ARG1 = BPF_R1 as it stands, evaluates to regs[BPF_REG_1] = regs[BPF_REG_1]
and thus has no effect. Add a comment instead, explaining what happens and
why it's okay to just remove it. Since from user space side, a tail call is
invoked as a pseudo helper function via bpf_tail_call_proto, the verifier
checks the arguments just like with any other helper function and makes
sure that the first argument (regs[BPF_REG_1])'s type is ARG_PTR_TO_CTX.
Signed-off-by: Daniel Borkmann <dan...@iogearbox.net>
---
kernel/bpf/core.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index c5bedc8..bf38f5e 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -453,7 +453,11 @@ select_insn:
if (unlikely(!prog))
goto out;
- ARG1 = BPF_R1;
+ /* ARG1 at this point is guaranteed to point to CTX from
+ * the verifier side due to the fact that the tail call is
+ * handeled like a helper, that is, bpf_tail_call_proto,
+ * where arg1_type is ARG_PTR_TO_CTX.
+ */
insn = prog->insnsi;
goto select_insn;
out:
--
1.9.3
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
