Currently, the verifier does not handle '<const> <cond_op> <non_const>' well.
For example,
...
10: (79) r1 = *(u64 *)(r10 -16) ; R1_w=scalar() R10=fp0
11: (b7) r2 = 0 ; R2_w=0
12: (2d) if r2 > r1 goto pc+2
13: (b7) r0 = 0
14: (95) exit
15: (65) if r1 s> 0x1 goto pc+3
16: (0f) r0 += r1
...
At insn 12, verifier decides both true and false branch are possible, but
actually only false branch is possible.
Currently, the verifier already supports patterns '<non_const> <cond_op> <const>.
Add support for patterns '<const> <cond_op> <non_const>' in a similar way.
Also fix selftest 'verifier_bounds_mix_sign_unsign/bounds checks mixing signed and unsigned, variant 10'
due to this change.
Signed-off-by: Yonghong Song <yhs@xxxxxx>
---
kernel/bpf/verifier.c | 12 ++++++++++++
.../bpf/progs/verifier_bounds_mix_sign_unsign.c | 2 +-
2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 90bb6d25bc9c..d070943a8ba1 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -13302,6 +13302,18 @@ static int check_cond_jmp_op(struct bpf_verifier_env *env,
src_reg->var_off.value,
opcode,
is_jmp32);
+ } else if (dst_reg->type == SCALAR_VALUE &&
+ is_jmp32 && tnum_is_const(tnum_subreg(dst_reg->var_off))) {
+ pred = is_branch_taken(src_reg,
+ tnum_subreg(dst_reg->var_off).value,
+ flip_opcode(opcode),
+ is_jmp32);
+ } else if (dst_reg->type == SCALAR_VALUE &&
+ !is_jmp32 && tnum_is_const(dst_reg->var_off)) {
+ pred = is_branch_taken(src_reg,
+ dst_reg->var_off.value,
+ flip_opcode(opcode),
+ is_jmp32);
} else if (reg_is_pkt_pointer_any(dst_reg) &&
reg_is_pkt_pointer_any(src_reg) &&
!is_jmp32) {
diff --git a/tools/testing/selftests/bpf/progs/verifier_bounds_mix_sign_unsign.c b/tools/testing/selftests/bpf/progs/verifier_bounds_mix_sign_unsign.c
index 91a66357896a..4f40144748a5 100644
--- a/tools/testing/selftests/bpf/progs/verifier_bounds_mix_sign_unsign.c
+++ b/tools/testing/selftests/bpf/progs/verifier_bounds_mix_sign_unsign.c
@@ -354,7 +354,7 @@ __naked void signed_and_unsigned_variant_10(void)
call %[bpf_map_lookup_elem]; \
if r0 == 0 goto l0_%=; \
r1 = *(u64*)(r10 - 16); \
- r2 = 0; \
+ r2 = -1; \
if r2 > r1 goto l1_%=; \
r0 = 0; \
exit; \
--
2.34.1
