From 953d9f5beaf75e88c69a13d70ce424cd606a29f5 Mon Sep 17 00:00:00 2001 From: Yonghong Song Date: Thu, 6 Apr 2023 09:45:05 -0700 Subject: [PATCH] bpf: Improve handling of pattern ' ' in verifier Currently, the verifier does not handle ' ' 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 ' . Add support for patterns ' ' 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 Acked-by: Dave Marchevsky Acked-by: Andrii Nakryiko Link: https://lore.kernel.org/r/20230406164505.1046801-1-yhs@fb.com Signed-off-by: Alexei Starovoitov --- 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 5c6b90e384a5..3660b573048a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13356,6 +13356,18 @@ 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; \