bpf: Add BPF_FETCH field / create atomic_fetch_add instruction
The BPF_FETCH field can be set in bpf_insn.imm, for BPF_ATOMIC
instructions, in order to have the previous value of the
atomically-modified memory location loaded into the src register
after an atomic op is carried out.
Suggested-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20210114181751.768687-7-jackmanb@google.com
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d8a85f4..6aa1fc9 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -3608,7 +3608,11 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
{
int err;
- if (insn->imm != BPF_ADD) {
+ switch (insn->imm) {
+ case BPF_ADD:
+ case BPF_ADD | BPF_FETCH:
+ break;
+ default:
verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", insn->imm);
return -EINVAL;
}
@@ -3650,8 +3654,20 @@ static int check_atomic(struct bpf_verifier_env *env, int insn_idx, struct bpf_i
return err;
/* check whether we can write into the same memory */
- return check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
- BPF_SIZE(insn->code), BPF_WRITE, -1, true);
+ err = check_mem_access(env, insn_idx, insn->dst_reg, insn->off,
+ BPF_SIZE(insn->code), BPF_WRITE, -1, true);
+ if (err)
+ return err;
+
+ if (!(insn->imm & BPF_FETCH))
+ return 0;
+
+ /* check and record load of old value into src reg */
+ err = check_reg_arg(env, insn->src_reg, DST_OP);
+ if (err)
+ return err;
+
+ return 0;
}
static int __check_stack_boundary(struct bpf_verifier_env *env, u32 regno,
@@ -9528,12 +9544,6 @@ static int do_check(struct bpf_verifier_env *env)
} else if (class == BPF_STX) {
enum bpf_reg_type *prev_dst_type, dst_reg_type;
- if (((BPF_MODE(insn->code) != BPF_MEM &&
- BPF_MODE(insn->code) != BPF_ATOMIC) || insn->imm != 0)) {
- verbose(env, "BPF_STX uses reserved fields\n");
- return -EINVAL;
- }
-
if (BPF_MODE(insn->code) == BPF_ATOMIC) {
err = check_atomic(env, env->insn_idx, insn);
if (err)
@@ -9542,6 +9552,11 @@ static int do_check(struct bpf_verifier_env *env)
continue;
}
+ if (BPF_MODE(insn->code) != BPF_MEM || insn->imm != 0) {
+ verbose(env, "BPF_STX uses reserved fields\n");
+ return -EINVAL;
+ }
+
/* check src1 operand */
err = check_reg_arg(env, insn->src_reg, SRC_OP);
if (err)
