On 6/9/24 12:31 AM, Leon Hwang wrote:
It's confusing to inspect 'prog->aux->tail_call_reachable' with drgn[0],
when bpf prog has tail call but 'tail_call_reachable' is false.
This patch corrects 'tail_call_reachable' when bpf prog has tail call.
[0] https://github.com/osandov/drgn
Signed-off-by: Leon Hwang <hffilwlqm@xxxxxxxxx>
---
kernel/bpf/verifier.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 81a3d2ced78d5..d7045676246a7 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2982,8 +2982,10 @@ static int check_subprogs(struct bpf_verifier_env *env)
if (code == (BPF_JMP | BPF_CALL) &&
insn[i].src_reg == 0 &&
- insn[i].imm == BPF_FUNC_tail_call)
+ insn[i].imm == BPF_FUNC_tail_call) {
subprog[cur_subprog].has_tail_call = true;
+ subprog[cur_subprog].tail_call_reachable = true;
This tail_call_reachable is handled in jit. For example, in arch/x86/net/bpf_jit_comp.c:
static void detect_reg_usage(struct bpf_insn *insn, int insn_cnt,
bool *regs_used, bool *tail_call_seen)
{
int i;
for (i = 1; i <= insn_cnt; i++, insn++) {
if (insn->code == (BPF_JMP | BPF_TAIL_CALL))
*tail_call_seen = true;
if (insn->dst_reg == BPF_REG_6 || insn->src_reg == BPF_REG_6)
regs_used[0] = true;
if (insn->dst_reg == BPF_REG_7 || insn->src_reg == BPF_REG_7)
regs_used[1] = true;
if (insn->dst_reg == BPF_REG_8 || insn->src_reg == BPF_REG_8)
regs_used[2] = true;
if (insn->dst_reg == BPF_REG_9 || insn->src_reg == BPF_REG_9)
regs_used[3] = true;
}
}
and
detect_reg_usage(insn, insn_cnt, callee_regs_used,
&tail_call_seen);
/* tail call's presence in current prog implies it is reachable */
tail_call_reachable |= tail_call_seen;
I didn't check other architectures. If other arch is similar to x86 w.r.t.
tail_call_reachable marking, your change looks good. But you should also
make changes in jit to remove those redundent checking.
+ }
if (BPF_CLASS(code) == BPF_LD &&
(BPF_MODE(code) == BPF_ABS || BPF_MODE(code) == BPF_IND))
subprog[cur_subprog].has_ld_abs = true;
base-commit: 2c6987105026a4395935a3db665c54eb1bafe782
