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Date: Thu, 4 Nov 2021 17:17:54 +0000
From: Song Liu <songliubraving@...com>
To: Yonghong Song <yhs@...com>
CC: bpf <bpf@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"ast@...nel.org" <ast@...nel.org>,
"daniel@...earbox.net" <daniel@...earbox.net>,
"andrii@...nel.org" <andrii@...nel.org>,
Kernel Team <Kernel-team@...com>,
"kpsingh@...nel.org" <kpsingh@...nel.org>
Subject: Re: [PATCH v2 bpf-next 2/2] selftests/bpf: add tests for bpf_find_vma
> On Nov 4, 2021, at 10:07 AM, Yonghong Song <yhs@...com> wrote:
>
>
>
> On 11/4/21 12:00 AM, Song Liu wrote:
>> Add tests for bpf_find_vma in perf_event program and kprobe program. The
>> perf_event program is triggered from NMI context, so the second call of
>> bpf_find_vma() will return -EBUSY (irq_work busy). The kprobe program,
>> on the other hand, does not have this constraint.
>> Also add test for illegal writes to task or vma from the callback
>> function. The verifier should reject both cases.
>> Signed-off-by: Song Liu <songliubraving@...com>
[...]
>> +static void test_find_vma_pe(struct find_vma *skel)
>> +{
>> + struct bpf_link *link = NULL;
>> + volatile int j = 0;
>> + int pfd = -1, i;
>> +
>> + pfd = open_pe();
>> + if (pfd < 0) {
>> + if (pfd == -ENOENT || pfd == -EOPNOTSUPP) {
>> + printf("%s:SKIP:no PERF_COUNT_HW_CPU_CYCLES\n", __func__);
>> + test__skip();
>> + }
>> + if (!ASSERT_GE(pfd, 0, "perf_event_open"))
>> + goto cleanup;
>> + }
>> +
>> + link = bpf_program__attach_perf_event(skel->progs.handle_pe, pfd);
>> + if (!ASSERT_OK_PTR(link, "attach_perf_event"))
>> + goto cleanup;
>> +
>> + for (i = 0; i < 1000000; ++i)
>> + ++j;
>
> Does this really work? Compiler could do
> j += 1000000;
I think compiler won't do it with volatile j?
>
>> +
>> + test_and_reset_skel(skel, -EBUSY /* in nmi, irq_work is busy */);
>> +cleanup:
>> + bpf_link__destroy(link);
>> + close(pfd);
>> + /* caller will clean up skel */
>
> Above comment is not needed. It should be clear from the code.
>
>> +}
>> +
>> +static void test_find_vma_kprobe(struct find_vma *skel)
>> +{
>> + int err;
>> +
>> + err = find_vma__attach(skel);
>> + if (!ASSERT_OK(err, "get_branch_snapshot__attach"))
>> + return; /* caller will cleanup skel */
>> +
>> + getpgid(skel->bss->target_pid);
>> + test_and_reset_skel(skel, -ENOENT /* could not find vma for ptr 0 */);
>> +}
>> +
>> +static void test_illegal_write_vma(void)
>> +{
>> + struct find_vma_fail1 *skel;
>> +
>> + skel = find_vma_fail1__open_and_load();
>> + ASSERT_ERR_PTR(skel, "find_vma_fail1__open_and_load");
>> +}
>> +
>> +static void test_illegal_write_task(void)
>> +{
>> + struct find_vma_fail2 *skel;
>> +
>> + skel = find_vma_fail2__open_and_load();
>> + ASSERT_ERR_PTR(skel, "find_vma_fail2__open_and_load");
>> +}
>> +
>> +void serial_test_find_vma(void)
>> +{
>> + struct find_vma *skel;
>> +
>> + skel = find_vma__open_and_load();
>> + if (!ASSERT_OK_PTR(skel, "find_vma__open_and_load"))
>> + return;
>> +
>> + skel->bss->target_pid = getpid();
>> + skel->bss->addr = (__u64)test_find_vma_pe;
>> +
>> + test_find_vma_pe(skel);
>> + usleep(100000); /* allow the irq_work to finish */
>> + test_find_vma_kprobe(skel);
>> +
>> + find_vma__destroy(skel);
>> + test_illegal_write_vma();
>> + test_illegal_write_task();
>> +}
>> diff --git a/tools/testing/selftests/bpf/progs/find_vma.c b/tools/testing/selftests/bpf/progs/find_vma.c
>> new file mode 100644
>> index 0000000000000..2776718a54e29
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/find_vma.c
>> @@ -0,0 +1,70 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2021 Facebook */
>> +#include "vmlinux.h"
>> +#include <bpf/bpf_helpers.h>
>> +#include <bpf/bpf_tracing.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +struct callback_ctx {
>> + int dummy;
>> +};
>> +
>> +#define VM_EXEC 0x00000004
>> +#define DNAME_INLINE_LEN 32
>> +
>> +pid_t target_pid = 0;
>> +char d_iname[DNAME_INLINE_LEN] = {0};
>> +__u32 found_vm_exec = 0;
>> +__u64 addr = 0;
>> +int find_zero_ret = -1;
>> +int find_addr_ret = -1;
>> +
>> +static __u64
>
> Let us 'long' instead of '__u64' to match uapi bpf.h.
>
>> +check_vma(struct task_struct *task, struct vm_area_struct *vma,
>> + struct callback_ctx *data)
>> +{
>> + if (vma->vm_file)
>> + bpf_probe_read_kernel_str(d_iname, DNAME_INLINE_LEN - 1,
>> + vma->vm_file->f_path.dentry->d_iname);
>> +
>> + /* check for VM_EXEC */
>> + if (vma->vm_flags & VM_EXEC)
>> + found_vm_exec = 1;
>> +
>> + return 0;
>> +}
>> +
>> +SEC("kprobe/__x64_sys_getpgid")
>
> The test will fail for non x86_64 architecture.
> I had some tweaks in test_probe_user.c. Please take a look.
> We can refactor to make tweaks in test_probe_user.c reusable
> by other files.
Good point. I will look into this.
>
>> +int handle_getpid(void)
>> +{
>> + struct task_struct *task = bpf_get_current_task_btf();
>> + struct callback_ctx data = {0};
>> +
>> + if (task->pid != target_pid)
>> + return 0;
>> +
>> + find_addr_ret = bpf_find_vma(task, addr, check_vma, &data, 0);
>> +
>> + /* this should return -ENOENT */
>> + find_zero_ret = bpf_find_vma(task, 0, check_vma, &data, 0);
>> + return 0;
>> +}
>> +
>> +SEC("perf_event")
>> +int handle_pe(void)
>> +{
>> + struct task_struct *task = bpf_get_current_task_btf();
>> + struct callback_ctx data = {0};
>> +
>> + if (task->pid != target_pid)
>> + return 0;
>
> This is tricky. How do we guarantee task->pid == target_pid hit?
> This probably mostly okay in serial running mode. But it may
> become more challenging if test_progs is running in parallel mode?
This is on a per task perf_event, so it shouldn't hit other tasks.
>
>> +
>> + find_addr_ret = bpf_find_vma(task, addr, check_vma, &data, 0);
>> +
>> + /* In NMI, this should return -EBUSY, as the previous call is using
>> + * the irq_work.
>> + */
>> + find_zero_ret = bpf_find_vma(task, 0, check_vma, &data, 0);
>> + return 0;
>> +}
>> diff --git a/tools/testing/selftests/bpf/progs/find_vma_fail1.c b/tools/testing/selftests/bpf/progs/find_vma_fail1.c
>> new file mode 100644
>> index 0000000000000..d17bdcdf76f07
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/find_vma_fail1.c
>> @@ -0,0 +1,30 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2021 Facebook */
>> +#include "vmlinux.h"
>> +#include <bpf/bpf_helpers.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +struct callback_ctx {
>> + int dummy;
>> +};
>> +
>> +static __u64
>
> __u64 => long
>
>> +write_vma(struct task_struct *task, struct vm_area_struct *vma,
>> + struct callback_ctx *data)
>> +{
>> + /* writing to vma, which is illegal */
>> + vma->vm_flags |= 0x55;
>> +
>> + return 0;
>> +}
>> +
>> +SEC("kprobe/__x64_sys_getpgid")
>> +int handle_getpid(void)
>> +{
>> + struct task_struct *task = bpf_get_current_task_btf();
>> + struct callback_ctx data = {0};
>> +
>> + bpf_find_vma(task, 0, write_vma, &data, 0);
>> + return 0;
>> +}
>> diff --git a/tools/testing/selftests/bpf/progs/find_vma_fail2.c b/tools/testing/selftests/bpf/progs/find_vma_fail2.c
>> new file mode 100644
>> index 0000000000000..079c4594c095d
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/find_vma_fail2.c
>> @@ -0,0 +1,30 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +/* Copyright (c) 2021 Facebook */
>> +#include "vmlinux.h"
>> +#include <bpf/bpf_helpers.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +struct callback_ctx {
>> + int dummy;
>> +};
>> +
>> +static __u64
>
> __u64 => long
>
>> +write_task(struct task_struct *task, struct vm_area_struct *vma,
>> + struct callback_ctx *data)
>> +{
>> + /* writing to task, which is illegal */
>> + task->mm = NULL;
>> +
>> + return 0;
>> +}
>> +
>> +SEC("kprobe/__x64_sys_getpgid")
>> +int handle_getpid(void)
>> +{
>> + struct task_struct *task = bpf_get_current_task_btf();
>> + struct callback_ctx data = {0};
>> +
>> + bpf_find_vma(task, 0, write_task, &data, 0);
>> + return 0;
>> +}
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