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: 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>

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 2f3eebc..7a6945b 100644 (file)
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -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)