From: Andrii Nakryiko Date: Sun, 22 Oct 2023 20:57:37 +0000 (-0700) Subject: bpf: Improve JEQ/JNE branch taken logic X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=42d31dd601fa43b9afdf069d1ba410b2306a4c76;p=users%2Fjedix%2Flinux-maple.git bpf: Improve JEQ/JNE branch taken logic When determining if an if/else branch will always or never be taken, use signed range knowledge in addition to currently used unsigned range knowledge. If either signed or unsigned range suggests that condition is always/never taken, return corresponding branch_taken verdict. Current use of unsigned range for this seems arbitrary and unnecessarily incomplete. It is possible for *signed* operations to be performed on register, which could "invalidate" unsigned range for that register. In such case branch_taken will be artificially useless, even if we can still tell that some constant is outside of register value range based on its signed bounds. veristat-based validation shows zero differences across selftests, Cilium, and Meta-internal BPF object files. Signed-off-by: Andrii Nakryiko Signed-off-by: Daniel Borkmann Acked-by: Shung-Hsi Yu Link: https://lore.kernel.org/bpf/20231022205743.72352-2-andrii@kernel.org --- diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 98f9d0f35931..857d76694517 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -14031,12 +14031,16 @@ static int is_branch32_taken(struct bpf_reg_state *reg, u32 val, u8 opcode) return !!tnum_equals_const(subreg, val); else if (val < reg->u32_min_value || val > reg->u32_max_value) return 0; + else if (sval < reg->s32_min_value || sval > reg->s32_max_value) + return 0; break; case BPF_JNE: if (tnum_is_const(subreg)) return !tnum_equals_const(subreg, val); else if (val < reg->u32_min_value || val > reg->u32_max_value) return 1; + else if (sval < reg->s32_min_value || sval > reg->s32_max_value) + return 1; break; case BPF_JSET: if ((~subreg.mask & subreg.value) & val) @@ -14108,12 +14112,16 @@ static int is_branch64_taken(struct bpf_reg_state *reg, u64 val, u8 opcode) return !!tnum_equals_const(reg->var_off, val); else if (val < reg->umin_value || val > reg->umax_value) return 0; + else if (sval < reg->smin_value || sval > reg->smax_value) + return 0; break; case BPF_JNE: if (tnum_is_const(reg->var_off)) return !tnum_equals_const(reg->var_off, val); else if (val < reg->umin_value || val > reg->umax_value) return 1; + else if (sval < reg->smin_value || sval > reg->smax_value) + return 1; break; case BPF_JSET: if ((~reg->var_off.mask & reg->var_off.value) & val)