selftests/bpf: Tests for per-insn sync_linked_regs() precision tracking

Add a few test cases to verify precision tracking for scalars gaining
range because of sync_linked_regs():
- check what happens when more than 6 registers might gain range in
  sync_linked_regs();
- check if precision is propagated correctly when operand of
  conditional jump gained range in sync_linked_regs() and one of
  linked registers is marked precise;
- check if precision is propagated correctly when operand of
  conditional jump gained range in sync_linked_regs() and a
  other-linked operand of the conditional jump is marked precise;
- add a minimized reproducer for precision tracking bug reported in [0];
- Check that mark_chain_precision() for one of the conditional jump
  operands does not trigger equal scalars precision propagation.

[0] https://lore.kernel.org/bpf/CAEf4BzZ0xidVCqB47XnkXcNhkPWF6_nTV7yt+_Lf0kcFEut2Mg@mail.gmail.com/Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20240718202357.1746514-4-eddyz87@gmail.com

tools/testing/selftests/bpf/progs/verifier_scalar_ids.c

@@ -47,6 +47,72 @@ __naked void linked_regs_bpf_k(void)
 	: __clobber_all);
 }
 
+/* Registers r{0,1,2} share same ID when 'if r1 > ...' insn is processed,
+ * check that verifier marks r{1,2} as precise while backtracking
+ * 'if r1 > ...' with r0 already marked.
+ */
+SEC("socket")
+__success __log_level(2)
+__flag(BPF_F_TEST_STATE_FREQ)
+__msg("frame0: regs=r0 stack= before 5: (2d) if r1 > r3 goto pc+0")
+__msg("frame0: parent state regs=r0,r1,r2,r3 stack=:")
+__msg("frame0: regs=r0,r1,r2,r3 stack= before 4: (b7) r3 = 7")
+__naked void linked_regs_bpf_x_src(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id == r2.id */
+	"r1 = r0;"
+	"r2 = r0;"
+	"r3 = 7;"
+	"if r1 > r3 goto +0;"
+	/* force r0 to be precise, this eventually marks r1 and r2 as
+	 * precise as well because of shared IDs
+	 */
+	"r4 = r10;"
+	"r4 += r0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+/* Registers r{0,1,2} share same ID when 'if r1 > r3' insn is processed,
+ * check that verifier marks r{0,1,2} as precise while backtracking
+ * 'if r1 > r3' with r3 already marked.
+ */
+SEC("socket")
+__success __log_level(2)
+__flag(BPF_F_TEST_STATE_FREQ)
+__msg("frame0: regs=r3 stack= before 5: (2d) if r1 > r3 goto pc+0")
+__msg("frame0: parent state regs=r0,r1,r2,r3 stack=:")
+__msg("frame0: regs=r0,r1,r2,r3 stack= before 4: (b7) r3 = 7")
+__naked void linked_regs_bpf_x_dst(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id == r2.id */
+	"r1 = r0;"
+	"r2 = r0;"
+	"r3 = 7;"
+	"if r1 > r3 goto +0;"
+	/* force r0 to be precise, this eventually marks r1 and r2 as
+	 * precise as well because of shared IDs
+	 */
+	"r4 = r10;"
+	"r4 += r3;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
 /* Same as linked_regs_bpf_k, but break one of the
  * links, note that r1 is absent from regs=... in __msg below.
  */
@@ -280,6 +346,105 @@ __naked void precision_two_ids(void)
 	: __clobber_all);
 }
 
+SEC("socket")
+__success __log_level(2)
+__flag(BPF_F_TEST_STATE_FREQ)
+/* check thar r0 and r6 have different IDs after 'if',
+ * collect_linked_regs() can't tie more than 6 registers for a single insn.
+ */
+__msg("8: (25) if r0 > 0x7 goto pc+0         ; R0=scalar(id=1")
+__msg("9: (bf) r6 = r6                       ; R6_w=scalar(id=2")
+/* check that r{0-5} are marked precise after 'if' */
+__msg("frame0: regs=r0 stack= before 8: (25) if r0 > 0x7 goto pc+0")
+__msg("frame0: parent state regs=r0,r1,r2,r3,r4,r5 stack=:")
+__naked void linked_regs_too_many_regs(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r{0-6} IDs */
+	"r1 = r0;"
+	"r2 = r0;"
+	"r3 = r0;"
+	"r4 = r0;"
+	"r5 = r0;"
+	"r6 = r0;"
+	/* propagate range for r{0-6} */
+	"if r0 > 7 goto +0;"
+	/* make r6 appear in the log */
+	"r6 = r6;"
+	/* force r0 to be precise,
+	 * this would cause r{0-4} to be precise because of shared IDs
+	 */
+	"r7 = r10;"
+	"r7 += r0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
+SEC("socket")
+__failure __log_level(2)
+__flag(BPF_F_TEST_STATE_FREQ)
+__msg("regs=r7 stack= before 5: (3d) if r8 >= r0")
+__msg("parent state regs=r0,r7,r8")
+__msg("regs=r0,r7,r8 stack= before 4: (25) if r0 > 0x1")
+__msg("div by zero")
+__naked void linked_regs_broken_link_2(void)
+{
+	asm volatile (
+	"call %[bpf_get_prandom_u32];"
+	"r7 = r0;"
+	"r8 = r0;"
+	"call %[bpf_get_prandom_u32];"
+	"if r0 > 1 goto +0;"
+	/* r7.id == r8.id,
+	 * thus r7 precision implies r8 precision,
+	 * which implies r0 precision because of the conditional below.
+	 */
+	"if r8 >= r0 goto 1f;"
+	/* break id relation between r7 and r8 */
+	"r8 += r8;"
+	/* make r7 precise */
+	"if r7 == 0 goto 1f;"
+	"r0 /= 0;"
+"1:"
+	"r0 = 42;"
+	"exit;"
+	:
+	: __imm(bpf_get_prandom_u32)
+	: __clobber_all);
+}
+
+/* Check that mark_chain_precision() for one of the conditional jump
+ * operands does not trigger equal scalars precision propagation.
+ */
+SEC("socket")
+__success __log_level(2)
+__msg("3: (25) if r1 > 0x100 goto pc+0")
+__msg("frame0: regs=r1 stack= before 2: (bf) r1 = r0")
+__naked void cjmp_no_linked_regs_trigger(void)
+{
+	asm volatile (
+	/* r0 = random number up to 0xff */
+	"call %[bpf_ktime_get_ns];"
+	"r0 &= 0xff;"
+	/* tie r0.id == r1.id */
+	"r1 = r0;"
+	/* the jump below would be predicted, thus r1 would be marked precise,
+	 * this should not imply precision mark for r0
+	 */
+	"if r1 > 256 goto +0;"
+	"r0 = 0;"
+	"exit;"
+	:
+	: __imm(bpf_ktime_get_ns)
+	: __clobber_all);
+}
+
 /* Verify that check_ids() is used by regsafe() for scalars.
  *
  * r9 = ... some pointer with range X ...