ==================== Signed-off-by:
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KP Singh authored
Document how eBPF programs (BPF_PROG_TYPE_LSM) can be loaded and attached (BPF_LSM_MAC) to the LSM hooks. Signed-off-by:
Brendan Jackman <jackmanb@google.com> Reviewed-by:
Florent Revest <revest@google.com> Reviewed-by:
Thomas Garnier <thgarnie@google.com> Reviewed-by:
James Morris <jamorris@linux.microsoft.com> Link: https://lore.kernel.org/bpf/20200329004356.27286-9-kpsingh@chromium.org
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KP Singh authored
* Load/attach a BPF program that hooks to file_mprotect (int) and bprm_committed_creds (void). * Perform an action that triggers the hook. * Verify if the audit event was received using the shared global variables for the process executed. * Verify if the mprotect returns a -EPERM. Signed-off-by:
Andrii Nakryiko <andriin@fb.com> Link: https://lore.kernel.org/bpf/20200329004356.27286-8-kpsingh@chromium.org
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KP Singh authored
Since BPF_PROG_TYPE_LSM uses the same attaching mechanism as BPF_PROG_TYPE_TRACING, the common logic is refactored into a static function bpf_program__attach_btf_id. A new API call bpf_program__attach_lsm is still added to avoid userspace conflicts if this ever changes in the future. Signed-off-by:
Yonghong Song <yhs@fb.com> Acked-by:
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KP Singh authored
* The hooks are initialized using the definitions in include/linux/lsm_hook_defs.h. * The LSM can be enabled / disabled with CONFIG_BPF_LSM. Signed-off-by:
Kees Cook <keescook@chromium.org> Acked-by:
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KP Singh authored
JITed BPF programs are dynamically attached to the LSM hooks using BPF trampolines. The trampoline prologue generates code to handle conversion of the signature of the hook to the appropriate BPF context. The allocated trampoline programs are attached to the nop functions initialized as LSM hooks. BPF_PROG_TYPE_LSM programs must have a GPL compatible license and and need CAP_SYS_ADMIN (required for loading eBPF programs). Upon attachment: * A BPF fexit trampoline is used for LSM hooks with a void return type. * A BPF fmod_ret trampoline is used for LSM hooks which return an int. The attached programs can override the return value of the bpf LSM hook to indicate a MAC Policy decision. Signed-off-by:
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KP Singh authored
When CONFIG_BPF_LSM is enabled, nop functions, bpf_lsm_<hook_name>, are generated for each LSM hook. These functions are initialized as LSM hooks in a subsequent patch. Signed-off-by:
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KP Singh authored
The information about the different types of LSM hooks is scattered in two locations i.e. union security_list_options and struct security_hook_heads. Rather than duplicating this information even further for BPF_PROG_TYPE_LSM, define all the hooks with the LSM_HOOK macro in lsm_hook_defs.h which is then used to generate all the data structures required by the LSM framework. The LSM hooks are defined as: LSM_HOOK(<return_type>, <default_value>, <hook_name>, args...) with <default_value> acccessible in security.c as: LSM_RET_DEFAULT(<hook_name>) Signed-off-by:
Casey Schaufler <casey@schaufler-ca.com> Acked-by:
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KP Singh authored
Introduce types and configs for bpf programs that can be attached to LSM hooks. The programs can be enabled by the config option CONFIG_BPF_LSM. Signed-off-by:
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Toke Høiland-Jørgensen authored
This adds a test to exercise the new bpf_map__set_initial_value() function. The test simply overrides the global data section with all zeroes, and checks that the new value makes it into the kernel map on load. Signed-off-by:
Toke Høiland-Jørgensen <toke@redhat.com> Signed-off-by:
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Toke Høiland-Jørgensen authored
For internal maps (most notably the maps backing global variables), libbpf uses an internal mmaped area to store the data after opening the object. This data is subsequently copied into the kernel map when the object is loaded. This adds a function to set a new value for that data, which can be used to before it is loaded into the kernel. This is especially relevant for RODATA maps, since those are frozen on load. Signed-off-by:
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Daniel Borkmann authored
Fix a redefinition of 'net_gen_cookie' error that was overlooked when net ns is not configured. Fixes: f318903c ("bpf: Add netns cookie and enable it for bpf cgroup hooks") Reported-by:
kbuild test robot <lkp@intel.com> Signed-off-by:
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- 28 Mar, 2020 15 commits
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Alexei Starovoitov authored
Toke Høiland-Jørgensen says: ==================== This series adds support for atomically replacing the XDP program loaded on an interface. This is achieved by means of a new netlink attribute that can specify the expected previous program to replace on the interface. If set, the kernel will compare this "expected fd" attribute with the program currently loaded on the interface, and reject the operation if it does not match. With this primitive, userspace applications can avoid stepping on each other's toes when simultaneously updating the loaded XDP program. Changelog: v4: - Switch back to passing FD instead of ID (Andrii) - Rename flag to XDP_FLAGS_REPLACE (for consistency with other similar uses) v3: - Pass existing ID instead of FD (Jakub) - Use opts struct for new libbpf function (Andrii) v2: - Fix checkpatch nits and add .strict_start_type to netlink policy (Jakub) ==================== Signed-off-by: -
Toke Høiland-Jørgensen authored
This adds tests for the various replacement operations using IFLA_XDP_EXPECTED_FD. Signed-off-by:
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Toke Høiland-Jørgensen authored
This adds a new function to set the XDP fd while specifying the FD of the program to replace, using the newly added IFLA_XDP_EXPECTED_FD netlink parameter. The new function uses the opts struct mechanism to be extendable in the future. Signed-off-by:
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Toke Høiland-Jørgensen authored
This adds the IFLA_XDP_EXPECTED_FD netlink attribute definition and the XDP_FLAGS_REPLACE flag to if_link.h in tools/include. Signed-off-by:
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Toke Høiland-Jørgensen authored
While it is currently possible for userspace to specify that an existing XDP program should not be replaced when attaching to an interface, there is no mechanism to safely replace a specific XDP program with another. This patch adds a new netlink attribute, IFLA_XDP_EXPECTED_FD, which can be set along with IFLA_XDP_FD. If set, the kernel will check that the program currently loaded on the interface matches the expected one, and fail the operation if it does not. This corresponds to a 'cmpxchg' memory operation. Setting the new attribute with a negative value means that no program is expected to be attached, which corresponds to setting the UPDATE_IF_NOEXIST flag. A new companion flag, XDP_FLAGS_REPLACE, is also added to explicitly request checking of the EXPECTED_FD attribute. This is needed for userspace to discover whether the kernel supports the new attribute. Signed-off-by:
Jakub Kicinski <kuba@kernel.org> Link: https://lore.kernel.org/bpf/158515700640.92963.3551295145441017022.stgit@toke.dk
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Jean-Philippe Menil authored
Fix build warnings when building net/bpf/test_run.o with W=1 due to missing prototype for bpf_fentry_test{1..6}. Instead of declaring prototypes, turn off warnings with __diag_{push,ignore,pop} as pointed out by Alexei. Signed-off-by:Jean-Philippe Menil <jpmenil@gmail.com> Signed-off-by:
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Fletcher Dunn authored
Fix a sharp edge in xsk_umem__create and xsk_socket__create. Almost all of the members of the ring buffer structs are initialized, but the "cached_xxx" variables are not all initialized. The caller is required to zero them. This is needlessly dangerous. The results if you don't do it can be very bad. For example, they can cause xsk_prod_nb_free and xsk_cons_nb_avail to return values greater than the size of the queue. xsk_ring_cons__peek can return an index that does not refer to an item that has been queued. I have confirmed that without this change, my program misbehaves unless I memset the ring buffers to zero before calling the function. Afterwards, my program works without (or with) the memset. Signed-off-by:
Fletcher Dunn <fletcherd@valvesoftware.com> Signed-off-by:
Magnus Karlsson <magnus.karlsson@intel.com> Link: https://lore.kernel.org/bpf/85f12913cde94b19bfcb598344701c38@valvesoftware.com
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Alexei Starovoitov authored
Daniel Borkmann says: ==================== This adds various straight-forward helper improvements and additions to BPF cgroup based connect(), sendmsg(), recvmsg() and bind-related hooks which would allow to implement more fine-grained policies and improve current load balancer limitations we're seeing. For details please see individual patches. I've tested them on Kubernetes & Cilium and also added selftests for the small verifier extension. Thanks! ==================== Signed-off-by: -
Daniel Borkmann authored
Add various tests to make sure the verifier keeps catching them: # ./test_verifier [...] #230/p pass ctx or null check, 1: ctx OK #231/p pass ctx or null check, 2: null OK #232/p pass ctx or null check, 3: 1 OK #233/p pass ctx or null check, 4: ctx - const OK #234/p pass ctx or null check, 5: null (connect) OK #235/p pass ctx or null check, 6: null (bind) OK #236/p pass ctx or null check, 7: ctx (bind) OK #237/p pass ctx or null check, 8: null (bind) OK [...] Summary: 1595 PASSED, 0 SKIPPED, 0 FAILED Signed-off-by:
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Daniel Borkmann authored
We already have the bpf_get_current_uid_gid() helper enabled, and given we now have perf event RB output available for connect(), sendmsg(), recvmsg() and bind-related hooks, add a trivial change to enable bpf_get_current_pid_tgid() and bpf_get_current_comm() as well. Signed-off-by:
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Daniel Borkmann authored
Enable the bpf_get_current_cgroup_id() helper for connect(), sendmsg(), recvmsg() and bind-related hooks in order to retrieve the cgroup v2 context which can then be used as part of the key for BPF map lookups, for example. Given these hooks operate in process context 'current' is always valid and pointing to the app that is performing mentioned syscalls if it's subject to a v2 cgroup. Also with same motivation of commit 77236281 ("bpf: Introduce bpf_skb_ancestor_cgroup_id helper") enable retrieval of ancestor from current so the cgroup id can be used for policy lookups which can then forbid connect() / bind(), for example. Signed-off-by:
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Daniel Borkmann authored
Today, Kubernetes is still operating on cgroups v1, however, it is possible to retrieve the task's classid based on 'current' out of connect(), sendmsg(), recvmsg() and bind-related hooks for orchestrators which attach to the root cgroup v2 hook in a mixed env like in case of Cilium, for example, in order to then correlate certain pod traffic and use it as part of the key for BPF map lookups. Signed-off-by:
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Daniel Borkmann authored
In Cilium we're mainly using BPF cgroup hooks today in order to implement kube-proxy free Kubernetes service translation for ClusterIP, NodePort (*), ExternalIP, and LoadBalancer as well as HostPort mapping [0] for all traffic between Cilium managed nodes. While this works in its current shape and avoids packet-level NAT for inter Cilium managed node traffic, there is one major limitation we're facing today, that is, lack of netns awareness. In Kubernetes, the concept of Pods (which hold one or multiple containers) has been built around network namespaces, so while we can use the global scope of attaching to root BPF cgroup hooks also to our advantage (e.g. for exposing NodePort ports on loopback addresses), we also have the need to differentiate between initial network namespaces and non-initial one. For example, ExternalIP services mandate that non-local service IPs are not to be translated from the host (initial) network namespace as one example. Right now, we have an ugly work-around in place where non-local service IPs for ExternalIP services are not xlated from connect() and friends BPF hooks but instead via less efficient packet-level NAT on the veth tc ingress hook for Pod traffic. On top of determining whether we're in initial or non-initial network namespace we also have a need for a socket-cookie like mechanism for network namespaces scope. Socket cookies have the nice property that they can be combined as part of the key structure e.g. for BPF LRU maps without having to worry that the cookie could be recycled. We are planning to use this for our sessionAffinity implementation for services. Therefore, add a new bpf_get_netns_cookie() helper which would resolve both use cases at once: bpf_get_netns_cookie(NULL) would provide the cookie for the initial network namespace while passing the context instead of NULL would provide the cookie from the application's network namespace. We're using a hole, so no size increase; the assignment happens only once. Therefore this allows for a comparison on initial namespace as well as regular cookie usage as we have today with socket cookies. We could later on enable this helper for other program types as well as we would see need. (*) Both externalTrafficPolicy={Local|Cluster} types [0] https://github.com/cilium/cilium/blob/master/bpf/bpf_sock.cSigned-off-by: -
Daniel Borkmann authored
Currently, connect(), sendmsg(), recvmsg() and bind-related hooks are all lacking perf event rb output in order to push notifications or monitoring events up to user space. Back in commit a5a3a828 ("bpf: add perf event notificaton support for sock_ops"), I've worked with Sowmini to enable them for sock_ops where the context part is not used (as opposed to skbs for example where the packet data can be appended). Make the bpf_sockopt_event_output() helper generic and enable it for mentioned hooks. Signed-off-by:
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Daniel Borkmann authored
We currently make heavy use of the socket cookie in BPF's connect(), sendmsg() and recvmsg() hooks for load-balancing decisions. However, it is currently not enabled/implemented in BPF {post-}bind hooks where it can later be used in combination for correlation in the tc egress path, for example. Signed-off-by:
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