[PATCH bpf v1 01/10] bpf: Mark signal tracepoint siginfo arguments as scalar

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

The signal_generate and signal_deliver tracepoints declare their info
argument as a struct kernel_siginfo pointer. btf_ctx_access() therefore
treats it as a trusted pointer for tp_btf programs.

Signal delivery also uses SEND_SIG_NOINFO and SEND_SIG_PRIV as special
values for this argument. Those values are zero and one respectively,
and are not pointers. A tp_btf program can currently dereference either
value and fault the kernel. In particular, signal_generate can run from
timer interrupt context, turning the fault into a kernel panic.

Record both tracepoints in raw_tp_null_args[] and mark argument one as
a non-pointer. This preserves scalar access to the cookie while rejecting
direct and helper-mediated pointer use. Merely marking it nullable would
not suffice because SEND_SIG_PRIV is nonzero.

Fixes: 838a10bd2ebf ("bpf: Augment raw_tp arguments with PTR_MAYBE_NULL")
Reported-by: Nicholas Carlini <npc@anthropic.com>
Suggested-by: Nicholas Carlini <npc@anthropic.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/btf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index da36d4b9d31a..d6d243c262ea 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6717,6 +6717,9 @@ static const struct bpf_raw_tp_null_args raw_tp_null_args[] = {
 	{ "rxrpc_resend", 0x10 },
 	{ "rxrpc_tq", 0x10 },
 	{ "rxrpc_client", 0x1 },
+	/* signal */
+	{ "signal_generate", 0x20 },
+	{ "signal_deliver", 0x20 },
 	/* skb */
 	{"kfree_skb", 0x1000},
 	/* sunrpc */
-- 
2.53.0