diff options
| author | Emil Tsalapatis <emil@etsalapatis.com> | 2026-09-22 17:20:24 +0000 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2026-09-22 19:34:04 +0000 |
| commit | f85f5917aa2fbd861c72ea71ecb14a2fa915c3f6 (patch) | |
| tree | 824741e0eef4c22b0649bd065bb6e5a2da3fe263 /include/linux | |
| parent | 1ed69a54d31848618131aaf3311a78adbe78ced0 (diff) | |
bpf: Prevent variable arena/non-arena register contents
The verifier marks ALU instructions that include at least
one arena operand with needs_zext: These instructions are
fixed up after verification to be ALU32 instructions to
ensure that the result is a valid offset into an arena.
However, different code paths may provide two non-arena
64-bit arguments to the same instruction. The result of
the operation in that code path is wrong, since it is
now unexpectedly truncated to 32 bits and zero-extended.
Add logic to the verifier to ensure every instruction either
always has at least one PTR_TO_ARENA argument, or never does.
Since needs_zext already tracks the first scenario, add a
prevent_zext field in bpf_insn_aux to track the latter.
Reject instructions that use arena arguments and have prevent_zext
set, or do not have arena arguments and have needs_zext set.
Fixes: 6082b6c328b5 ("bpf: Recognize addr_space_cast instruction in the verifier.")
Reported-by: Nicholas Carlini <nicholas@carlini.com>
Suggested-by: Nicholas Carlini <nicholas@carlini.com>
Signed-off-by: Emil Tsalapatis <emil@etsalapatis.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://patch.msgid.link/20260922172028.6269-8-emil@etsalapatis.com
Diffstat (limited to 'include/linux')
| -rw-r--r-- | include/linux/bpf_verifier.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h index 6fe8e5dc57aa..b83ec99f1a13 100644 --- a/include/linux/bpf_verifier.h +++ b/include/linux/bpf_verifier.h @@ -680,6 +680,7 @@ struct bpf_insn_aux_data { bool nospec_result; /* result is unsafe under speculation, nospec must follow */ bool zext_dst; /* this insn zero extends dst reg */ bool needs_zext; /* alu op needs to clear upper bits */ + bool prevent_zext; /* alu op cannot be zext (already used with 64-bit scalars) */ bool non_sleepable; /* helper/kfunc may be called from non-sleepable context */ bool is_iter_next; /* bpf_iter_<type>_next() kfunc call */ bool call_with_percpu_alloc_ptr; /* {this,per}_cpu_ptr() with prog percpu alloc */ |