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.
Signed-off-by: Song Liu <songliubraving@xxxxxx>
---
include/linux/bpf.h | 1 +
include/uapi/linux/bpf.h | 20 +++++++
kernel/bpf/task_iter.c | 102 ++++++++++++++++++++++++++++++++-
kernel/bpf/verifier.c | 36 ++++++++++++
kernel/trace/bpf_trace.c | 2 +
tools/include/uapi/linux/bpf.h | 19 ++++++
6 files changed, 179 insertions(+), 1 deletion(-)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 31421c74ba081..65def8467b609 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -2109,6 +2109,7 @@ extern const struct bpf_func_proto bpf_for_each_map_elem_proto;
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_find_vma_proto;
const struct bpf_func_proto *tracing_prog_func_proto(
enum bpf_func_id func_id, const struct bpf_prog *prog);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index c108200378834..e1401ae4decc9 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4915,6 +4915,25 @@ union bpf_attr {
* Dynamically cast a *sk* pointer to a *unix_sock* pointer.
* Return
* *sk* if casting is valid, or **NULL** otherwise.
+ *
+ * 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 \*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), \
@@ -5096,6 +5115,7 @@ union bpf_attr {
FN(get_branch_snapshot), \
FN(trace_vprintk), \
FN(skc_to_unix_sock), \
+ FN(find_vma), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index b48750bfba5aa..ad30f2e885356 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c
@@ -8,6 +8,7 @@
#include <linux/fdtable.h>
#include <linux/filter.h>
#include <linux/btf_ids.h>
+#include <linux/irq_work.h>
struct bpf_iter_seq_task_common {
struct pid_namespace *ns;
@@ -21,6 +22,25 @@ struct bpf_iter_seq_task_info {
u32 tid;
};
+/* irq_work to run mmap_read_unlock() */
+struct task_iter_irq_work {
+ struct irq_work irq_work;
+ struct mm_struct *mm;
+};
+
+static DEFINE_PER_CPU(struct task_iter_irq_work, mmap_unlock_work);
+
+static void do_mmap_read_unlock(struct irq_work *entry)
+{
+ struct task_iter_irq_work *work;
+
+ if (WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)))
+ return;
+
+ work = container_of(entry, struct task_iter_irq_work, irq_work);
+ mmap_read_unlock_non_owner(work->mm);
+}
+
static struct task_struct *task_seq_get_next(struct pid_namespace *ns,
u32 *tid,
bool skip_if_dup_files)
@@ -586,9 +606,89 @@ 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 task_iter_irq_work *work = NULL;
+ struct mm_struct *mm = task->mm;
+ struct vm_area_struct *vma;
+ bool irq_work_busy = false;
+ int ret = -ENOENT;
+
+ if (flags)
+ return -EINVAL;
+
+ if (!mm)
+ return -ENOENT;
+
+ /*
+ * Similar to stackmap with build_id support, we cannot simply do
+ * mmap_read_unlock when the irq is disabled. Instead, we need do
+ * the unlock in the irq_work.
+ */
+ 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 mmap_unlock, abort. */
+ irq_work_busy = true;
+ }
+ } else {
+ /*
+ * PREEMPT_RT does not allow to trylock mmap sem in
+ * interrupt disabled context, abort.
+ */
+ irq_work_busy = true;
+ }
+ }
+
+ 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;
+ }
+ 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(¤t->mm->mmap_lock.dep_map, _RET_IP_);
+ irq_work_queue(&work->irq_work);
+ }
+ return ret;
+}
+
+BTF_ID_LIST_SINGLE(btf_find_vma_ids, struct, task_struct)
+
+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_find_vma_ids[0],
+ .arg2_type = ARG_ANYTHING,
+ .arg3_type = ARG_PTR_TO_FUNC,
+ .arg4_type = ARG_PTR_TO_STACK_OR_NULL,
+ .arg5_type = ARG_ANYTHING,
+};
+
static int __init task_iter_init(void)
{
- int ret;
+ struct task_iter_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);
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index c6616e3258038..393ab21529b08 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -6119,6 +6119,35 @@ static int set_timer_callback_state(struct bpf_verifier_env *env,
return 0;
}
+BTF_ID_LIST_SINGLE(btf_set_find_vma_ids, struct, vm_area_struct)
+
+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 start,
+ * void *callback_fn, void *callback_ctx, u64 flags)
+ * (callback_fn)(struct task_struct *task,
+ * struct vm_area_struct *vma, void *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_set_find_vma_ids[0];
+
+ /* 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;
@@ -6476,6 +6505,13 @@ 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)
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index cbcd0d6fca7c7..c95397c55d0e8 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -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:
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index c108200378834..056c00da1b5d6 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4915,6 +4915,24 @@ union bpf_attr {
* Dynamically cast a *sk* pointer to a *unix_sock* pointer.
* Return
* *sk* if casting is valid, or **NULL** otherwise.
+ * 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 \*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), \
@@ -5096,6 +5114,7 @@ union bpf_attr {
FN(get_branch_snapshot), \
FN(trace_vprintk), \
FN(skc_to_unix_sock), \
+ FN(find_vma), \
/* */
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
--
2.30.2
