[PATCH v2 bpf-next 2/4] bpf: handle bpf_user_pt_regs_t typedef explicitly for PTR_TO_CTX global arg

[Andrii Nakryiko <andrii@kernel.org>]

Expected canonical argument type for global function arguments
representing PTR_TO_CTX is `bpf_user_pt_regs_t *ctx`. This currently
works on s390x by accident because kernel resolves such typedef to
underlying struct (which is anonymous on s390x), and erroneously
accepting it as expected context type. We are fixing this problem next,
which would break s390x arch, so we need to handle `bpf_user_pt_regs_t`
case explicitly for KPROBE programs.

Fixes: 91cc1a99740e ("bpf: Annotate context types")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/bpf/btf.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index f0ce384aa73e..da958092c969 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -5695,6 +5695,21 @@ bool btf_is_prog_ctx_type(struct bpf_verifier_log *log, const struct btf *btf,
 	const char *tname, *ctx_tname;
 
 	t = btf_type_by_id(btf, t->type);
+
+	/* KPROBE programs allow bpf_user_pt_regs_t typedef, which we need to
+	 * check before we skip all the typedef below.
+	 */
+	if (prog_type == BPF_PROG_TYPE_KPROBE) {
+		while (btf_type_is_modifier(t) && !btf_type_is_typedef(t))
+			t = btf_type_by_id(btf, t->type);
+
+		if (btf_type_is_typedef(t)) {
+			tname = btf_name_by_offset(btf, t->name_off);
+			if (tname && strcmp(tname, "bpf_user_pt_regs_t") == 0)
+				return true;
+		}
+	}
+
 	while (btf_type_is_modifier(t))
 		t = btf_type_by_id(btf, t->type);
 	if (!btf_type_is_struct(t)) {
-- 
2.39.3