Add inline-asm-based verifier tests that exercise the stack argument
validation logic directly.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 .../selftests/bpf/prog_tests/verifier.c       |   2 +
 .../selftests/bpf/progs/verifier_stack_arg.c  | 122 ++++++++++++++++++
 2 files changed, 124 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_stack_arg.c

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index bcf01cb4cfe4..cbdbcb913bae 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -90,6 +90,7 @@
 #include "verifier_sockmap_mutate.skel.h"
 #include "verifier_spill_fill.skel.h"
 #include "verifier_spin_lock.skel.h"
+#include "verifier_stack_arg.skel.h"
 #include "verifier_stack_ptr.skel.h"
 #include "verifier_store_release.skel.h"
 #include "verifier_subprog_precision.skel.h"
@@ -235,6 +236,7 @@ void test_verifier_sock_addr(void)            { RUN(verifier_sock_addr); }
 void test_verifier_sockmap_mutate(void)       { RUN(verifier_sockmap_mutate); }
 void test_verifier_spill_fill(void)           { RUN(verifier_spill_fill); }
 void test_verifier_spin_lock(void)            { RUN(verifier_spin_lock); }
+void test_verifier_stack_arg(void)            { RUN(verifier_stack_arg); }
 void test_verifier_stack_ptr(void)            { RUN(verifier_stack_ptr); }
 void test_verifier_store_release(void)        { RUN(verifier_store_release); }
 void test_verifier_subprog_precision(void)    { RUN(verifier_subprog_precision); }
diff --git a/tools/testing/selftests/bpf/progs/verifier_stack_arg.c b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
new file mode 100644
index 000000000000..eb1005c771f7
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
@@ -0,0 +1,122 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+#if defined(__TARGET_ARCH_x86) && defined(__BPF_FEATURE_STACK_ARGUMENT)
+
+__noinline __used
+static int subprog_6args(int a, int b, int c, int d, int e, int f)
+{
+	return a + b + c + d + e + f;
+}
+
+__noinline __used
+static int subprog_7args(int a, int b, int c, int d, int e, int f, int g)
+{
+	return a + b + c + d + e + f + g;
+}
+
+SEC("tc")
+__description("stack_arg: subprog with 6 args")
+__success
+__arch_x86_64
+__naked void stack_arg_6args(void)
+{
+	asm volatile (
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u64 *)(r12 - 8) = 6;"
+		"call subprog_6args;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
+SEC("tc")
+__description("stack_arg: two subprogs with >5 args")
+__success
+__arch_x86_64
+__naked void stack_arg_two_subprogs(void)
+{
+	asm volatile (
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u64 *)(r12 - 8) = 10;"
+		"call subprog_6args;"
+		"r6 = r0;"
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u64 *)(r12 - 16) = 30;"
+		"*(u64 *)(r12 - 8) = 20;"
+		"call subprog_7args;"
+		"r0 += r6;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
+SEC("tc")
+__description("stack_arg: gap at offset -8, only wrote -16")
+__failure
+__msg("stack arg#6 not properly initialized")
+__arch_x86_64
+__naked void stack_arg_gap_at_minus8(void)
+{
+	asm volatile (
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u64 *)(r12 - 16) = 30;"
+		"call subprog_7args;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
+SEC("tc")
+__description("stack_arg: misaligned stack arg write")
+__failure
+__msg("stack arg write must be 8 bytes, got 4")
+__arch_x86_64
+__naked void stack_arg_not_written(void)
+{
+	asm volatile (
+		"r1 = 1;"
+		"r2 = 2;"
+		"r3 = 3;"
+		"r4 = 4;"
+		"r5 = 5;"
+		"*(u32 *)(r12 - 4) = 30;"
+		"call subprog_6args;"
+		"exit;"
+		::: __clobber_all
+	);
+}
+
+#else
+
+SEC("socket")
+__description("stack_arg is not supported by compiler or jit, use a dummy test")
+__success
+int dummy_test(void)
+{
+	return 0;
+}
+
+#endif
+
+char _license[] SEC("license") = "GPL";
-- 
2.52.0