Re: [PATCH bpf-next v11 4/7] selftests/bpf: add test for accessing ctx from syscall program type

From: Kumar Kartikeya Dwivedi
Date: Wed Sep 07 2022 - 13:46:14 EST

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In reply to: Benjamin Tissoires: "[PATCH bpf-next v11 4/7] selftests/bpf: add test for accessing ctx from syscall program type"
Next in thread: Alexei Starovoitov: "Re: [PATCH bpf-next v11 4/7] selftests/bpf: add test for accessing ctx from syscall program type"
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On Tue, 6 Sept 2022 at 17:13, Benjamin Tissoires
<benjamin.tissoires@xxxxxxxxxx> 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@xxxxxxxxxx>
>
> ---

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.

> + bpf_kfunc_call_test_mem_len_pass1(&args->data, size);
> +
> + return 0;
> +}
> +
> +SEC("syscall")
> +int kfunc_syscall_test_null(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, 0);
> +
> + return 0;
> +}
> +
> char _license[] SEC("license") = "GPL";
> --
> 2.36.1
>

Next message: Marco Elver: "Re: [PATCH 2/2] objtool, kcsan: Add volatile read/write instrumentation to whitelist"
Previous message: Alper Gun: "Re: [PATCH Part2 v6 31/49] KVM: x86: Introduce kvm_mmu_get_tdp_walk() for SEV-SNP use"
In reply to: Benjamin Tissoires: "[PATCH bpf-next v11 4/7] selftests/bpf: add test for accessing ctx from syscall program type"
Next in thread: Alexei Starovoitov: "Re: [PATCH bpf-next v11 4/7] selftests/bpf: add test for accessing ctx from syscall program type"
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