Commit 1f1e864b authored by Yonghong Song's avatar Yonghong Song Committed by Alexei Starovoitov
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bpf: Handle sign-extenstin ctx member accesses 



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: default avatarEduard Zingerman <eddyz87@gmail.com>
Signed-off-by: default avatarYonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230728011207.3712528-1-yonghong.song@linux.dev


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 8100928c

kernel/bpf/verifier.c

+6 −0
Original line number Diff line number Diff line
@@ -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)