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| author | Daniel Borkmann <daniel@iogearbox.net> | 2026-04-15 15:14:03 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-04-15 22:08:03 +0300 |
| commit | 1dd8be4ec722ce54e4cace59f3a4ba658111b3ec (patch) | |
| tree | a6304987e6bef77d47982752ae571cbaa39b2672 | |
| parent | 48d83d94930eb4db4c93d2de44838b9455cff626 (diff) | |
| download | linux-1dd8be4ec722ce54e4cace59f3a4ba658111b3ec.tar.xz | |
bpf, arm64: Fix off-by-one in check_imm signed range check
check_imm(bits, imm) is used in the arm64 BPF JIT to verify that
a branch displacement (in arm64 instruction units) fits into the
signed N-bit immediate field of a B, B.cond or CBZ/CBNZ encoding
before it is handed to the encoder. The macro currently tests for
(imm > 0 && imm >> bits) || (imm < 0 && ~imm >> bits) which admits
values in [-2^N, 2^N) — effectively a signed (N+1)-bit range. A
signed N-bit field only holds [-2^(N-1), 2^(N-1)), so the check
admits one extra bit of range on each side.
In particular, for check_imm19(), values in [2^18, 2^19) slip past
the check but do not fit into the 19-bit signed imm19 field of
B.cond. aarch64_insn_encode_immediate() then masks the raw value
into the 19-bit field, setting bit 18 (the sign bit) and flipping
a forward branch into a backward one. Same class of issue exists
for check_imm26() and the B/BL encoding. Shift by (bits - 1)
instead of bits so the actual signed N-bit range is enforced.
Fixes: e54bcde3d69d ("arm64: eBPF JIT compiler")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20260415121403.639619-2-daniel@iogearbox.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
| -rw-r--r-- | arch/arm64/net/bpf_jit_comp.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c index adf84962d579..4aad9483f8a5 100644 --- a/arch/arm64/net/bpf_jit_comp.c +++ b/arch/arm64/net/bpf_jit_comp.c @@ -35,8 +35,8 @@ #define ARENA_VM_START (MAX_BPF_JIT_REG + 5) #define check_imm(bits, imm) do { \ - if ((((imm) > 0) && ((imm) >> (bits))) || \ - (((imm) < 0) && (~(imm) >> (bits)))) { \ + if ((((imm) > 0) && ((imm) >> ((bits) - 1))) || \ + (((imm) < 0) && (~(imm) >> ((bits) - 1)))) { \ pr_info("[%2d] imm=%d(0x%x) out of range\n", \ i, imm, imm); \ return -EINVAL; \ |