On 4/30/2024 6:18 AM, Eduard Zingerman wrote:
On Mon, 2024-04-29 at 13:58 -0700, Andrii Nakryiko wrote:
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diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 8f0f2e21699e..b69c89bc5cfc 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -13478,6 +13478,28 @@ static void scalar32_min_max_and(struct bpf_reg_state *dst_reg, return; }
/* Special case: dst_reg is in range [-1, 0] */if (dst_reg->s32_min_value == -1 && dst_reg->s32_max_value == 0) {var32_off = tnum_union(src_reg->var_off, tnum_const(0));dst_reg->var_off = tnum_with_subreg(dst_reg->var_off, var32_off);dst_reg->u32_min_value = var32_off.value;dst_reg->u32_max_value = min(dst_reg->u32_max_value, umax_val);can you explain the logic behing u32 min/max updates, especially that we use completely different values for min/max and it's not clear why u32_min <= u32_max invariant will always hold. Same below
I agree with Andrii here. It appears that dst_reg.{min,max} fields should be set as {min(src.min, 0), max(src.max, 0)} for both signed and unsigned cases. Wdyt?
Agree, since 0 is the minimum unsigned number, the result range is equal to [0, src.u32_max].
dst_reg->s32_min_value = min_t(s32, src_reg->s32_min_value, 0);dst_reg->s32_max_value = max_t(s32, src_reg->s32_max_value, 0);return;}/* Special case: src_reg is in range [-1, 0] */if (src_reg->s32_min_value == -1 && src_reg->s32_max_value == 0) {var32_off = tnum_union(dst_reg->var_off, tnum_const(0));dst_reg->var_off = tnum_with_subreg(dst_reg->var_off, var32_off);dst_reg->u32_min_value = var32_off.value;dst_reg->u32_max_value = min(dst_reg->u32_max_value, umax_val);dst_reg->s32_min_value = min_t(s32, dst_reg->s32_min_value, 0);dst_reg->s32_max_value = max_t(s32, dst_reg->s32_max_value, 0);return;}/* We get our minimum from the var_off, since that's inherently * bitwise. Our maximum is the minimum of the operands' maxima. */[...]