[PATCH bpf-next v2 11/11] selftests/bpf: Add verifier tests for stack argument validation

Yonghong Song
2026-04-05T16:55:12Z

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 | 302 ++++++++++++++++++
2 files changed, 304 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 1ac366fd4dae..f39ed1f28a7b 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"
@@ -236,6 +237,7 @@ 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..921a9b3bee7f
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/verifier_stack_arg.c
@@ -0,0 +1,302 @@
+// 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"
+
+struct {
+ __uint(type, BPF_MAP_TYPE_HASH);
+ __uint(max_entries, 1);
+ __type(key, long long);
+ __type(value, long long);
+} map_hash_8b SEC(".maps");
+
+#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: read from uninitialized stack arg slot")
+__failure
+__arch_x86_64
+__msg("invalid read from stack arg")
+__naked void stack_arg_read_uninitialized(void)
+{
+ asm volatile (
+ "r0 = *(u64 *)(r12 - 8);"
+ "r0 = 0;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: gap at offset -8, only wrote -16")
+__failure
+__arch_x86_64
+__msg("stack arg#6 not properly initialized")
+__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: incorrect size of stack arg write")
+__failure
+__arch_x86_64
+__msg("stack arg write must be 8 bytes, got 4")
+__naked void stack_arg_not_written(void)
+{
+ asm volatile (
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "*(u32 *)(r12 - 8) = 30;"
+ "call subprog_6args;"
+ "exit;"
+ ::: __clobber_all
+ );
+}
+
+__noinline __used
+static long subprog_stack_arg_pruning_deref(int a, int b, int c, int d, int e, int f)
+{
+ long local = 0, *p, *ptr;
+
+ if (a <= 3) {
+ /* Overwrite the stack arg slot with a pointer to local */
+ p = &local;
+ asm volatile ("*(u64 *)(r12 - 8) = %[p];" :: [p] "r"(p) : "memory");
+ }
+
+ /* Read back the (possibly overwritten) stack arg slot */
+ asm volatile ("%[ptr] = *(u64 *)(r12 - 8);" : [ptr] "=r"(ptr) :: "memory");
+
+ /* Deref: safe for PTR_TO_STACK, unsafe for scalar */
+ return *ptr;
+}
+
+SEC("tc")
+__description("stack_arg: pruning with different stack arg types")
+__failure
+__flag(BPF_F_TEST_STATE_FREQ)
+__arch_x86_64
+__msg("invalid mem access 'scalar'")
+__naked void stack_arg_pruning_type_mismatch(void)
+{
+ asm volatile (
+ "call %[bpf_get_prandom_u32];"
+ "r1 = r0;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "*(u64 *)(r12 - 8) = 42;"
+ "call subprog_stack_arg_pruning_deref;"
+ "exit;"
+ :: __imm(bpf_get_prandom_u32)
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: release_reference invalidates stack arg slot")
+__failure
+__arch_x86_64
+__msg("R0 invalid mem access 'scalar'")
+__naked void stack_arg_release_ref(void)
+{
+ asm volatile (
+ "r6 = r1;"
+ /* struct bpf_sock_tuple tuple = {} */
+ "r2 = 0;"
+ "*(u32 *)(r10 - 8) = r2;"
+ "*(u64 *)(r10 - 16) = r2;"
+ "*(u64 *)(r10 - 24) = r2;"
+ "*(u64 *)(r10 - 32) = r2;"
+ "*(u64 *)(r10 - 40) = r2;"
+ "*(u64 *)(r10 - 48) = r2;"
+ /* sk = bpf_sk_lookup_tcp(ctx, &tuple, sizeof(tuple), 0, 0) */
+ "r1 = r6;"
+ "r2 = r10;"
+ "r2 += -48;"
+ "r3 = %[sizeof_bpf_sock_tuple];"
+ "r4 = 0;"
+ "r5 = 0;"
+ "call %[bpf_sk_lookup_tcp];"
+ /* r0 = sk (PTR_TO_SOCK_OR_NULL) */
+ "if r0 == 0 goto l0_%=;"
+ /* spill sk to stack arg slot */
+ "*(u64 *)(r12 - 8) = r0;"
+ /* release the reference */
+ "r1 = r0;"
+ "call %[bpf_sk_release];"
+ /* r0 and stack arg slot (r12 - 8) should be invalid now. */
+ "r0 = *(u64 *)(r12 - 8);"
+ "r0 = *(u8 *)(r0 + 0);"
+ "l0_%=:"
+ "r0 = 0;"
+ "exit;"
+ :
+ : __imm(bpf_sk_lookup_tcp),
+ __imm(bpf_sk_release),
+ __imm_const(sizeof_bpf_sock_tuple, sizeof(struct bpf_sock_tuple))
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: pkt pointer in stack arg slot invalidated after pull_data")
+__failure
+__arch_x86_64
+__msg("R0 invalid mem access 'scalar'")
+__naked void stack_arg_stale_pkt_ptr(void)
+{
+ asm volatile (
+ "r6 = r1;"
+ "r7 = *(u32 *)(r6 + %[__sk_buff_data]);"
+ "r8 = *(u32 *)(r6 + %[__sk_buff_data_end]);"
+ /* check pkt has at least 1 byte */
+ "r0 = r7;"
+ "r0 += 1;"
+ "if r0 > r8 goto l0_%=;"
+ /* spill valid pkt pointer to stack arg slot */
+ "*(u64 *)(r12 - 8) = r7;"
+ /* bpf_skb_pull_data(skb, 0) — invalidates all pkt pointers */
+ "r1 = r6;"
+ "r2 = 0;"
+ "call %[bpf_skb_pull_data];"
+ /* read back the stale pkt pointer from stack arg slot */
+ "r0 = *(u64 *)(r12 - 8);"
+ /* dereferencing stale pkt pointer should fail */
+ "r0 = *(u8 *)(r0 + 0);"
+ "l0_%=:"
+ "r0 = 0;"
+ "exit;"
+ :
+ : __imm(bpf_skb_pull_data),
+ __imm_const(__sk_buff_data, offsetof(struct __sk_buff, data)),
+ __imm_const(__sk_buff_data_end, offsetof(struct __sk_buff, data_end))
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: null propagation rejects deref on null branch")
+__failure
+__arch_x86_64
+__msg("R1 invalid mem access 'scalar'")
+__naked void stack_arg_null_propagation_fail(void)
+{
+ asm volatile (
+ "r1 = 0;"
+ "*(u64 *)(r10 - 8) = r1;"
+ /* r0 = bpf_map_lookup_elem(&map_hash_8b, &key) */
+ "r2 = r10;"
+ "r2 += -8;"
+ "r1 = %[map_hash_8b] ll;"
+ "call %[bpf_map_lookup_elem];"
+ /* spill PTR_TO_MAP_VALUE_OR_NULL to stack arg slot */
+ "*(u64 *)(r12 - 8) = r0;"
+ /* null check on r0 */
+ "if r0 != 0 goto l0_%=;"
+ /*
+ * on null branch, stack arg slot should be null (scalar 0).
+ * read it back and dereference should fail.
+ */
+ "r1 = *(u64 *)(r12 - 8);"
+ "r0 = *(u64 *)(r1 + 0);"
+ "l0_%=:"
+ "r0 = 0;"
+ "exit;"
+ :
+ : __imm(bpf_map_lookup_elem),
+ __imm_addr(map_hash_8b)
+ : __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