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Merge branch 'fix-bpf_get_stack-with-PEBS'

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Song Liu says:

====================
Calling get_perf_callchain() on perf_events from PEBS entries may cause
unwinder errors. To fix this issue, perf subsystem fetches callchain early,
and marks perf_events are marked with __PERF_SAMPLE_CALLCHAIN_EARLY.
Similar issue exists when BPF program calls get_perf_callchain() via
helper functions. For more information about this issue, please refer to
discussions in [1].

This set fixes this issue with helper proto bpf_get_stackid_pe and
bpf_get_stack_pe.

[1] https://lore.kernel.org/lkml/ED7B9430-6489-4260-B3C5-9CFA2E3AA87A@fb.com/

Changes v4 => v5:
1. Return -EPROTO instead of -EINVAL on PERF_EVENT_IOC_SET_BPF errors.
   (Alexei)
2. Let libbpf print a hint message when PERF_EVENT_IOC_SET_BPF returns
   -EPROTO. (Alexei)

Changes v3 => v4:
1. Fix error check logic in bpf_get_stackid_pe and bpf_get_stack_pe.
   (Alexei)
2. Do not allow attaching BPF programs with bpf_get_stack|stackid to
   perf_event with precise_ip > 0, but not proper callchain. (Alexei)
3. Add selftest get_stackid_cannot_attach.

Changes v2 => v3:
1. Fix handling of stackmap skip field. (Andrii)
2. Simplify the code in a few places. (Andrii)

Changes v1 => v2:
1. Simplify the design and avoid introducing new helper function. (Andrii)
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Alexei Starovoitov 2020-07-23 22:20:32 -07:00
commit 90065c0647
10 changed files with 462 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
include/linux/bpf.h
View File

@ -1675,6 +1675,8 @@ extern const struct bpf_func_proto bpf_get_current_comm_proto;
extern const struct bpf_func_proto bpf_get_stackid_proto;
extern const struct bpf_func_proto bpf_get_stack_proto;
extern const struct bpf_func_proto bpf_get_task_stack_proto;
extern const struct bpf_func_proto bpf_get_stackid_proto_pe;
extern const struct bpf_func_proto bpf_get_stack_proto_pe;
extern const struct bpf_func_proto bpf_sock_map_update_proto;
extern const struct bpf_func_proto bpf_sock_hash_update_proto;
extern const struct bpf_func_proto bpf_get_current_cgroup_id_proto;

3
include/linux/filter.h
View File

@ -533,7 +533,8 @@ struct bpf_prog {
is_func:1, /* program is a bpf function */
kprobe_override:1, /* Do we override a kprobe? */
has_callchain_buf:1, /* callchain buffer allocated? */
enforce_expected_attach_type:1; /* Enforce expected_attach_type checking at attach time */
enforce_expected_attach_type:1, /* Enforce expected_attach_type checking at attach time */
call_get_stack:1; /* Do we call bpf_get_stack() or bpf_get_stackid() */
enum bpf_prog_type type; /* Type of BPF program */
enum bpf_attach_type expected_attach_type; /* For some prog types */
u32 len; /* Number of filter blocks */

184
kernel/bpf/stackmap.c
View File

@ -4,6 +4,7 @@
#include <linux/bpf.h>
#include <linux/jhash.h>
#include <linux/filter.h>
#include <linux/kernel.h>
#include <linux/stacktrace.h>
#include <linux/perf_event.h>
#include <linux/elf.h>
@ -387,11 +388,10 @@ get_callchain_entry_for_task(struct task_struct *task, u32 init_nr)
#endif
}
BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
u64, flags)
static long __bpf_get_stackid(struct bpf_map *map,
struct perf_callchain_entry *trace, u64 flags)
{
struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
struct perf_callchain_entry *trace;
struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
u32 max_depth = map->value_size / stack_map_data_size(map);
/* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */
@ -399,21 +399,9 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
u32 hash, id, trace_nr, trace_len;
bool user = flags & BPF_F_USER_STACK;
bool kernel = !user;
u64 *ips;
bool hash_matches;
if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
return -EINVAL;
trace = get_perf_callchain(regs, init_nr, kernel, user,
sysctl_perf_event_max_stack, false, false);
if (unlikely(!trace))
/* couldn't fetch the stack trace */
return -EFAULT;
/* get_perf_callchain() guarantees that trace->nr >= init_nr
* and trace-nr <= sysctl_perf_event_max_stack, so trace_nr <= max_depth
*/
@ -478,6 +466,30 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
return id;
}
BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
u64, flags)
{
u32 max_depth = map->value_size / stack_map_data_size(map);
/* stack_map_alloc() checks that max_depth <= sysctl_perf_event_max_stack */
u32 init_nr = sysctl_perf_event_max_stack - max_depth;
bool user = flags & BPF_F_USER_STACK;
struct perf_callchain_entry *trace;
bool kernel = !user;
if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
return -EINVAL;
trace = get_perf_callchain(regs, init_nr, kernel, user,
sysctl_perf_event_max_stack, false, false);
if (unlikely(!trace))
/* couldn't fetch the stack trace */
return -EFAULT;
return __bpf_get_stackid(map, trace, flags);
}
const struct bpf_func_proto bpf_get_stackid_proto = {
.func = bpf_get_stackid,
.gpl_only = true,
@ -487,7 +499,77 @@ const struct bpf_func_proto bpf_get_stackid_proto = {
.arg3_type = ARG_ANYTHING,
};
static __u64 count_kernel_ip(struct perf_callchain_entry *trace)
{
__u64 nr_kernel = 0;
while (nr_kernel < trace->nr) {
if (trace->ip[nr_kernel] == PERF_CONTEXT_USER)
break;
nr_kernel++;
}
return nr_kernel;
}
BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
struct bpf_map *, map, u64, flags)
{
struct perf_event *event = ctx->event;
struct perf_callchain_entry *trace;
bool kernel, user;
__u64 nr_kernel;
int ret;
/* perf_sample_data doesn't have callchain, use bpf_get_stackid */
if (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY))
return bpf_get_stackid((unsigned long)(ctx->regs),
(unsigned long) map, flags, 0, 0);
if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID)))
return -EINVAL;
user = flags & BPF_F_USER_STACK;
kernel = !user;
trace = ctx->data->callchain;
if (unlikely(!trace))
return -EFAULT;
nr_kernel = count_kernel_ip(trace);
if (kernel) {
__u64 nr = trace->nr;
trace->nr = nr_kernel;
ret = __bpf_get_stackid(map, trace, flags);
/* restore nr */
trace->nr = nr;
} else { /* user */
u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
skip += nr_kernel;
if (skip > BPF_F_SKIP_FIELD_MASK)
return -EFAULT;
flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
ret = __bpf_get_stackid(map, trace, flags);
}
return ret;
}
const struct bpf_func_proto bpf_get_stackid_proto_pe = {
.func = bpf_get_stackid_pe,
.gpl_only = false,
.ret_type = RET_INTEGER,
.arg1_type = ARG_PTR_TO_CTX,
.arg2_type = ARG_CONST_MAP_PTR,
.arg3_type = ARG_ANYTHING,
};
static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
struct perf_callchain_entry *trace_in,
void *buf, u32 size, u64 flags)
{
u32 init_nr, trace_nr, copy_len, elem_size, num_elem;
@ -520,7 +602,9 @@ static long __bpf_get_stack(struct pt_regs *regs, struct task_struct *task,
else
init_nr = sysctl_perf_event_max_stack - num_elem;
if (kernel && task)
if (trace_in)
trace = trace_in;
else if (kernel && task)
trace = get_callchain_entry_for_task(task, init_nr);
else
trace = get_perf_callchain(regs, init_nr, kernel, user,
@ -556,7 +640,7 @@ clear:
BPF_CALL_4(bpf_get_stack, struct pt_regs *, regs, void *, buf, u32, size,
u64, flags)
{
return __bpf_get_stack(regs, NULL, buf, size, flags);
return __bpf_get_stack(regs, NULL, NULL, buf, size, flags);
}
const struct bpf_func_proto bpf_get_stack_proto = {
@ -574,7 +658,7 @@ BPF_CALL_4(bpf_get_task_stack, struct task_struct *, task, void *, buf,
{
struct pt_regs *regs = task_pt_regs(task);
return __bpf_get_stack(regs, task, buf, size, flags);
return __bpf_get_stack(regs, task, NULL, buf, size, flags);
}
BTF_ID_LIST(bpf_get_task_stack_btf_ids)
@ -591,6 +675,70 @@ const struct bpf_func_proto bpf_get_task_stack_proto = {
.btf_id = bpf_get_task_stack_btf_ids,
};
BPF_CALL_4(bpf_get_stack_pe, struct bpf_perf_event_data_kern *, ctx,
void *, buf, u32, size, u64, flags)
{
struct perf_event *event = ctx->event;
struct perf_callchain_entry *trace;
bool kernel, user;
int err = -EINVAL;
__u64 nr_kernel;
if (!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY))
return __bpf_get_stack(ctx->regs, NULL, NULL, buf, size, flags);
if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK |
BPF_F_USER_BUILD_ID)))
goto clear;
user = flags & BPF_F_USER_STACK;
kernel = !user;
err = -EFAULT;
trace = ctx->data->callchain;
if (unlikely(!trace))
goto clear;
nr_kernel = count_kernel_ip(trace);
if (kernel) {
__u64 nr = trace->nr;
trace->nr = nr_kernel;
err = __bpf_get_stack(ctx->regs, NULL, trace, buf,
size, flags);
/* restore nr */
trace->nr = nr;
} else { /* user */
u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
skip += nr_kernel;
if (skip > BPF_F_SKIP_FIELD_MASK)
goto clear;
flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
err = __bpf_get_stack(ctx->regs, NULL, trace, buf,
size, flags);
}
return err;
clear:
memset(buf, 0, size);
return err;
}
const struct bpf_func_proto bpf_get_stack_proto_pe = {
.func = bpf_get_stack_pe,
.gpl_only = true,
.ret_type = RET_INTEGER,
.arg1_type = ARG_PTR_TO_CTX,
.arg2_type = ARG_PTR_TO_UNINIT_MEM,
.arg3_type = ARG_CONST_SIZE_OR_ZERO,
.arg4_type = ARG_ANYTHING,
};
/* Called from eBPF program */
static void *stack_map_lookup_elem(struct bpf_map *map, void *key)
{

3
kernel/bpf/verifier.c
View File

@ -4962,6 +4962,9 @@ static int check_helper_call(struct bpf_verifier_env *env, int func_id, int insn
env->prog->has_callchain_buf = true;
}
if (func_id == BPF_FUNC_get_stackid || func_id == BPF_FUNC_get_stack)
env->prog->call_get_stack = true;
if (changes_data)
clear_all_pkt_pointers(env);
return 0;

18
kernel/events/core.c
View File

@ -9544,6 +9544,24 @@ static int perf_event_set_bpf_handler(struct perf_event *event, u32 prog_fd)
if (IS_ERR(prog))
return PTR_ERR(prog);
if (event->attr.precise_ip &&
prog->call_get_stack &&
(!(event->attr.sample_type & __PERF_SAMPLE_CALLCHAIN_EARLY) ||
event->attr.exclude_callchain_kernel ||
event->attr.exclude_callchain_user)) {
/*
* On perf_event with precise_ip, calling bpf_get_stack()
* may trigger unwinder warnings and occasional crashes.
* bpf_get_[stack|stackid] works around this issue by using
* callchain attached to perf_sample_data. If the
* perf_event does not full (kernel and user) callchain
* attached to perf_sample_data, do not allow attaching BPF
* program that calls bpf_get_[stack|stackid].
*/
bpf_prog_put(prog);
return -EPROTO;
}
event->prog = prog;
event->orig_overflow_handler = READ_ONCE(event->overflow_handler);
WRITE_ONCE(event->overflow_handler, bpf_overflow_handler);

4
kernel/trace/bpf_trace.c
View File

@ -1411,9 +1411,9 @@ pe_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
case BPF_FUNC_perf_event_output:
return &bpf_perf_event_output_proto_tp;
case BPF_FUNC_get_stackid:
return &bpf_get_stackid_proto_tp;
return &bpf_get_stackid_proto_pe;
case BPF_FUNC_get_stack:
return &bpf_get_stack_proto_tp;
return &bpf_get_stack_proto_pe;
case BPF_FUNC_perf_prog_read_value:
return &bpf_perf_prog_read_value_proto;
case BPF_FUNC_read_branch_records:

3
tools/lib/bpf/libbpf.c
View File

@ -7833,6 +7833,9 @@ struct bpf_link *bpf_program__attach_perf_event(struct bpf_program *prog,
pr_warn("program '%s': failed to attach to pfd %d: %s\n",
bpf_program__title(prog, false), pfd,
libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
if (err == -EPROTO)
pr_warn("program '%s': try add PERF_SAMPLE_CALLCHAIN to or remove exclude_callchain_[kernel|user] from pfd %d\n",
bpf_program__title(prog, false), pfd);
return ERR_PTR(err);
}
if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {

91
tools/testing/selftests/bpf/prog_tests/get_stackid_cannot_attach.c Normal file
View File

@ -0,0 +1,91 @@
// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2020 Facebook
#include <test_progs.h>
#include "test_stacktrace_build_id.skel.h"
void test_get_stackid_cannot_attach(void)
{
struct perf_event_attr attr = {
/* .type = PERF_TYPE_SOFTWARE, */
.type = PERF_TYPE_HARDWARE,
.config = PERF_COUNT_HW_CPU_CYCLES,
.precise_ip = 1,
.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_BRANCH_STACK,
.branch_sample_type = PERF_SAMPLE_BRANCH_USER |
PERF_SAMPLE_BRANCH_NO_FLAGS |
PERF_SAMPLE_BRANCH_NO_CYCLES |
PERF_SAMPLE_BRANCH_CALL_STACK,
.sample_period = 5000,
.size = sizeof(struct perf_event_attr),
};
struct test_stacktrace_build_id *skel;
__u32 duration = 0;
int pmu_fd, err;
skel = test_stacktrace_build_id__open();
if (CHECK(!skel, "skel_open", "skeleton open failed\n"))
return;
/* override program type */
bpf_program__set_perf_event(skel->progs.oncpu);
err = test_stacktrace_build_id__load(skel);
if (CHECK(err, "skel_load", "skeleton load failed: %d\n", err))
goto cleanup;
pmu_fd = syscall(__NR_perf_event_open, &attr, -1 /* pid */,
0 /* cpu 0 */, -1 /* group id */,
0 /* flags */);
if (pmu_fd < 0 && (errno == ENOENT || errno == EOPNOTSUPP)) {
printf("%s:SKIP:cannot open PERF_COUNT_HW_CPU_CYCLES with precise_ip > 0\n",
__func__);
test__skip();
goto cleanup;
}
if (CHECK(pmu_fd < 0, "perf_event_open", "err %d errno %d\n",
pmu_fd, errno))
goto cleanup;
skel->links.oncpu = bpf_program__attach_perf_event(skel->progs.oncpu,
pmu_fd);
CHECK(!IS_ERR(skel->links.oncpu), "attach_perf_event_no_callchain",
"should have failed\n");
close(pmu_fd);
/* add PERF_SAMPLE_CALLCHAIN, attach should succeed */
attr.sample_type |= PERF_SAMPLE_CALLCHAIN;
pmu_fd = syscall(__NR_perf_event_open, &attr, -1 /* pid */,
0 /* cpu 0 */, -1 /* group id */,
0 /* flags */);
if (CHECK(pmu_fd < 0, "perf_event_open", "err %d errno %d\n",
pmu_fd, errno))
goto cleanup;
skel->links.oncpu = bpf_program__attach_perf_event(skel->progs.oncpu,
pmu_fd);
CHECK(IS_ERR(skel->links.oncpu), "attach_perf_event_callchain",
"err: %ld\n", PTR_ERR(skel->links.oncpu));
close(pmu_fd);
/* add exclude_callchain_kernel, attach should fail */
attr.exclude_callchain_kernel = 1;
pmu_fd = syscall(__NR_perf_event_open, &attr, -1 /* pid */,
0 /* cpu 0 */, -1 /* group id */,
0 /* flags */);
if (CHECK(pmu_fd < 0, "perf_event_open", "err %d errno %d\n",
pmu_fd, errno))
goto cleanup;
skel->links.oncpu = bpf_program__attach_perf_event(skel->progs.oncpu,
pmu_fd);
CHECK(!IS_ERR(skel->links.oncpu), "attach_perf_event_exclude_callchain_kernel",
"should have failed\n");
close(pmu_fd);
cleanup:
test_stacktrace_build_id__destroy(skel);
}

116
tools/testing/selftests/bpf/prog_tests/perf_event_stackmap.c Normal file
View File

@ -0,0 +1,116 @@
// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2020 Facebook
#define _GNU_SOURCE
#include <pthread.h>
#include <sched.h>
#include <test_progs.h>
#include "perf_event_stackmap.skel.h"
#ifndef noinline
#define noinline __attribute__((noinline))
#endif
noinline int func_1(void)
{
static int val = 1;
val += 1;
usleep(100);
return val;
}
noinline int func_2(void)
{
return func_1();
}
noinline int func_3(void)
{
return func_2();
}
noinline int func_4(void)
{
return func_3();
}
noinline int func_5(void)
{
return func_4();
}
noinline int func_6(void)
{
int i, val = 1;
for (i = 0; i < 100; i++)
val += func_5();
return val;
}
void test_perf_event_stackmap(void)
{
struct perf_event_attr attr = {
/* .type = PERF_TYPE_SOFTWARE, */
.type = PERF_TYPE_HARDWARE,
.config = PERF_COUNT_HW_CPU_CYCLES,
.precise_ip = 2,
.sample_type = PERF_SAMPLE_IP | PERF_SAMPLE_BRANCH_STACK |
PERF_SAMPLE_CALLCHAIN,
.branch_sample_type = PERF_SAMPLE_BRANCH_USER |
PERF_SAMPLE_BRANCH_NO_FLAGS |
PERF_SAMPLE_BRANCH_NO_CYCLES |
PERF_SAMPLE_BRANCH_CALL_STACK,
.sample_period = 5000,
.size = sizeof(struct perf_event_attr),
};
struct perf_event_stackmap *skel;
__u32 duration = 0;
cpu_set_t cpu_set;
int pmu_fd, err;
skel = perf_event_stackmap__open();
if (CHECK(!skel, "skel_open", "skeleton open failed\n"))
return;
err = perf_event_stackmap__load(skel);
if (CHECK(err, "skel_load", "skeleton load failed: %d\n", err))
goto cleanup;
CPU_ZERO(&cpu_set);
CPU_SET(0, &cpu_set);
err = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set), &cpu_set);
if (CHECK(err, "set_affinity", "err %d, errno %d\n", err, errno))
goto cleanup;
pmu_fd = syscall(__NR_perf_event_open, &attr, -1 /* pid */,
0 /* cpu 0 */, -1 /* group id */,
0 /* flags */);
if (pmu_fd < 0) {
printf("%s:SKIP:cpu doesn't support the event\n", __func__);
test__skip();
goto cleanup;
}
skel->links.oncpu = bpf_program__attach_perf_event(skel->progs.oncpu,
pmu_fd);
if (CHECK(IS_ERR(skel->links.oncpu), "attach_perf_event",
"err %ld\n", PTR_ERR(skel->links.oncpu))) {
close(pmu_fd);
goto cleanup;
}
/* create kernel and user stack traces for testing */
func_6();
CHECK(skel->data->stackid_kernel != 2, "get_stackid_kernel", "failed\n");
CHECK(skel->data->stackid_user != 2, "get_stackid_user", "failed\n");
CHECK(skel->data->stack_kernel != 2, "get_stack_kernel", "failed\n");
CHECK(skel->data->stack_user != 2, "get_stack_user", "failed\n");
cleanup:
perf_event_stackmap__destroy(skel);
}

59
tools/testing/selftests/bpf/progs/perf_event_stackmap.c Normal file
View File

@ -0,0 +1,59 @@
// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2020 Facebook
#include "vmlinux.h"
#include <bpf/bpf_helpers.h>
#ifndef PERF_MAX_STACK_DEPTH
#define PERF_MAX_STACK_DEPTH 127
#endif
typedef __u64 stack_trace_t[PERF_MAX_STACK_DEPTH];
struct {
__uint(type, BPF_MAP_TYPE_STACK_TRACE);
__uint(max_entries, 16384);
__uint(key_size, sizeof(__u32));
__uint(value_size, sizeof(stack_trace_t));
} stackmap SEC(".maps");
struct {
__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
__uint(max_entries, 1);
__type(key, __u32);
__type(value, stack_trace_t);
} stackdata_map SEC(".maps");
long stackid_kernel = 1;
long stackid_user = 1;
long stack_kernel = 1;
long stack_user = 1;
SEC("perf_event")
int oncpu(void *ctx)
{
stack_trace_t *trace;
__u32 key = 0;
long val;
val = bpf_get_stackid(ctx, &stackmap, 0);
if (val > 0)
stackid_kernel = 2;
val = bpf_get_stackid(ctx, &stackmap, BPF_F_USER_STACK);
if (val > 0)
stackid_user = 2;
trace = bpf_map_lookup_elem(&stackdata_map, &key);
if (!trace)
return 0;
val = bpf_get_stack(ctx, trace, sizeof(stack_trace_t), 0);
if (val > 0)
stack_kernel = 2;
val = bpf_get_stack(ctx, trace, sizeof(stack_trace_t), BPF_F_USER_STACK);
if (val > 0)
stack_user = 2;
return 0;
}
char LICENSE[] SEC("license") = "GPL";