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bpf, verifier: Improve precision of BPF_MUL #4708

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bpf, verifier: Improve precision of BPF_MUL #4708

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72 changes: 24 additions & 48 deletions kernel/bpf/verifier.c
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Original file line number Diff line number Diff line change
Expand Up @@ -13827,65 +13827,41 @@ static void scalar_min_max_sub(struct bpf_reg_state *dst_reg,
static void scalar32_min_max_mul(struct bpf_reg_state *dst_reg,
struct bpf_reg_state *src_reg)
{
s32 smin_val = src_reg->s32_min_value;
u32 umin_val = src_reg->u32_min_value;
u32 umax_val = src_reg->u32_max_value;
u32 *dst_umin = &dst_reg->u32_min_value;
u32 *dst_umax = &dst_reg->u32_max_value;

if (smin_val < 0 || dst_reg->s32_min_value < 0) {
/* Ain't nobody got time to multiply that sign */
__mark_reg32_unbounded(dst_reg);
return;
}
/* Both values are positive, so we can work with unsigned and
* copy the result to signed (unless it exceeds S32_MAX).
*/
if (umax_val > U16_MAX || dst_reg->u32_max_value > U16_MAX) {
/* Potential overflow, we know nothing */
__mark_reg32_unbounded(dst_reg);
return;
}
dst_reg->u32_min_value *= umin_val;
dst_reg->u32_max_value *= umax_val;
if (dst_reg->u32_max_value > S32_MAX) {
if (check_mul_overflow(*dst_umax, src_reg->u32_max_value, dst_umax) ||
check_mul_overflow(*dst_umin, src_reg->u32_min_value, dst_umin)) {
/* Overflow possible, we know nothing */
dst_reg->s32_min_value = S32_MIN;
dst_reg->s32_max_value = S32_MAX;
} else {
dst_reg->s32_min_value = dst_reg->u32_min_value;
dst_reg->s32_max_value = dst_reg->u32_max_value;
dst_reg->u32_min_value = 0;
dst_reg->u32_max_value = U32_MAX;
}

/* Set signed bounds to unbounded and improve precision in
* reg_bounds_sync()
*/
dst_reg->s32_min_value = S32_MIN;
dst_reg->s32_max_value = S32_MAX;
}

static void scalar_min_max_mul(struct bpf_reg_state *dst_reg,
struct bpf_reg_state *src_reg)
{
s64 smin_val = src_reg->smin_value;
u64 umin_val = src_reg->umin_value;
u64 umax_val = src_reg->umax_value;
u64 *dst_umin = &dst_reg->umin_value;
u64 *dst_umax = &dst_reg->umax_value;

if (smin_val < 0 || dst_reg->smin_value < 0) {
/* Ain't nobody got time to multiply that sign */
__mark_reg64_unbounded(dst_reg);
return;
}
/* Both values are positive, so we can work with unsigned and
* copy the result to signed (unless it exceeds S64_MAX).
*/
if (umax_val > U32_MAX || dst_reg->umax_value > U32_MAX) {
/* Potential overflow, we know nothing */
__mark_reg64_unbounded(dst_reg);
return;
}
dst_reg->umin_value *= umin_val;
dst_reg->umax_value *= umax_val;
if (dst_reg->umax_value > S64_MAX) {
if (check_mul_overflow(*dst_umax, src_reg->umax_value, dst_umax) ||
check_mul_overflow(*dst_umin, src_reg->umin_value, dst_umin)) {
/* Overflow possible, we know nothing */
dst_reg->smin_value = S64_MIN;
dst_reg->smax_value = S64_MAX;
} else {
dst_reg->smin_value = dst_reg->umin_value;
dst_reg->smax_value = dst_reg->umax_value;
dst_reg->umin_value = 0;
dst_reg->umax_value = U64_MAX;
}

/* Set signed bounds to unbounded and improve precision in
* reg_bounds_sync()
*/
dst_reg->smin_value = S64_MIN;
dst_reg->smax_value = S64_MAX;
}

static void scalar32_min_max_and(struct bpf_reg_state *dst_reg,
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