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  1. 08 Apr, 2021 8 commits
    • Michael Ellerman's avatar
      powerpc/mm/64s/hash: Add real-mode change_memory_range() for hash LPAR · 87e65ad7
      Michael Ellerman authored 
      When we enabled STRICT_KERNEL_RWX we received some reports of boot
failures when using the Hash MMU and running under phyp. The crashes
are intermittent, and often exhibit as a completely unresponsive
system, or possibly an oops.

One example, which was caught in xmon:

  [   14.068327][    T1] devtmpfs: mounted
  [   14.069302][    T1] Freeing unused kernel memory: 5568K
  [   14.142060][  T347] BUG: Unable to handle kernel instruction fetch
  [   14.142063][    T1] Run /sbin/init as init process
  [   14.142074][  T347] Faulting instruction address: 0xc000000000004400
  cpu 0x2: Vector: 400 (Instruction Access) at [c00000000c7475e0]
      pc: c000000000004400: exc_virt_0x4400_instruction_access+0x0/0x80
      lr: c0000000001862d4: update_rq_clock+0x44/0x110
      sp: c00000000c747880
     msr: 8000000040001031
    current = 0xc00000000c60d380
    paca    = 0xc00000001ec9de80   irqmask: 0x03   irq_happened: 0x01
      pid   = 347, comm = kworker/2:1
  ...
  enter ? for help
  [c00000000c747880] c0000000001862d4 update_rq_clock+0x44/0x110 (unreliable)
  [c00000000c7478f0] c000000000198794 update_blocked_averages+0xb4/0x6d0
  [c00000000c7479f0] c000000000198e40 update_nohz_stats+0x90/0xd0
  [c00000000c747a20] c0000000001a13b4 _nohz_idle_balance+0x164/0x390
  [c00000000c747b10] c0000000001a1af8 newidle_balance+0x478/0x610
  [c00000000c747be0] c0000000001a1d48 pick_next_task_fair+0x58/0x480
  [c00000000c747c40] c000000000eaab5c __schedule+0x12c/0x950
  [c00000000c747cd0] c000000000eab3e8 schedule+0x68/0x120
  [c00000000c747d00] c00000000016b730 worker_thread+0x130/0x640
  [c00000000c747da0] c000000000174d50 kthread+0x1a0/0x1b0
  [c00000000c747e10] c00000000000e0f0 ret_from_kernel_thread+0x5c/0x6c

This shows that CPU 2, which was idle, woke up and then appears to
randomly take an instruction fault on a completely valid area of
kernel text.

The cause turns out to be the call to hash__mark_rodata_ro(), late in
boot. Due to the way we layout text and rodata, that function actually
changes the permissions for all of text and rodata to read-only plus
execute.

To do the permission change we use a hypervisor call, H_PROTECT. On
phyp that appears to be implemented by briefly removing the mapping of
the kernel text, before putting it back with the updated permissions.
If any other CPU is executing during that window, it will see spurious
faults on the kernel text and/or data, leading to crashes.

To fix it we use stop machine to collect all other CPUs, and then have
them drop into real mode (MMU off), while we change the mapping. That
way they are unaffected by the mapping temporarily disappearing.

We don't see this bug on KVM because KVM always use VPM=1, where
faults are directed to the hypervisor, and the fault will be
serialised vs the h_protect() by HPTE_V_HVLOCK.
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210331003845.216246-5-mpe@ellerman.id.au
      87e65ad7
    • Michael Ellerman's avatar
      powerpc/mm/64s/hash: Factor out change_memory_range() · 6f223ebe
      Michael Ellerman authored 
      Pull the loop calling hpte_updateboltedpp() out of
hash__change_memory_range() into a helper function. We need it to be a
separate function for the next patch.
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210331003845.216246-4-mpe@ellerman.id.au
      6f223ebe
    • Michael Ellerman's avatar
      powerpc/64s: Use htab_convert_pte_flags() in hash__mark_rodata_ro() · 2c02e656
      Michael Ellerman authored 
      In hash__mark_rodata_ro() we pass the raw PP_RXXX value to
hash__change_memory_range(). That has the effect of setting the key to
zero, because PP_RXXX contains no key value.

Fix it by using htab_convert_pte_flags(), which knows how to convert a
pgprot into a pp value, including the key.

Fixes: d94b827e ("powerpc/book3s64/kuap: Use Key 3 for kernel mapping with hash translation")
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Reviewed-by: default avatarDaniel Axtens <dja@axtens.net>
Link: https://lore.kernel.org/r/20210331003845.216246-3-mpe@ellerman.id.au
      2c02e656
    • Michael Ellerman's avatar
      powerpc/pseries: Add key to flags in pSeries_lpar_hpte_updateboltedpp() · b56d55a5
      Michael Ellerman authored 
      The flags argument to plpar_pte_protect() (aka. H_PROTECT), includes
the key in bits 9-13, but currently we always set those bits to zero.

In the past that hasn't been a problem because we always used key 0
for the kernel, and updateboltedpp() is only used for kernel mappings.

However since commit d94b827e ("powerpc/book3s64/kuap: Use Key 3
for kernel mapping with hash translation") we are now inadvertently
changing the key (to zero) when we call plpar_pte_protect().

That hasn't broken anything because updateboltedpp() is only used for
STRICT_KERNEL_RWX, which is currently disabled on 64s due to other
bugs.

But we want to fix that, so first we need to pass the key correctly to
plpar_pte_protect(). We can't pass our newpp value directly in, we
have to convert it into the form expected by the hcall.

The hcall we're using here is H_PROTECT, which is specified in section
14.5.4.1.6 of LoPAPR v1.1.

It takes a `flags` parameter, and the description for flags says:

 * flags: AVPN, pp0, pp1, pp2, key0-key4, n, and for the CMO
   option: CMO Option flags as defined in Table 189‚

If you then go to the start of the parent section, 14.5.4.1, on page
405, it says:

Register Linkage (For hcall() tokens 0x04 - 0x18)
 * On Call
   * R3 function call token
   * R4 flags (see Table 178‚ “Page Frame Table Access flags field
     definition‚” on page 401)

Then you have to go to section 14.5.3, and on page 394 there is a list
of hcalls and their tokens (table 176), and there you can see that
H_PROTECT == 0x18.

Finally you can look at table 178, on page 401, where it specifies the
layout of the bits for the key:

 Bit     Function
 -----------------
 50-54 | key0-key4

Those are big-endian bit numbers, converting to normal bit numbers you
get bits 9-13, or 0x3e00.

In the kernel we have:

  #define HPTE_R_KEY_HI		ASM_CONST(0x3000000000000000)
  #define HPTE_R_KEY_LO		ASM_CONST(0x0000000000000e00)

So the LO bits of newpp are already in the right place, and the HI
bits need to be shifted down by 48.

Fixes: d94b827e ("powerpc/book3s64/kuap: Use Key 3 for kernel mapping with hash translation")
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210331003845.216246-2-mpe@ellerman.id.au
      b56d55a5
    • Michael Ellerman's avatar
      powerpc/mm/64s: Add _PAGE_KERNEL_ROX · 56bec2f9
      Michael Ellerman authored 
      In the past we had a fallback definition for _PAGE_KERNEL_ROX, but we
removed that in commit d82fd29c ("powerpc/mm: Distribute platform
specific PAGE and PMD flags and definitions") and added definitions
for each MMU family.

However we missed adding a definition for 64s, which was not really a
bug because it's currently not used.

But we'd like to use PAGE_KERNEL_ROX in a future patch so add a
definition now.
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210331003845.216246-1-mpe@ellerman.id.au
      56bec2f9
    • Jordan Niethe's avatar
      selftests/powerpc: Test for spurious kernel memory faults on radix · 29e3ea8c
      Jordan Niethe authored 
      Previously when mapping kernel memory on radix, no ptesync was
included which would periodically lead to unhandled spurious faults.
Mapping kernel memory is used when code patching with Strict RWX
enabled. As suggested by Chris Riedl, turning ftrace on and off does a
large amount of code patching so is a convenient way to see this kind
of fault.

Add a selftest to try and trigger this kind of a spurious fault. It
tests for 30 seconds which is usually long enough for the issue to
show up.
Signed-off-by: default avatarJordan Niethe <jniethe5@gmail.com>
[mpe: Rename it to better reflect what it does, rather than the symptom]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210208032957.1232102-2-jniethe5@gmail.com
      29e3ea8c
    • Jordan Niethe's avatar
      powerpc/64s: Fix pte update for kernel memory on radix · b8b2f37c
      Jordan Niethe authored 
      When adding a PTE a ptesync is needed to order the update of the PTE
with subsequent accesses otherwise a spurious fault may be raised.

radix__set_pte_at() does not do this for performance gains. For
non-kernel memory this is not an issue as any faults of this kind are
corrected by the page fault handler. For kernel memory these faults
are not handled. The current solution is that there is a ptesync in
flush_cache_vmap() which should be called when mapping from the
vmalloc region.

However, map_kernel_page() does not call flush_cache_vmap(). This is
troublesome in particular for code patching with Strict RWX on radix.
In do_patch_instruction() the page frame that contains the instruction
to be patched is mapped and then immediately patched. With no ordering
or synchronization between setting up the PTE and writing to the page
it is possible for faults.

As the code patching is done using __put_user_asm_goto() the resulting
fault is obscured - but using a normal store instead it can be seen:

  BUG: Unable to handle kernel data access on write at 0xc008000008f24a3c
  Faulting instruction address: 0xc00000000008bd74
  Oops: Kernel access of bad area, sig: 11 [#1]
  LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA PowerNV
  Modules linked in: nop_module(PO+) [last unloaded: nop_module]
  CPU: 4 PID: 757 Comm: sh Tainted: P           O      5.10.0-rc5-01361-ge3c1b78c8440-dirty #43
  NIP:  c00000000008bd74 LR: c00000000008bd50 CTR: c000000000025810
  REGS: c000000016f634a0 TRAP: 0300   Tainted: P           O       (5.10.0-rc5-01361-ge3c1b78c8440-dirty)
  MSR:  9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR: 44002884  XER: 00000000
  CFAR: c00000000007c68c DAR: c008000008f24a3c DSISR: 42000000 IRQMASK: 1

This results in the kind of issue reported here:
  https://lore.kernel.org/linuxppc-dev/15AC5B0E-A221-4B8C-9039-FA96B8EF7C88@lca.pw/

Chris Riedl suggested a reliable way to reproduce the issue:
  $ mount -t debugfs none /sys/kernel/debug
  $ (while true; do echo function > /sys/kernel/debug/tracing/current_tracer ; echo nop > /sys/kernel/debug/tracing/current_tracer ; done) &

Turning ftrace on and off does a large amount of code patching which
in usually less then 5min will crash giving a trace like:

   ftrace-powerpc: (____ptrval____): replaced (4b473b11) != old (60000000)
   ------------[ ftrace bug ]------------
   ftrace failed to modify
   [<c000000000bf8e5c>] napi_busy_loop+0xc/0x390
    actual:   11:3b:47:4b
   Setting ftrace call site to call ftrace function
   ftrace record flags: 80000001
    (1)
    expected tramp: c00000000006c96c
   ------------[ cut here ]------------
   WARNING: CPU: 4 PID: 809 at kernel/trace/ftrace.c:2065 ftrace_bug+0x28c/0x2e8
   Modules linked in: nop_module(PO-) [last unloaded: nop_module]
   CPU: 4 PID: 809 Comm: sh Tainted: P           O      5.10.0-rc5-01360-gf878ccaf250a #1
   NIP:  c00000000024f334 LR: c00000000024f330 CTR: c0000000001a5af0
   REGS: c000000004c8b760 TRAP: 0700   Tainted: P           O       (5.10.0-rc5-01360-gf878ccaf250a)
   MSR:  900000000282b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE>  CR: 28008848  XER: 20040000
   CFAR: c0000000001a9c98 IRQMASK: 0
   GPR00: c00000000024f330 c000000004c8b9f0 c000000002770600 0000000000000022
   GPR04: 00000000ffff7fff c000000004c8b6d0 0000000000000027 c0000007fe9bcdd8
   GPR08: 0000000000000023 ffffffffffffffd8 0000000000000027 c000000002613118
   GPR12: 0000000000008000 c0000007fffdca00 0000000000000000 0000000000000000
   GPR16: 0000000023ec37c5 0000000000000000 0000000000000000 0000000000000008
   GPR20: c000000004c8bc90 c0000000027a2d20 c000000004c8bcd0 c000000002612fe8
   GPR24: 0000000000000038 0000000000000030 0000000000000028 0000000000000020
   GPR28: c000000000ff1b68 c000000000bf8e5c c00000000312f700 c000000000fbb9b0
   NIP ftrace_bug+0x28c/0x2e8
   LR  ftrace_bug+0x288/0x2e8
   Call Trace:
     ftrace_bug+0x288/0x2e8 (unreliable)
     ftrace_modify_all_code+0x168/0x210
     arch_ftrace_update_code+0x18/0x30
     ftrace_run_update_code+0x44/0xc0
     ftrace_startup+0xf8/0x1c0
     register_ftrace_function+0x4c/0xc0
     function_trace_init+0x80/0xb0
     tracing_set_tracer+0x2a4/0x4f0
     tracing_set_trace_write+0xd4/0x130
     vfs_write+0xf0/0x330
     ksys_write+0x84/0x140
     system_call_exception+0x14c/0x230
     system_call_common+0xf0/0x27c

To fix this when updating kernel memory PTEs using ptesync.

Fixes: f1cb8f9b ("powerpc/64s/radix: avoid ptesync after set_pte and ptep_set_access_flags")
Signed-off-by: default avatarJordan Niethe <jniethe5@gmail.com>
Reviewed-by: default avatarNicholas Piggin <npiggin@gmail.com>
[mpe: Tidy up change log slightly]
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210208032957.1232102-1-jniethe5@gmail.com
      b8b2f37c
    • Bhaskar Chowdhury's avatar
      powerpc: Spelling/typo fixes · 4763d378
      Bhaskar Chowdhury authored 
      Various spelling/typo fixes.
Signed-off-by: default avatarBhaskar Chowdhury <unixbhaskar@gmail.com>
Acked-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
      4763d378
  3. 03 Apr, 2021 32 commits
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