From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from 66-220-155-178.mail-mxout.facebook.com (66-220-155-178.mail-mxout.facebook.com [66.220.155.178]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 97303346791 for ; Thu, 7 May 2026 21:32:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=66.220.155.178 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778189525; cv=none; b=UoePY53VLqVMgVhtQr7nCBeNTVYexbYIKelYF+a/1rxeT5r6BppuTBeeQEE/F4T3ufz4YFFZVc7Tsxhxj6KEWXZr45QPIfql7+QNCdGFK8yKCFCvUBz8gJUJwIW9KR1iC2SRf/dJgNZ6qbI5IMk46ONcFgx16UuZDxDz+fTEksE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778189525; c=relaxed/simple; bh=tICgs89gwFedXCkQmUBAAvKS7pDmkYjnihvfoiZUUj0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=bwmzlQKhdd6dKjp1seQOAMbvcVV9i+jmchzt78xAoreTYUrvymUkaJ9GDItZlzuHFW0I5/a8q97gIZ8uO3alPfaDkJxJItZ0uUS8BDn/CdMjGXk6xGm1jj7UfIpnwKxSMcbTxWZxKDqwiwvrtrqvOEKBRb22GrPwBgRaT723QCI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=fail smtp.mailfrom=linux.dev; arc=none smtp.client-ip=66.220.155.178 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=linux.dev Received: by devvm16039.vll0.facebook.com (Postfix, from userid 128203) id 039B292BBF885; Thu, 7 May 2026 14:31:50 -0700 (PDT) From: Yonghong Song To: bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , "Jose E . Marchesi" , kernel-team@fb.com, Martin KaFai Lau Subject: [PATCH bpf-next v2 20/23] selftests/bpf: Add precision backtracking test for stack arguments Date: Thu, 7 May 2026 14:31:50 -0700 Message-ID: <20260507213150.1139244-1-yonghong.song@linux.dev> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260507212942.1122000-1-yonghong.song@linux.dev> References: <20260507212942.1122000-1-yonghong.song@linux.dev> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable 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 bounds-checks it and 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 --- .../bpf/prog_tests/stack_arg_precision.c | 10 ++ .../bpf/progs/btf__stack_arg_precision.c | 23 +++ .../selftests/bpf/progs/stack_arg_precision.c | 137 ++++++++++++++++++ 3 files changed, 170 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/stack_arg_prec= ision.c create mode 100644 tools/testing/selftests/bpf/progs/btf__stack_arg_prec= ision.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 +#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 +#include +#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] =3D {}; + + 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/to= ols/testing/selftests/bpf/progs/stack_arg_precision.c new file mode 100644 index 000000000000..c94905f07dcc --- /dev/null +++ b/tools/testing/selftests/bpf/progs/stack_arg_precision.c @@ -0,0 +1,137 @@ +// SPDX-License-Identifier: GPL-2.0 +/* Copyright (c) 2026 Meta Platforms, Inc. and affiliates. */ + +#include +#include +#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=3Dfalse so libbpf won't load it. + */ +SEC("?tc") +int __btf_kfunc_gen(struct __sk_buff *ctx) +{ + char buf[8] =3D {}; + + 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 ar= g. + * subprog_call_mem_kfunc receives a size as incoming stack arg (arg6), + * bounds-checks it, then passes it as mem__sz (arg7) to + * bpf_kfunc_call_stack_arg_mem. + * + * 1+2+3+4+5+(1+2+3+4) =3D 25 + */ +__naked __noinline __used +static long subprog_call_mem_kfunc(long a, long b, long c, long d, long = e, long size) +{ + asm volatile ( + "r1 =3D *(u64 *)(r11 + 8);" /* r1 =3D incoming arg6 (size) */ + "r2 =3D 0x0807060504030201 ll;" /* r2 =3D buf contents */ + "*(u64 *)(r10 - 8) =3D r2;" /* store buf to stack */ + "r2 =3D r10;" + "r2 +=3D -8;" /* r2 =3D &buf */ + "*(u64 *)(r11 - 8) =3D r2;" /* outgoing arg6 =3D buf */ + "*(u64 *)(r11 - 16) =3D r1;" /* outgoing arg7 =3D size */ + "r1 =3D 1;" + "r2 =3D 2;" + "r3 =3D 3;" + "r4 =3D 4;" + "r5 =3D 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 __retval(25) +__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=3D stack=3D before 25: (b7) r5 =3D 5") +__msg("mark_precise: frame1: regs=3D stack=3D before 24: (b7) r4 =3D 4") +__msg("mark_precise: frame1: regs=3D stack=3D before 23: (b7) r3 =3D 3") +__msg("mark_precise: frame1: regs=3D stack=3D before 22: (b7) r2 =3D 2") +__msg("mark_precise: frame1: regs=3D stack=3D before 21: (b7) r1 =3D 1") +__msg("mark_precise: frame1: regs=3D stack=3D before 20: (7b) *(u64 *)(r= 11 -16) =3D r1") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 19: (7b) *(u64 *)= (r11 -8) =3D r2") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 18: (07) r2 +=3D = -8") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 17: (bf) r2 =3D r= 10") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 16: (7b) *(u64 *)= (r10 -8) =3D r2") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 14: (18) r2 =3D 0= x807060504030201") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 13: (79) r1 =3D *= (u64 *)(r11 +8)") +__msg("mark_precise: frame1: parent state regs=3D stack=3D: frame1: R10= =3Dfp0") +__msg("mark_precise: frame0: parent state regs=3D stack=3D: R10=3Dfp0") +__msg("mark_precise: frame1: last_idx 11 first_idx 11 subseq_idx 13") +__msg("mark_precise: frame1: regs=3D stack=3D before 11: (85) call pc+1"= ) +__msg("mark_precise: frame0: parent state regs=3D stack=3D: R1=3D1 R2=3D= 2 R3=3D3 R4=3D4 R5=3D5 R10=3Dfp0") +__msg("mark_precise: frame0: last_idx 9 first_idx 7 subseq_idx 11") +__msg("mark_precise: frame0: regs=3D stack=3D before 9: (05) goto pc+1") +__msg("mark_precise: frame0: regs=3D stack=3D before 8: (7a) *(u64 *)(r1= 1 -8) =3D 4") +__msg("mark_precise: frame1: last_idx 26 first_idx 13 subseq_idx -1 ") +__msg("mark_precise: frame1: regs=3D stack=3D before 25: (b7) r5 =3D 5") +__msg("mark_precise: frame1: regs=3D stack=3D before 24: (b7) r4 =3D 4") +__msg("mark_precise: frame1: regs=3D stack=3D before 23: (b7) r3 =3D 3") +__msg("mark_precise: frame1: regs=3D stack=3D before 22: (b7) r2 =3D 2") +__msg("mark_precise: frame1: regs=3D stack=3D before 21: (b7) r1 =3D 1") +__msg("mark_precise: frame1: regs=3D stack=3D before 20: (7b) *(u64 *)(r= 11 -16) =3D r1") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 19: (7b) *(u64 *)= (r11 -8) =3D r2") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 18: (07) r2 +=3D = -8") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 17: (bf) r2 =3D r= 10") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 16: (7b) *(u64 *)= (r10 -8) =3D r2") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 14: (18) r2 =3D 0= x807060504030201") +__msg("mark_precise: frame1: regs=3Dr1 stack=3D before 13: (79) r1 =3D *= (u64 *)(r11 +8)") +__msg("mark_precise: frame1: parent state regs=3D stack=3D: frame1: R10= =3Dfp0") +__msg("mark_precise: frame0: parent state regs=3D stack=3D: R10=3Dfp0") +__msg("mark_precise: frame1: last_idx 11 first_idx 11 subseq_idx 13 ") +__msg("mark_precise: frame1: regs=3D stack=3D before 11: (85) call pc+1"= ) +__msg("mark_precise: frame0: parent state regs=3D stack=3D: R1=3D1 R2=3D= 2 R3=3D3 R4=3D4 R5=3D5 R10=3Dfp0") +__msg("mark_precise: frame0: last_idx 10 first_idx 10 subseq_idx 11 ") +__msg("mark_precise: frame0: regs=3D stack=3D before 10: (7a) *(u64 *)(r= 11 -8) =3D 6") +__naked void stack_arg_precision_bpf2bpf(void) +{ + asm volatile ( + "call %[bpf_get_prandom_u32];" + "r6 =3D r0;" + "r1 =3D 1;" + "r2 =3D 2;" + "r3 =3D 3;" + "r4 =3D 4;" + "r5 =3D 5;" + "if r6 < 2 goto l0_%=3D;" + "*(u64 *)(r11 - 8) =3D 4;" + "goto l1_%=3D;" + "l0_%=3D:" + "*(u64 *)(r11 - 8) =3D 6;" + "l1_%=3D:" + "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") =3D "GPL"; --=20 2.53.0-Meta