[PATCH bpf 2/2] selftests/bpf: Test missing caller stack argument slots

[Weiming Shi]

Exercise the path where a static seven-argument subprogram has
unreliable BTF and is called through a bridge with only one initialized
outgoing stack argument. The callee expects two stack arguments, but the
unreliable-BTF path skips check_outgoing_stack_args().

Without the fix, the second r11 load copies an 80-byte bpf_reg_state from
stack_arg_regs[1], past the caller's one-element array. Expect the
verifier to reject that load at offset 16.

The fix also rejects the existing uninitialized-stack-argument test
before the later unreadable-register check. Update that test's expected
diagnostic accordingly.

Assisted-by: LLM
Signed-off-by: Weiming Shi <bestswngs@xxxxxxxxx>
---
 .../bpf/progs/verifier_stack_arg_order.c      | 33 ++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c b/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c
index c9fe4857d..23c7515ea 100644
--- a/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c
@@ -129,6 +129,16 @@ static void subprog_bad_ptr_7args(long *a, int b, int c, int d, int e, int f, in
 	);
 }
 
+__noinline __used __naked
+static void subprog_call_bad_ptr_7args(void)
+{
+	asm volatile ("*(u64 *)(r11 - 8) = 0;"
+		"call subprog_bad_ptr_7args;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
 SEC("tc")
 __description("stack_arg: read without caller write")
 __failure
@@ -151,7 +161,7 @@ __naked void stack_arg_read_without_write_1(void)
 SEC("tc")
 __description("stack_arg: read with not-initialized caller write")
 __failure
-__msg("R0 !read_ok")
+__msg("invalid read from uninitialized stack arg off 8")
 __btf_func_path("btf__verifier_stack_arg_order.bpf.o")
 __naked void stack_arg_read_without_write_2(void)
 {
@@ -170,6 +180,27 @@ __naked void stack_arg_read_without_write_2(void)
 	);
 }
 
+SEC("tc")
+__description("stack_arg: unreliable callee with too few stack args")
+__failure
+__msg("invalid read from uninitialized stack arg off 16")
+__btf_func_path("btf__verifier_stack_arg_order.bpf.o")
+__naked void stack_arg_read_with_short_bridge_write(void)
+{
+	asm volatile ("r1 = 0;"
+		"r2 = 0;"
+		"r3 = 0;"
+		"r4 = 0;"
+		"r5 = 0;"
+		"*(u64 *)(r11 - 8) = 0;"
+		"*(u64 *)(r11 - 16) = 0;"
+		"call subprog_bad_ptr_7args;"
+		"call subprog_call_bad_ptr_7args;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
 #else
 
 SEC("socket")
-- 
2.55.0