On 10/28/21 12:00 AM, Song Liu wrote:
[...]
/* 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;
Won't this NULL deref if called with task argument as NULL?
+ 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);
+ }
Given this is pretty much the same logic around the vma retrieval, could this be
refactored/consolidated with stack map build id retrieval into a common function?
+ 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,
+};
[...]
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)
nit: Wrongly copied uapi header over to tooling?
+ * 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
