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bpf: Handle sign-extenstin ctx member accesses

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Currently, if user accesses a ctx member with signed types,
the compiler will generate an unsigned load followed by
necessary left and right shifts.

With the introduction of sign-extension load, compiler may
just emit a ldsx insn instead. Let us do a final movsx sign
extension to the final unsigned ctx load result to
satisfy original sign extension requirement.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230728011207.3712528-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song 2023-07-27 18:12:07 -07:00 committed by Alexei Starovoitov
parent 8100928c88
commit 1f1e864b65
1 changed files with 6 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

6
kernel/bpf/verifier.c
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@ -17716,6 +17716,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
for (i = 0; i < insn_cnt; i++, insn++) {
bpf_convert_ctx_access_t convert_ctx_access;
u8 mode;
if (insn->code == (BPF_LDX | BPF_MEM | BPF_B) ||
insn->code == (BPF_LDX | BPF_MEM | BPF_H) ||
@ -17797,6 +17798,7 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
ctx_field_size = env->insn_aux_data[i + delta].ctx_field_size;
size = BPF_LDST_BYTES(insn);
mode = BPF_MODE(insn->code);
/* If the read access is a narrower load of the field,
* convert to a 4/8-byte load, to minimum program type specific
@ -17856,6 +17858,10 @@ static int convert_ctx_accesses(struct bpf_verifier_env *env)
(1ULL << size * 8) - 1);
}
}
if (mode == BPF_MEMSX)
insn_buf[cnt++] = BPF_RAW_INSN(BPF_ALU64 | BPF_MOV | BPF_X,
insn->dst_reg, insn->dst_reg,
size * 8, 0);
new_prog = bpf_patch_insn_data(env, i + delta, insn_buf, cnt);
if (!new_prog)