[PATCH bpf v2 2/2] selftests/bpf: Test missing and callback stack arguments

[Weiming Shi <bestswngs@gmail.com>]

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(). Expect the verifier to reject the
second r11 load at offset 16.

Also exercise synchronous and asynchronous callbacks whose BTF prototypes
declare a sixth argument. Initialize the outgoing slot at each helper call
site so the programs reach the callback-specific rejection. Keep a valid
six-argument direct call in each program so bpf_fixup_call_args() records
the stack-argument requirement and cannot become an unrelated rejection
fallback.

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

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Assisted-by: LLM
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
Changes in v2:
- Add synchronous bpf_loop callback coverage.
- Add asynchronous bpf_timer callback coverage.
- Add the six-argument callback BTF prototype and initialize the outgoing
  stack slot so both tests reach the callback-specific rejection.

 .../bpf/progs/btf__verifier_stack_arg_order.c |  10 ++
 .../bpf/progs/verifier_stack_arg_order.c      | 121 +++++++++++++++++-
 2 files changed, 130 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c b/tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c
index 99bc115f8380a7..cd0ab034b788ce 100644
--- a/tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c
+++ b/tools/testing/selftests/bpf/progs/btf__verifier_stack_arg_order.c
@@ -25,6 +25,11 @@ void subprog_bad_ptr_7args(long *a, int b, int c, int d, int e, int f, int g)
 {
 }
 
+int callback_6args(long a, long b, long c, long d, long e, long f)
+{
+	return a + b + c + d + e + f;
+}
+
 #else
 
 int subprog_bad_order_6args(void)
@@ -46,4 +51,9 @@ void subprog_bad_ptr_7args(void)
 {
 }
 
+int callback_6args(void)
+{
+	return 0;
+}
+
 #endif
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 c9fe4857da3f55..610c96e8113760 100644
--- a/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg_order.c
@@ -5,6 +5,17 @@
 #include <bpf/bpf_helpers.h>
 #include "bpf_misc.h"
 
+struct timer_value {
+	struct bpf_timer timer;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct timer_value);
+} timer_map SEC(".maps");
+
 #if (defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64)) && \
 	defined(__BPF_FEATURE_STACK_ARGUMENT)
 
@@ -129,6 +140,25 @@ static void subprog_bad_ptr_7args(long *a, int b, int c, int d, int e, int f, in
 	);
 }
 
+__noinline __used __naked
+static int callback_6args(long a, long b, long c, long d, long e, long f)
+{
+	asm volatile ("r0 = *(u64 *)(r11 + 8);"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
+__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 +181,7 @@ __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 +200,95 @@ __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
+	);
+}
+
+SEC("tc")
+__description("stack_arg: synchronous callback with stack args")
+__failure
+__msg("callback subprog cannot have stack args")
+__btf_func_path("btf__verifier_stack_arg_order.bpf.o")
+__naked void stack_arg_sync_callback(void)
+{
+	asm volatile ("r6 = 0;"
+		"*(u64 *)(r11 - 8) = r6;"
+		"r1 = 1;"
+		"r2 = %[callback_6args];"
+		"r3 = 0;"
+		"r4 = 0;"
+		"call %[bpf_loop];"
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u64 *)(r11 - 8) = 6;"
+		"call callback_6args;"
+		"r0 = 0;"
+		"exit;"
+		:
+		: __imm_ptr(callback_6args),
+		  __imm(bpf_loop)
+		: __clobber_common, "r6"
+	);
+}
+
+SEC("tc")
+__description("stack_arg: asynchronous callback with stack args")
+__failure
+__msg("callback subprog cannot have stack args")
+__btf_func_path("btf__verifier_stack_arg_order.bpf.o")
+__naked void stack_arg_async_callback(void)
+{
+	asm volatile ("r1 = 0;"
+		"*(u32 *)(r10 - 4) = r1;"
+		"r1 = %[timer_map] ll;"
+		"r2 = r10;"
+		"r2 += -4;"
+		"call %[bpf_map_lookup_elem];"
+		"if r0 == 0 goto l0_%=;"
+		"r6 = r0;"
+		"r7 = 0;"
+		"*(u64 *)(r11 - 8) = r7;"
+		"r1 = r6;"
+		"r2 = %[callback_6args];"
+		"call %[bpf_timer_set_callback];"
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u64 *)(r11 - 8) = 6;"
+		"call callback_6args;"
+	"l0_%=: r0 = 0;"
+		"exit;"
+		:
+		: __imm_addr(timer_map),
+		  __imm_ptr(callback_6args),
+		  __imm(bpf_map_lookup_elem),
+		  __imm(bpf_timer_set_callback)
+		: __clobber_common, "r6", "r7"
+	);
+}
+
 #else
 
 SEC("socket")
-- 
2.56.0