diff options
| author | Puranjay Mohan <puranjay@kernel.org> | 2026-02-04 07:17:37 -0800 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-02-04 13:35:28 -0800 |
| commit | 7a433e519364c3c19643e5c857f4fbfaebec441c (patch) | |
| tree | ea9532fb93d067fbd9be66317ec5064d5a925cc3 /include/linux | |
| parent | b2821311abbd05d3340ad7f09fe89f088572b682 (diff) | |
bpf: Support negative offsets, BPF_SUB, and alu32 for linked register tracking
Previously, the verifier only tracked positive constant deltas between
linked registers using BPF_ADD. This limitation meant patterns like:
r1 = r0;
r1 += -4;
if r1 s>= 0 goto l0_%=; // r1 >= 0 implies r0 >= 4
// verifier couldn't propagate bounds back to r0
if r0 != 0 goto l0_%=;
r0 /= 0; // Verifier thinks this is reachable
l0_%=:
Similar limitation exists for 32-bit registers.
With this change, the verifier can now track negative deltas in reg->off
enabling bound propagation for the above pattern.
For alu32, we make sure the destination register has the upper 32 bits
as 0s before creating the link. BPF_ADD_CONST is split into
BPF_ADD_CONST64 and BPF_ADD_CONST32, the latter is used in case of alu32
and sync_linked_regs uses this to zext the result if known_reg has this
flag.
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260204151741.2678118-2-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/bpf_verifier.h | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 746025df82c8..ef8e45a362d9 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -147,8 +147,12 @@ struct bpf_reg_state { * registers. Example: * r1 = r2; both will have r1->id == r2->id == N * r1 += 10; r1->id == N | BPF_ADD_CONST and r1->off == 10 + * r3 = r2; both will have r3->id == r2->id == N + * w3 += 10; r3->id == N | BPF_ADD_CONST32 and r3->off == 10 */ -#define BPF_ADD_CONST (1U << 31) +#define BPF_ADD_CONST64 (1U << 31) +#define BPF_ADD_CONST32 (1U << 30) +#define BPF_ADD_CONST (BPF_ADD_CONST64 | BPF_ADD_CONST32) u32 id; /* PTR_TO_SOCKET and PTR_TO_TCP_SOCK could be a ptr returned * from a pointer-cast helper, bpf_sk_fullsock() and |