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bpf: Introduce helper bpf_find_vma 

In some profiler use cases, it is necessary to map an address to the
backing file, e.g., a shared library. bpf_find_vma helper provides a
flexible way to achieve this. bpf_find_vma maps an address of a task to
the vma (vm_area_struct) for this address, and feed the vma to an callback
BPF function. The callback function is necessary here, as we need to
ensure mmap_sem is unlocked.

It is necessary to lock mmap_sem for find_vma. To lock and unlock mmap_sem
safely when irqs are disable, we use the same mechanism as stackmap with
build_id. Specifically, when irqs are disabled, the unlocked is postponed
in an irq_work. Refactor stackmap.c so that the irq_work is shared among
bpf_find_vma and stackmap helpers.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Hengqi Chen <hengqi.chen@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20211105232330.1936330-2-songliubraving@fb.com
This commit is contained in:
Song Liu 2021-11-05 16:23:29 -07:00 committed by Alexei Starovoitov
parent 5fd79ed9be
commit 7c7e3d31e7
9 changed files with 222 additions and 81 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
include/linux/bpf.h
View File

@ -2157,6 +2157,7 @@ extern const struct bpf_func_proto bpf_btf_find_by_name_kind_proto;
extern const struct bpf_func_proto bpf_sk_setsockopt_proto;
extern const struct bpf_func_proto bpf_sk_getsockopt_proto;
extern const struct bpf_func_proto bpf_kallsyms_lookup_name_proto;
extern const struct bpf_func_proto bpf_find_vma_proto;
const struct bpf_func_proto *tracing_prog_func_proto(
enum bpf_func_id func_id, const struct bpf_prog *prog);

20
include/uapi/linux/bpf.h
View File

@ -4938,6 +4938,25 @@ union bpf_attr {
* **-ENOENT** if symbol is not found.
*
* **-EPERM** if caller does not have permission to obtain kernel address.
*
* long bpf_find_vma(struct task_struct *task, u64 addr, void *callback_fn, void *callback_ctx, u64 flags)
* Description
* Find vma of *task* that contains *addr*, call *callback_fn*
* function with *task*, *vma*, and *callback_ctx*.
* The *callback_fn* should be a static function and
* the *callback_ctx* should be a pointer to the stack.
* The *flags* is used to control certain aspects of the helper.
* Currently, the *flags* must be 0.
*
* The expected callback signature is
*
* long (\*callback_fn)(struct task_struct \*task, struct vm_area_struct \*vma, void \*callback_ctx);
*
* Return
* 0 on success.
* **-ENOENT** if *task->mm* is NULL, or no vma contains *addr*.
* **-EBUSY** if failed to try lock mmap_lock.
* **-EINVAL** for invalid **flags**.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@ -5120,6 +5139,7 @@ union bpf_attr {
FN(trace_vprintk), \
FN(skc_to_unix_sock), \
FN(kallsyms_lookup_name), \
FN(find_vma), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper

5
kernel/bpf/btf.c
View File

@ -6342,7 +6342,10 @@ const struct bpf_func_proto bpf_btf_find_by_name_kind_proto = {
.arg4_type = ARG_ANYTHING,
};
BTF_ID_LIST_GLOBAL_SINGLE(btf_task_struct_ids, struct, task_struct)
BTF_ID_LIST_GLOBAL(btf_task_struct_ids)
BTF_ID(struct, task_struct)
BTF_ID(struct, file)
BTF_ID(struct, vm_area_struct)
/* BTF ID set registration API for modules */

65
kernel/bpf/mmap_unlock_work.h Normal file
View File

@ -0,0 +1,65 @@
/* SPDX-License-Identifier: GPL-2.0-only */
/* Copyright (c) 2021 Facebook
*/
#ifndef __MMAP_UNLOCK_WORK_H__
#define __MMAP_UNLOCK_WORK_H__
#include <linux/irq_work.h>
/* irq_work to run mmap_read_unlock() in irq_work */
struct mmap_unlock_irq_work {
struct irq_work irq_work;
struct mm_struct *mm;
};
DECLARE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
/*
* We cannot do mmap_read_unlock() when the irq is disabled, because of
* risk to deadlock with rq_lock. To look up vma when the irqs are
* disabled, we need to run mmap_read_unlock() in irq_work. We use a
* percpu variable to do the irq_work. If the irq_work is already used
* by another lookup, we fall over.
*/
static inline bool bpf_mmap_unlock_get_irq_work(struct mmap_unlock_irq_work **work_ptr)
{
struct mmap_unlock_irq_work *work = NULL;
bool irq_work_busy = false;
if (irqs_disabled()) {
if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
work = this_cpu_ptr(&mmap_unlock_work);
if (irq_work_is_busy(&work->irq_work)) {
/* cannot queue more up_read, fallback */
irq_work_busy = true;
}
} else {
/*
* PREEMPT_RT does not allow to trylock mmap sem in
* interrupt disabled context. Force the fallback code.
*/
irq_work_busy = true;
}
}
*work_ptr = work;
return irq_work_busy;
}
static inline void bpf_mmap_unlock_mm(struct mmap_unlock_irq_work *work, struct mm_struct *mm)
{
if (!work) {
mmap_read_unlock(mm);
} else {
work->mm = mm;
/* The lock will be released once we're out of interrupt
* context. Tell lockdep that we've released it now so
* it doesn't complain that we forgot to release it.
*/
rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_);
irq_work_queue(&work->irq_work);
}
}
#endif /* __MMAP_UNLOCK_WORK_H__ */

80
kernel/bpf/stackmap.c
View File

@ -7,10 +7,10 @@
#include <linux/kernel.h>
#include <linux/stacktrace.h>
#include <linux/perf_event.h>
#include <linux/irq_work.h>
#include <linux/btf_ids.h>
#include <linux/buildid.h>
#include "percpu_freelist.h"
#include "mmap_unlock_work.h"
#define STACK_CREATE_FLAG_MASK \
(BPF_F_NUMA_NODE | BPF_F_RDONLY | BPF_F_WRONLY | \
@ -31,25 +31,6 @@ struct bpf_stack_map {
struct stack_map_bucket *buckets[];
};
/* irq_work to run up_read() for build_id lookup in nmi context */
struct stack_map_irq_work {
struct irq_work irq_work;
struct mm_struct *mm;
};
static void do_up_read(struct irq_work *entry)
{
struct stack_map_irq_work *work;
if (WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)))
return;
work = container_of(entry, struct stack_map_irq_work, irq_work);
mmap_read_unlock_non_owner(work->mm);
}
static DEFINE_PER_CPU(struct stack_map_irq_work, up_read_work);
static inline bool stack_map_use_build_id(struct bpf_map *map)
{
return (map->map_flags & BPF_F_STACK_BUILD_ID);
@ -149,35 +130,13 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
u64 *ips, u32 trace_nr, bool user)
{
int i;
struct mmap_unlock_irq_work *work = NULL;
bool irq_work_busy = bpf_mmap_unlock_get_irq_work(&work);
struct vm_area_struct *vma;
bool irq_work_busy = false;
struct stack_map_irq_work *work = NULL;
if (irqs_disabled()) {
if (!IS_ENABLED(CONFIG_PREEMPT_RT)) {
work = this_cpu_ptr(&up_read_work);
if (irq_work_is_busy(&work->irq_work)) {
/* cannot queue more up_read, fallback */
irq_work_busy = true;
}
} else {
/*
* PREEMPT_RT does not allow to trylock mmap sem in
* interrupt disabled context. Force the fallback code.
*/
irq_work_busy = true;
}
}
/*
* We cannot do up_read() when the irq is disabled, because of
* risk to deadlock with rq_lock. To do build_id lookup when the
* irqs are disabled, we need to run up_read() in irq_work. We use
* a percpu variable to do the irq_work. If the irq_work is
* already used by another lookup, we fall back to report ips.
*
* Same fallback is used for kernel stack (!user) on a stackmap
* with build_id.
/* If the irq_work is in use, fall back to report ips. Same
* fallback is used for kernel stack (!user) on a stackmap with
* build_id.
*/
if (!user || !current || !current->mm || irq_work_busy ||
!mmap_read_trylock(current->mm)) {
@ -203,19 +162,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
- vma->vm_start;
id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
}
if (!work) {
mmap_read_unlock(current->mm);
} else {
work->mm = current->mm;
/* The lock will be released once we're out of interrupt
* context. Tell lockdep that we've released it now so
* it doesn't complain that we forgot to release it.
*/
rwsem_release(&current->mm->mmap_lock.dep_map, _RET_IP_);
irq_work_queue(&work->irq_work);
}
bpf_mmap_unlock_mm(work, current->mm);
}
static struct perf_callchain_entry *
@ -719,16 +666,3 @@ const struct bpf_map_ops stack_trace_map_ops = {
.map_btf_name = "bpf_stack_map",
.map_btf_id = &stack_trace_map_btf_id,
};
static int __init stack_map_init(void)
{
int cpu;
struct stack_map_irq_work *work;
for_each_possible_cpu(cpu) {
work = per_cpu_ptr(&up_read_work, cpu);
init_irq_work(&work->irq_work, do_up_read);
}
return 0;
}
subsys_initcall(stack_map_init);

76
kernel/bpf/task_iter.c
View File

@ -8,6 +8,7 @@
#include <linux/fdtable.h>
#include <linux/filter.h>
#include <linux/btf_ids.h>
#include "mmap_unlock_work.h"
struct bpf_iter_seq_task_common {
struct pid_namespace *ns;
@ -524,10 +525,6 @@ static const struct seq_operations task_vma_seq_ops = {
.show = task_vma_seq_show,
};
BTF_ID_LIST(btf_task_file_ids)
BTF_ID(struct, file)
BTF_ID(struct, vm_area_struct)
static const struct bpf_iter_seq_info task_seq_info = {
.seq_ops = &task_seq_ops,
.init_seq_private = init_seq_pidns,
@ -586,9 +583,74 @@ static struct bpf_iter_reg task_vma_reg_info = {
.seq_info = &task_vma_seq_info,
};
BPF_CALL_5(bpf_find_vma, struct task_struct *, task, u64, start,
bpf_callback_t, callback_fn, void *, callback_ctx, u64, flags)
{
struct mmap_unlock_irq_work *work = NULL;
struct vm_area_struct *vma;
bool irq_work_busy = false;
struct mm_struct *mm;
int ret = -ENOENT;
if (flags)
return -EINVAL;
if (!task)
return -ENOENT;
mm = task->mm;
if (!mm)
return -ENOENT;
irq_work_busy = bpf_mmap_unlock_get_irq_work(&work);
if (irq_work_busy || !mmap_read_trylock(mm))
return -EBUSY;
vma = find_vma(mm, start);
if (vma && vma->vm_start <= start && vma->vm_end > start) {
callback_fn((u64)(long)task, (u64)(long)vma,
(u64)(long)callback_ctx, 0, 0);
ret = 0;
}
bpf_mmap_unlock_mm(work, mm);
return ret;
}
const struct bpf_func_proto bpf_find_vma_proto = {
.func = bpf_find_vma,
.ret_type = RET_INTEGER,
.arg1_type = ARG_PTR_TO_BTF_ID,
.arg1_btf_id = &btf_task_struct_ids[0],
.arg2_type = ARG_ANYTHING,
.arg3_type = ARG_PTR_TO_FUNC,
.arg4_type = ARG_PTR_TO_STACK_OR_NULL,
.arg5_type = ARG_ANYTHING,
};
DEFINE_PER_CPU(struct mmap_unlock_irq_work, mmap_unlock_work);
static void do_mmap_read_unlock(struct irq_work *entry)
{
struct mmap_unlock_irq_work *work;
if (WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)))
return;
work = container_of(entry, struct mmap_unlock_irq_work, irq_work);
mmap_read_unlock_non_owner(work->mm);
}
static int __init task_iter_init(void)
{
int ret;
struct mmap_unlock_irq_work *work;
int ret, cpu;
for_each_possible_cpu(cpu) {
work = per_cpu_ptr(&mmap_unlock_work, cpu);
init_irq_work(&work->irq_work, do_mmap_read_unlock);
}
task_reg_info.ctx_arg_info[0].btf_id = btf_task_struct_ids[0];
ret = bpf_iter_reg_target(&task_reg_info);
@ -596,13 +658,13 @@ static int __init task_iter_init(void)
return ret;
task_file_reg_info.ctx_arg_info[0].btf_id = btf_task_struct_ids[0];
task_file_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[0];
task_file_reg_info.ctx_arg_info[1].btf_id = btf_task_struct_ids[1];
ret = bpf_iter_reg_target(&task_file_reg_info);
if (ret)
return ret;
task_vma_reg_info.ctx_arg_info[0].btf_id = btf_task_struct_ids[0];
task_vma_reg_info.ctx_arg_info[1].btf_id = btf_task_file_ids[1];
task_vma_reg_info.ctx_arg_info[1].btf_id = btf_task_struct_ids[2];
return bpf_iter_reg_target(&task_vma_reg_info);
}
late_initcall(task_iter_init);

34
kernel/bpf/verifier.c
View File

@ -6132,6 +6132,33 @@ static int set_timer_callback_state(struct bpf_verifier_env *env,
return 0;
}
static int set_find_vma_callback_state(struct bpf_verifier_env *env,
struct bpf_func_state *caller,
struct bpf_func_state *callee,
int insn_idx)
{
/* bpf_find_vma(struct task_struct *task, u64 addr,
* void *callback_fn, void *callback_ctx, u64 flags)
* (callback_fn)(struct task_struct *task,
* struct vm_area_struct *vma, void *callback_ctx);
*/
callee->regs[BPF_REG_1] = caller->regs[BPF_REG_1];
callee->regs[BPF_REG_2].type = PTR_TO_BTF_ID;
__mark_reg_known_zero(&callee->regs[BPF_REG_2]);
callee->regs[BPF_REG_2].btf = btf_vmlinux;
callee->regs[BPF_REG_2].btf_id = btf_task_struct_ids[2];
/* pointer to stack or null */
callee->regs[BPF_REG_3] = caller->regs[BPF_REG_4];
/* unused */
__mark_reg_not_init(env, &callee->regs[BPF_REG_4]);
__mark_reg_not_init(env, &callee->regs[BPF_REG_5]);
callee->in_callback_fn = true;
return 0;
}
static int prepare_func_exit(struct bpf_verifier_env *env, int *insn_idx)
{
struct bpf_verifier_state *state = env->cur_state;
@ -6489,6 +6516,13 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
return -EINVAL;
}
if (func_id == BPF_FUNC_find_vma) {
err = __check_func_call(env, insn, insn_idx_p, meta.subprogno,
set_find_vma_callback_state);
if (err < 0)
return -EINVAL;
}
if (func_id == BPF_FUNC_snprintf) {
err = check_bpf_snprintf_call(env, regs);
if (err < 0)

2
kernel/trace/bpf_trace.c
View File

@ -1208,6 +1208,8 @@ bpf_tracing_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_get_func_ip_proto_tracing;
case BPF_FUNC_get_branch_snapshot:
return &bpf_get_branch_snapshot_proto;
case BPF_FUNC_find_vma:
return &bpf_find_vma_proto;
case BPF_FUNC_trace_vprintk:
return bpf_get_trace_vprintk_proto();
default:

20
tools/include/uapi/linux/bpf.h
View File

@ -4938,6 +4938,25 @@ union bpf_attr {
* **-ENOENT** if symbol is not found.
*
* **-EPERM** if caller does not have permission to obtain kernel address.
*
* long bpf_find_vma(struct task_struct *task, u64 addr, void *callback_fn, void *callback_ctx, u64 flags)
* Description
* Find vma of *task* that contains *addr*, call *callback_fn*
* function with *task*, *vma*, and *callback_ctx*.
* The *callback_fn* should be a static function and
* the *callback_ctx* should be a pointer to the stack.
* The *flags* is used to control certain aspects of the helper.
* Currently, the *flags* must be 0.
*
* The expected callback signature is
*
* long (\*callback_fn)(struct task_struct \*task, struct vm_area_struct \*vma, void \*callback_ctx);
*
* Return
* 0 on success.
* **-ENOENT** if *task->mm* is NULL, or no vma contains *addr*.
* **-EBUSY** if failed to try lock mmap_lock.
* **-EINVAL** for invalid **flags**.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@ -5120,6 +5139,7 @@ union bpf_attr {
FN(trace_vprintk), \
FN(skc_to_unix_sock), \
FN(kallsyms_lookup_name), \
FN(find_vma), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper