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| author | Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2025-09-23 11:01:49 +0000 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2025-09-23 12:00:22 -0700 |
| commit | a91ae3c89311648cbaa9b46b860e4f76004a24b8 (patch) | |
| tree | eb70a89b901b3de88d52d81bc9536db2a337c5fc /kernel/bpf | |
| parent | Merge branch 'bpf-introduce-deferred-task-context-execution' (diff) | |
| download | linux-a91ae3c89311648cbaa9b46b860e4f76004a24b8.tar.gz linux-a91ae3c89311648cbaa9b46b860e4f76004a24b8.zip | |
bpf, x86: Add support for signed arena loads
Currently, signed load instructions into arena memory are unsupported.
The compiler is free to generate these, and on GCC-14 we see a
corresponding error when it happens. The hurdle in supporting them is
deciding which unused opcode to use to mark them for the JIT's own
consumption. After much thinking, it appears 0xc0 / BPF_NOSPEC can be
combined with load instructions to identify signed arena loads. Use
this to recognize and JIT them appropriately, and remove the verifier
side limitation on the program if the JIT supports them.
Co-developed-by: Puranjay Mohan <puranjay@kernel.org>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
Link: https://lore.kernel.org/r/20250923110157.18326-2-puranjay@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'kernel/bpf')
| -rw-r--r-- | kernel/bpf/verifier.c | 11 |
1 files changed, 8 insertions, 3 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index ceeb0ffe7d67..164199237176 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -21379,10 +21379,14 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env) continue; case PTR_TO_ARENA: if (BPF_MODE(insn->code) == BPF_MEMSX) { - verbose(env, "sign extending loads from arena are not supported yet\n"); - return -EOPNOTSUPP; + if (!bpf_jit_supports_insn(insn, true)) { + verbose(env, "sign extending loads from arena are not supported yet\n"); + return -EOPNOTSUPP; + } + insn->code = BPF_CLASS(insn->code) | BPF_PROBE_MEM32SX | BPF_SIZE(insn->code); + } else { + insn->code = BPF_CLASS(insn->code) | BPF_PROBE_MEM32 | BPF_SIZE(insn->code); } - insn->code = BPF_CLASS(insn->code) | BPF_PROBE_MEM32 | BPF_SIZE(insn->code); env->prog->aux->num_exentries++; continue; default: @@ -21588,6 +21592,7 @@ static int jit_subprogs(struct bpf_verifier_env *env) if (BPF_CLASS(insn->code) == BPF_LDX && (BPF_MODE(insn->code) == BPF_PROBE_MEM || BPF_MODE(insn->code) == BPF_PROBE_MEM32 || + BPF_MODE(insn->code) == BPF_PROBE_MEM32SX || BPF_MODE(insn->code) == BPF_PROBE_MEMSX)) num_exentries++; if ((BPF_CLASS(insn->code) == BPF_STX || |