From: Yonghong Song <yonghong.song@linux.dev>
To: bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
"Jose E . Marchesi" <jose.marchesi@oracle.com>,
kernel-team@fb.com, Martin KaFai Lau <martin.lau@kernel.org>
Subject: [PATCH bpf-next v4 22/25] selftests/bpf: Add precision backtracking test for stack arguments
Date: Tue, 12 May 2026 21:51:48 -0700 [thread overview]
Message-ID: <20260513045148.2400087-1-yonghong.song@linux.dev> (raw)
In-Reply-To: <20260513044949.2382019-1-yonghong.song@linux.dev>
Add a test that verifies precision backtracking works correctly
across BPF-to-BPF calls when stack arguments are involved.
The test passes a size value as incoming stack arg (arg6) to a
subprog, which forwards it as the mem__sz parameter (outgoing arg7)
to bpf_kfunc_call_stack_arg_mem. The expected __msg annotations
verify that precision propagates from the kfunc's mem__sz argument
back through the subprog frame to the caller's outgoing stack arg
store.
A companion BTF file (btf__stack_arg_precision.c) provides named
parameter BTF for the __naked subprog via __btf_func_path.
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
.../bpf/prog_tests/stack_arg_precision.c | 10 ++
.../bpf/progs/btf__stack_arg_precision.c | 23 +++
.../selftests/bpf/progs/stack_arg_precision.c | 134 ++++++++++++++++++
3 files changed, 167 insertions(+)
create mode 100644 tools/testing/selftests/bpf/prog_tests/stack_arg_precision.c
create mode 100644 tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c
create mode 100644 tools/testing/selftests/bpf/progs/stack_arg_precision.c
diff --git a/tools/testing/selftests/bpf/prog_tests/stack_arg_precision.c b/tools/testing/selftests/bpf/prog_tests/stack_arg_precision.c
new file mode 100644
index 000000000000..1ab041d66de3
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/stack_arg_precision.c
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include <test_progs.h>
+#include "stack_arg_precision.skel.h"
+
+void test_stack_arg_precision(void)
+{
+ RUN_TESTS(stack_arg_precision);
+}
diff --git a/tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c b/tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c
new file mode 100644
index 000000000000..296fddfe6804
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/btf__stack_arg_precision.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "../test_kmods/bpf_testmod_kfunc.h"
+
+#if defined(__TARGET_ARCH_x86) && defined(__BPF_FEATURE_STACK_ARGUMENT)
+
+long subprog_call_mem_kfunc(long a, long b, long c, long d, long e, long size)
+{
+ char buf[8] = {};
+
+ return bpf_kfunc_call_stack_arg_mem(a, b, c, d, e, buf, size);
+}
+
+#else
+
+long subprog_call_mem_kfunc(void)
+{
+ return 0;
+}
+
+#endif
diff --git a/tools/testing/selftests/bpf/progs/stack_arg_precision.c b/tools/testing/selftests/bpf/progs/stack_arg_precision.c
new file mode 100644
index 000000000000..2a0a344c83ca
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/stack_arg_precision.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */
+
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+#include "../test_kmods/bpf_testmod_kfunc.h"
+#include "bpf_misc.h"
+
+#if defined(__TARGET_ARCH_x86) && defined(__BPF_FEATURE_STACK_ARGUMENT)
+
+/* Force kfunc extern BTF generation for inline asm call below.
+ * Uses its own SEC so it's not included as a .text subprog.
+ * The '?' prefix sets autoload=false so libbpf won't load it.
+ */
+SEC("?tc")
+int __btf_kfunc_gen(struct __sk_buff *ctx)
+{
+ char buf[8] = {};
+
+ return bpf_kfunc_call_stack_arg_mem(0, 0, 0, 0, 0, buf, sizeof(buf));
+}
+
+/*
+ * Test precision backtracking across bpf-to-bpf call for kfunc stack arg.
+ * subprog_call_mem_kfunc receives a size as incoming stack arg (arg6)
+ * and forwards it as mem__sz (arg7) to bpf_kfunc_call_stack_arg_mem.
+ */
+__naked __noinline __used
+static long subprog_call_mem_kfunc(long a, long b, long c, long d, long e, long size)
+{
+ asm volatile (
+ "r1 = *(u64 *)(r11 + 8);" /* r1 = incoming arg6 (size) */
+ "r2 = 0x0807060504030201 ll;" /* r2 = buf contents */
+ "*(u64 *)(r10 - 8) = r2;" /* store buf to stack */
+ "r2 = r10;"
+ "r2 += -8;" /* r2 = &buf */
+ "*(u64 *)(r11 - 8) = r2;" /* outgoing arg6 = buf */
+ "*(u64 *)(r11 - 16) = r1;" /* outgoing arg7 = size */
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "call %[bpf_kfunc_call_stack_arg_mem];"
+ "exit;"
+ :
+ : __imm(bpf_kfunc_call_stack_arg_mem)
+ : __clobber_all
+ );
+}
+
+SEC("tc")
+__description("stack_arg: precision backtracking across bpf2bpf call for kfunc")
+__success
+__log_level(2)
+__flag(BPF_F_TEST_STATE_FREQ)
+__btf_func_path("btf__stack_arg_precision.bpf.o")
+__msg("mark_precise: frame1: last_idx 26 first_idx 13 subseq_idx -1")
+__msg("mark_precise: frame1: regs= stack= before 25: (b7) r5 = 5")
+__msg("mark_precise: frame1: regs= stack= before 24: (b7) r4 = 4")
+__msg("mark_precise: frame1: regs= stack= before 23: (b7) r3 = 3")
+__msg("mark_precise: frame1: regs= stack= before 22: (b7) r2 = 2")
+__msg("mark_precise: frame1: regs= stack= before 21: (b7) r1 = 1")
+__msg("mark_precise: frame1: regs= stack= before 20: (7b) *(u64 *)(r11 -16) = r1")
+__msg("mark_precise: frame1: regs=r1 stack= before 19: (7b) *(u64 *)(r11 -8) = r2")
+__msg("mark_precise: frame1: regs=r1 stack= before 18: (07) r2 += -8")
+__msg("mark_precise: frame1: regs=r1 stack= before 17: (bf) r2 = r10")
+__msg("mark_precise: frame1: regs=r1 stack= before 16: (7b) *(u64 *)(r10 -8) = r2")
+__msg("mark_precise: frame1: regs=r1 stack= before 14: (18) r2 = 0x807060504030201")
+__msg("mark_precise: frame1: regs=r1 stack= before 13: (79) r1 = *(u64 *)(r11 +8)")
+__msg("mark_precise: frame1: parent state regs= stack=: frame1: R10=fp0")
+__msg("mark_precise: frame0: parent state regs= stack=: R10=fp0")
+__msg("mark_precise: frame1: last_idx 11 first_idx 11 subseq_idx 13")
+__msg("mark_precise: frame1: regs= stack= before 11: (85) call pc+1")
+__msg("mark_precise: frame0: parent state regs= stack=: R1=1 R2=2 R3=3 R4=4 R5=5 R10=fp0")
+__msg("mark_precise: frame0: last_idx 9 first_idx 7 subseq_idx 11")
+__msg("mark_precise: frame0: regs= stack= before 9: (05) goto pc+1")
+__msg("mark_precise: frame0: regs= stack= before 8: (7a) *(u64 *)(r11 -8) = 4")
+__msg("mark_precise: frame1: last_idx 26 first_idx 13 subseq_idx -1 ")
+__msg("mark_precise: frame1: regs= stack= before 25: (b7) r5 = 5")
+__msg("mark_precise: frame1: regs= stack= before 24: (b7) r4 = 4")
+__msg("mark_precise: frame1: regs= stack= before 23: (b7) r3 = 3")
+__msg("mark_precise: frame1: regs= stack= before 22: (b7) r2 = 2")
+__msg("mark_precise: frame1: regs= stack= before 21: (b7) r1 = 1")
+__msg("mark_precise: frame1: regs= stack= before 20: (7b) *(u64 *)(r11 -16) = r1")
+__msg("mark_precise: frame1: regs=r1 stack= before 19: (7b) *(u64 *)(r11 -8) = r2")
+__msg("mark_precise: frame1: regs=r1 stack= before 18: (07) r2 += -8")
+__msg("mark_precise: frame1: regs=r1 stack= before 17: (bf) r2 = r10")
+__msg("mark_precise: frame1: regs=r1 stack= before 16: (7b) *(u64 *)(r10 -8) = r2")
+__msg("mark_precise: frame1: regs=r1 stack= before 14: (18) r2 = 0x807060504030201")
+__msg("mark_precise: frame1: regs=r1 stack= before 13: (79) r1 = *(u64 *)(r11 +8)")
+__msg("mark_precise: frame1: parent state regs= stack=: frame1: R10=fp0")
+__msg("mark_precise: frame0: parent state regs= stack=: R10=fp0")
+__msg("mark_precise: frame1: last_idx 11 first_idx 11 subseq_idx 13 ")
+__msg("mark_precise: frame1: regs= stack= before 11: (85) call pc+1")
+__msg("mark_precise: frame0: parent state regs= stack=: R1=1 R2=2 R3=3 R4=4 R5=5 R10=fp0")
+__msg("mark_precise: frame0: last_idx 10 first_idx 10 subseq_idx 11 ")
+__msg("mark_precise: frame0: regs= stack= before 10: (7a) *(u64 *)(r11 -8) = 6")
+__naked void stack_arg_precision_bpf2bpf(void)
+{
+ asm volatile (
+ "call %[bpf_get_prandom_u32];"
+ "r6 = r0;"
+ "r1 = 1;"
+ "r2 = 2;"
+ "r3 = 3;"
+ "r4 = 4;"
+ "r5 = 5;"
+ "if r6 < 2 goto l0_%=;"
+ "*(u64 *)(r11 - 8) = 4;"
+ "goto l1_%=;"
+ "l0_%=:"
+ "*(u64 *)(r11 - 8) = 6;"
+ "l1_%=:"
+ "call subprog_call_mem_kfunc;"
+ "exit;"
+ :: __imm(bpf_get_prandom_u32)
+ : __clobber_all
+ );
+}
+
+#else
+
+SEC("socket")
+__description("stack_arg_precision: not supported, dummy test")
+__success
+int dummy_test(void)
+{
+ return 0;
+}
+
+#endif
+
+char _license[] SEC("license") = "GPL";
--
2.53.0-Meta
next prev parent reply other threads:[~2026-05-13 4:51 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-13 4:49 [PATCH bpf-next v4 00/25] bpf: Support stack arguments for BPF functions and kfuncs Yonghong Song
2026-05-13 4:49 ` [PATCH bpf-next v4 01/25] bpf: Convert bpf_get_spilled_reg macro to static inline function Yonghong Song
2026-05-13 4:50 ` [PATCH bpf-next v4 02/25] bpf: Remove copy_register_state wrapper function Yonghong Song
2026-05-13 4:50 ` [PATCH bpf-next v4 03/25] bpf: Add helper functions for r11-based stack argument insns Yonghong Song
2026-05-13 4:50 ` [PATCH bpf-next v4 04/25] bpf: Set sub->arg_cnt earlier in btf_prepare_func_args() Yonghong Song
2026-05-13 4:50 ` [PATCH bpf-next v4 05/25] bpf: Support stack arguments for bpf functions Yonghong Song
2026-05-13 4:50 ` [PATCH bpf-next v4 06/25] bpf: Refactor jmp history to use dedicated spi/frame fields Yonghong Song
2026-05-13 4:50 ` [PATCH bpf-next v4 07/25] bpf: Add precision marking and backtracking for stack argument slots Yonghong Song
2026-05-13 5:44 ` bot+bpf-ci
2026-05-13 4:50 ` [PATCH bpf-next v4 08/25] bpf: Refactor record_call_access() to extract per-arg logic Yonghong Song
2026-05-13 4:50 ` [PATCH bpf-next v4 09/25] bpf: Use arg_is_fp() in has_fp_args() Yonghong Song
2026-05-13 4:50 ` [PATCH bpf-next v4 10/25] bpf: Extend liveness analysis to track stack argument slots Yonghong Song
2026-05-13 5:44 ` bot+bpf-ci
2026-05-13 4:50 ` [PATCH bpf-next v4 11/25] bpf: Reject stack arguments in non-JITed programs Yonghong Song
2026-05-13 5:33 ` bot+bpf-ci
2026-05-13 4:50 ` [PATCH bpf-next v4 12/25] bpf: Prepare architecture JIT support for stack arguments Yonghong Song
2026-05-13 5:33 ` bot+bpf-ci
2026-05-13 4:50 ` [PATCH bpf-next v4 13/25] bpf: Enable r11 based insns Yonghong Song
2026-05-13 4:51 ` [PATCH bpf-next v4 14/25] bpf: Support stack arguments for kfunc calls Yonghong Song
2026-05-13 4:51 ` [PATCH bpf-next v4 15/25] bpf: Reject stack arguments if tail call reachable Yonghong Song
2026-05-13 5:33 ` bot+bpf-ci
2026-05-13 4:51 ` [PATCH bpf-next v4 16/25] bpf: Disable private stack for x86_64 if stack arguments used Yonghong Song
2026-05-13 5:33 ` bot+bpf-ci
2026-05-13 4:51 ` [PATCH bpf-next v4 17/25] bpf,x86: Implement JIT support for stack arguments Yonghong Song
2026-05-13 4:51 ` [PATCH bpf-next v4 18/25] selftests/bpf: Add tests for BPF function " Yonghong Song
2026-05-13 4:51 ` [PATCH bpf-next v4 19/25] selftests/bpf: Add tests for stack argument validation Yonghong Song
2026-05-13 4:51 ` [PATCH bpf-next v4 20/25] selftests/bpf: Add BTF fixup for __naked subprog parameter names Yonghong Song
2026-05-13 4:51 ` [PATCH bpf-next v4 21/25] selftests/bpf: Add verifier tests for stack argument validation Yonghong Song
2026-05-13 4:51 ` Yonghong Song [this message]
2026-05-13 4:51 ` [PATCH bpf-next v4 23/25] bpf, arm64: Map BPF_REG_0 to x8 instead of x7 Yonghong Song
2026-05-13 4:51 ` [PATCH bpf-next v4 24/25] bpf, arm64: Add JIT support for stack arguments Yonghong Song
2026-05-13 4:52 ` [PATCH bpf-next v4 25/25] selftests/bpf: Enable stack argument tests for arm64 Yonghong Song
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