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Date: Wed, 7 Sep 2022 20:30:41 +0200
From: Benjamin Tissoires <benjamin.tissoires@...hat.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Kumar Kartikeya Dwivedi <memxor@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>,
bpf <bpf@...r.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH bpf-next v11 4/7] selftests/bpf: add test for accessing
ctx from syscall program type
On Wed, Sep 7, 2022 at 8:09 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Wed, Sep 7, 2022 at 10:46 AM Kumar Kartikeya Dwivedi
> <memxor@...il.com> wrote:
> >
> > On Tue, 6 Sept 2022 at 17:13, Benjamin Tissoires
> > <benjamin.tissoires@...hat.com> wrote:
> > >
> > > We need to also export the kfunc set to the syscall program type,
> > > and then add a couple of eBPF programs that are testing those calls.
> > >
> > > The first one checks for valid access, and the second one is OK
> > > from a static analysis point of view but fails at run time because
> > > we are trying to access outside of the allocated memory.
> > >
> > > Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> > >
> > > ---
> >
> > CI is failing for test_progs-no_alu32:
> > https://github.com/kernel-patches/bpf/runs/8220916615?check_suite_focus=true
> >
> > >
> > > changes in v11:
> > > - use new way of declaring tests
> > >
> > > changes in v10:
> > > - use new definitions for tests in an array
> > > - add a new kfunc syscall_test_null_fail test
> > >
> > > no changes in v9
> > >
> > > no changes in v8
> > >
> > > changes in v7:
> > > - add 1 more case to ensure we can read the entire sizeof(ctx)
> > > - add a test case for when the context is NULL
> > >
> > > new in v6
> > > ---
> > > net/bpf/test_run.c | 1 +
> > > .../selftests/bpf/prog_tests/kfunc_call.c | 143 +++++++++++++++++-
> > > .../selftests/bpf/progs/kfunc_call_fail.c | 39 +++++
> > > .../selftests/bpf/progs/kfunc_call_test.c | 38 +++++
> > > 4 files changed, 214 insertions(+), 7 deletions(-)
> > > create mode 100644 tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> > >
> > > diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> > > index 25d8ecf105aa..f16baf977a21 100644
> > > --- a/net/bpf/test_run.c
> > > +++ b/net/bpf/test_run.c
> > > @@ -1634,6 +1634,7 @@ static int __init bpf_prog_test_run_init(void)
> > >
> > > ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS, &bpf_prog_test_kfunc_set);
> > > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &bpf_prog_test_kfunc_set);
> > > + ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL, &bpf_prog_test_kfunc_set);
> > > return ret ?: register_btf_id_dtor_kfuncs(bpf_prog_test_dtor_kfunc,
> > > ARRAY_SIZE(bpf_prog_test_dtor_kfunc),
> > > THIS_MODULE);
> > > diff --git a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > > index 9dfbe5355a2d..d5881c3331a8 100644
> > > --- a/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > > +++ b/tools/testing/selftests/bpf/prog_tests/kfunc_call.c
> > > @@ -2,6 +2,7 @@
> > > /* Copyright (c) 2021 Facebook */
> > > #include <test_progs.h>
> > > #include <network_helpers.h>
> > > +#include "kfunc_call_fail.skel.h"
> > > #include "kfunc_call_test.skel.h"
> > > #include "kfunc_call_test.lskel.h"
> > > #include "kfunc_call_test_subprog.skel.h"
> > > @@ -10,37 +11,96 @@
> > >
> > > #include "cap_helpers.h"
> > >
> > > +static size_t log_buf_sz = 1048576; /* 1 MB */
> > > +static char obj_log_buf[1048576];
> > > +
> > > +enum kfunc_test_type {
> > > + tc_test = 0,
> > > + syscall_test,
> > > + syscall_null_ctx_test,
> > > +};
> > > +
> > > struct kfunc_test_params {
> > > const char *prog_name;
> > > unsigned long lskel_prog_desc_offset;
> > > int retval;
> > > + enum kfunc_test_type test_type;
> > > + const char *expected_err_msg;
> > > };
> > >
> > > -#define TC_TEST(name, __retval) \
> > > +#define __BPF_TEST_SUCCESS(name, __retval, type) \
> > > { \
> > > .prog_name = #name, \
> > > .lskel_prog_desc_offset = offsetof(struct kfunc_call_test_lskel, progs.name), \
> > > .retval = __retval, \
> > > + .test_type = type, \
> > > + .expected_err_msg = NULL, \
> > > + }
> > > +
> > > +#define __BPF_TEST_FAIL(name, __retval, type, error_msg) \
> > > + { \
> > > + .prog_name = #name, \
> > > + .lskel_prog_desc_offset = 0 /* unused when test is failing */, \
> > > + .retval = __retval, \
> > > + .test_type = type, \
> > > + .expected_err_msg = error_msg, \
> > > }
> > >
> > > +#define TC_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, tc_test)
> > > +#define SYSCALL_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, syscall_test)
> > > +#define SYSCALL_NULL_CTX_TEST(name, retval) __BPF_TEST_SUCCESS(name, retval, syscall_null_ctx_test)
> > > +
> > > +#define SYSCALL_NULL_CTX_FAIL(name, retval, error_msg) \
> > > + __BPF_TEST_FAIL(name, retval, syscall_null_ctx_test, error_msg)
> > > +
> > > static struct kfunc_test_params kfunc_tests[] = {
> > > + /* failure cases:
> > > + * if retval is 0 -> the program will fail to load and the error message is an error
> > > + * if retval is not 0 -> the program can be loaded but running it will gives the
> > > + * provided return value. The error message is thus the one
> > > + * from a successful load
> > > + */
> > > + SYSCALL_NULL_CTX_FAIL(kfunc_syscall_test_fail, -EINVAL, "processed 4 insns"),
> > > + SYSCALL_NULL_CTX_FAIL(kfunc_syscall_test_null_fail, -EINVAL, "processed 4 insns"),
> > > +
> > > + /* success cases */
> > > TC_TEST(kfunc_call_test1, 12),
> > > TC_TEST(kfunc_call_test2, 3),
> > > TC_TEST(kfunc_call_test_ref_btf_id, 0),
> > > + SYSCALL_TEST(kfunc_syscall_test, 0),
> > > + SYSCALL_NULL_CTX_TEST(kfunc_syscall_test_null, 0),
> > > +};
> > > +
> > > +struct syscall_test_args {
> > > + __u8 data[16];
> > > + size_t size;
> > > };
> > >
> > > static void verify_success(struct kfunc_test_params *param)
> > > {
> > > struct kfunc_call_test_lskel *lskel = NULL;
> > > + LIBBPF_OPTS(bpf_test_run_opts, topts);
> > > struct bpf_prog_desc *lskel_prog;
> > > struct kfunc_call_test *skel;
> > > struct bpf_program *prog;
> > > int prog_fd, err;
> > > - LIBBPF_OPTS(bpf_test_run_opts, topts,
> > > - .data_in = &pkt_v4,
> > > - .data_size_in = sizeof(pkt_v4),
> > > - .repeat = 1,
> > > - );
> > > + struct syscall_test_args args = {
> > > + .size = 10,
> > > + };
> > > +
> > > + switch (param->test_type) {
> > > + case syscall_test:
> > > + topts.ctx_in = &args;
> > > + topts.ctx_size_in = sizeof(args);
> > > + /* fallthrough */
> > > + case syscall_null_ctx_test:
> > > + break;
> > > + case tc_test:
> > > + topts.data_in = &pkt_v4;
> > > + topts.data_size_in = sizeof(pkt_v4);
> > > + topts.repeat = 1;
> > > + break;
> > > + }
> > >
> > > /* first test with normal libbpf */
> > > skel = kfunc_call_test__open_and_load();
> > > @@ -79,6 +139,72 @@ static void verify_success(struct kfunc_test_params *param)
> > > kfunc_call_test_lskel__destroy(lskel);
> > > }
> > >
> > > +static void verify_fail(struct kfunc_test_params *param)
> > > +{
> > > + LIBBPF_OPTS(bpf_object_open_opts, opts);
> > > + LIBBPF_OPTS(bpf_test_run_opts, topts);
> > > + struct bpf_program *prog;
> > > + struct kfunc_call_fail *skel;
> > > + int prog_fd, err;
> > > + struct syscall_test_args args = {
> > > + .size = 10,
> > > + };
> > > +
> > > + opts.kernel_log_buf = obj_log_buf;
> > > + opts.kernel_log_size = log_buf_sz;
> > > + opts.kernel_log_level = 1;
> > > +
> > > + switch (param->test_type) {
> > > + case syscall_test:
> > > + topts.ctx_in = &args;
> > > + topts.ctx_size_in = sizeof(args);
> > > + /* fallthrough */
> > > + case syscall_null_ctx_test:
> > > + break;
> > > + case tc_test:
> > > + topts.data_in = &pkt_v4;
> > > + topts.data_size_in = sizeof(pkt_v4);
> > > + break;
> > > + topts.repeat = 1;
> > > + }
> > > +
> > > + skel = kfunc_call_fail__open_opts(&opts);
> > > + if (!ASSERT_OK_PTR(skel, "kfunc_call_fail__open_opts"))
> > > + goto cleanup;
> > > +
> > > + prog = bpf_object__find_program_by_name(skel->obj, param->prog_name);
> > > + if (!ASSERT_OK_PTR(prog, "bpf_object__find_program_by_name"))
> > > + goto cleanup;
> > > +
> > > + bpf_program__set_autoload(prog, true);
> > > +
> > > + err = kfunc_call_fail__load(skel);
> > > + if (!param->retval) {
> > > + /* the verifier is supposed to complain and refuses to load */
> > > + if (!ASSERT_ERR(err, "unexpected load success"))
> > > + goto out_err;
> > > +
> > > + } else {
> > > + /* the program is loaded but must dynamically fail */
> > > + if (!ASSERT_OK(err, "unexpected load error"))
> > > + goto out_err;
> > > +
> > > + prog_fd = bpf_program__fd(prog);
> > > + err = bpf_prog_test_run_opts(prog_fd, &topts);
> > > + if (!ASSERT_EQ(err, param->retval, param->prog_name))
> > > + goto out_err;
> > > + }
> > > +
> > > +out_err:
> > > + if (!ASSERT_OK_PTR(strstr(obj_log_buf, param->expected_err_msg), "expected_err_msg")) {
> > > + fprintf(stderr, "Expected err_msg: %s\n", param->expected_err_msg);
> > > + fprintf(stderr, "Verifier output: %s\n", obj_log_buf);
> > > + }
> > > +
> > > +cleanup:
> > > + kfunc_call_fail__destroy(skel);
> > > +}
> > > +
> > > static void test_main(void)
> > > {
> > > int i;
> > > @@ -87,7 +213,10 @@ static void test_main(void)
> > > if (!test__start_subtest(kfunc_tests[i].prog_name))
> > > continue;
> > >
> > > - verify_success(&kfunc_tests[i]);
> > > + if (!kfunc_tests[i].expected_err_msg)
> > > + verify_success(&kfunc_tests[i]);
> > > + else
> > > + verify_fail(&kfunc_tests[i]);
> > > }
> > > }
> > >
> > > diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_fail.c b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> > > new file mode 100644
> > > index 000000000000..4168027f2ab1
> > > --- /dev/null
> > > +++ b/tools/testing/selftests/bpf/progs/kfunc_call_fail.c
> > > @@ -0,0 +1,39 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/* Copyright (c) 2021 Facebook */
> > > +#include <vmlinux.h>
> > > +#include <bpf/bpf_helpers.h>
> > > +
> > > +extern void bpf_kfunc_call_test_mem_len_pass1(void *mem, int len) __ksym;
> > > +
> > > +struct syscall_test_args {
> > > + __u8 data[16];
> > > + size_t size;
> > > +};
> > > +
> > > +SEC("?syscall")
> > > +int kfunc_syscall_test_fail(struct syscall_test_args *args)
> > > +{
> > > + bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(*args) + 1);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +SEC("?syscall")
> > > +int kfunc_syscall_test_null_fail(struct syscall_test_args *args)
> > > +{
> > > + /* Must be called with args as a NULL pointer
> > > + * we do not check for it to have the verifier consider that
> > > + * the pointer might not be null, and so we can load it.
> > > + *
> > > + * So the following can not be added:
> > > + *
> > > + * if (args)
> > > + * return -22;
> > > + */
> > > +
> > > + bpf_kfunc_call_test_mem_len_pass1(args, sizeof(*args));
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +char _license[] SEC("license") = "GPL";
> > > diff --git a/tools/testing/selftests/bpf/progs/kfunc_call_test.c b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > > index 5aecbb9fdc68..94c05267e5e7 100644
> > > --- a/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > > +++ b/tools/testing/selftests/bpf/progs/kfunc_call_test.c
> > > @@ -92,4 +92,42 @@ int kfunc_call_test_pass(struct __sk_buff *skb)
> > > return 0;
> > > }
> > >
> > > +struct syscall_test_args {
> > > + __u8 data[16];
> > > + size_t size;
> > > +};
> > > +
> > > +SEC("syscall")
> > > +int kfunc_syscall_test(struct syscall_test_args *args)
> > > +{
> > > + const int size = args->size;
> > > +
> > > + if (size > sizeof(args->data))
> > > + return -7; /* -E2BIG */
> > > +
> >
> > Looks like it is due to this. Verifier is confused because:
> > r7 = args->data;
> > r1 = r7;
> >
> > then it does r1 <<= 32; r1 >>=32; clearing upper 32 bits, so both r1
> > and r7 lose the id association which propagates the bounds of r1
> > learnt from comparison of it with sizeof(args->data);
> >
> > > + bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(args->data));
> > > + bpf_kfunc_call_test_mem_len_pass1(&args->data, sizeof(*args));
> >
> > Later llvm assigns r7 to r2 for this call's 2nd arg. At this point the
> > verifier still thinks r7 is unbounded, while to make a call with mem,
> > len pair you need non-negative min value.
> >
> > Easiest way might be to just do args->size & sizeof(args->data), as
> > the verifier log says. You might still keep the error above.
> > Others may have better ideas/insights.
>
> I just did s/const int size/const long size/
> to fix the issues.
>
> Also fixed commit in patch 3 that talks about max_ctx_offset
> and did:
> - BTF_KFUNC_SET_MAX_CNT = 64,
> + BTF_KFUNC_SET_MAX_CNT = 256,
>
> and applied.
>
Great!
Many thanks to both of you for your time and getting me there :)
Cheers,
Benjamin
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