Merge branch 'uprobes/core' of git://git.kernel.org/pub/scm/linux/kernel/git/oleg/misc into perf/core

Fix uprobes bugs that happen if fork() is called with pending ret-probes,
from Oleg Nesterov.

Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/uprobes.h

@@ -117,13 +117,13 @@ extern void uprobe_start_dup_mmap(void);
 extern void uprobe_end_dup_mmap(void);
 extern void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm);
 extern void uprobe_free_utask(struct task_struct *t);
-extern void uprobe_copy_process(struct task_struct *t);
+extern void uprobe_copy_process(struct task_struct *t, unsigned long flags);
 extern unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs);
 extern int uprobe_post_sstep_notifier(struct pt_regs *regs);
 extern int uprobe_pre_sstep_notifier(struct pt_regs *regs);
 extern void uprobe_notify_resume(struct pt_regs *regs);
 extern bool uprobe_deny_signal(void);
-extern bool __weak arch_uprobe_skip_sstep(struct arch_uprobe *aup, struct pt_regs *regs);
+extern bool arch_uprobe_skip_sstep(struct arch_uprobe *aup, struct pt_regs *regs);
 extern void uprobe_clear_state(struct mm_struct *mm);
 #else /* !CONFIG_UPROBES */
 struct uprobes_state {
@@ -174,7 +174,7 @@ static inline unsigned long uprobe_get_swbp_addr(struct pt_regs *regs)
 static inline void uprobe_free_utask(struct task_struct *t)
 {
 }
-static inline void uprobe_copy_process(struct task_struct *t)
+static inline void uprobe_copy_process(struct task_struct *t, unsigned long flags)
 {
 }
 static inline void uprobe_clear_state(struct mm_struct *mm)

kernel/events/uprobes.c

@@ -35,6 +35,7 @@
 #include <linux/kdebug.h>	/* notifier mechanism */
 #include "../../mm/internal.h"	/* munlock_vma_page */
 #include <linux/percpu-rwsem.h>
+#include <linux/task_work.h>
 
 #include <linux/uprobes.h>
 
@@ -1096,21 +1097,22 @@ void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned lon
 }
 
 /* Slot allocation for XOL */
-static int xol_add_vma(struct xol_area *area)
+static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
 {
-	struct mm_struct *mm = current->mm;
 	int ret = -EALREADY;
 
 	down_write(&mm->mmap_sem);
 	if (mm->uprobes_state.xol_area)
 		goto fail;
 
-	ret = -ENOMEM;
-	/* Try to map as high as possible, this is only a hint. */
-	area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, PAGE_SIZE, 0, 0);
-	if (area->vaddr & ~PAGE_MASK) {
-		ret = area->vaddr;
-		goto fail;
+	if (!area->vaddr) {
+		/* Try to map as high as possible, this is only a hint. */
+		area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE,
+						PAGE_SIZE, 0, 0);
+		if (area->vaddr & ~PAGE_MASK) {
+			ret = area->vaddr;
+			goto fail;
+		}
 	}
 
 	ret = install_special_mapping(mm, area->vaddr, PAGE_SIZE,
@@ -1120,30 +1122,19 @@ static int xol_add_vma(struct xol_area *area)
 
 	smp_wmb();	/* pairs with get_xol_area() */
 	mm->uprobes_state.xol_area = area;
-	ret = 0;
  fail:
 	up_write(&mm->mmap_sem);
 
 	return ret;
 }
 
-/*
- * get_xol_area - Allocate process's xol_area if necessary.
- * This area will be used for storing instructions for execution out of line.
- *
- * Returns the allocated area or NULL.
- */
-static struct xol_area *get_xol_area(void)
+static struct xol_area *__create_xol_area(unsigned long vaddr)
 {
 	struct mm_struct *mm = current->mm;
-	struct xol_area *area;
 	uprobe_opcode_t insn = UPROBE_SWBP_INSN;
+	struct xol_area *area;
 
-	area = mm->uprobes_state.xol_area;
-	if (area)
-		goto ret;
-
-	area = kzalloc(sizeof(*area), GFP_KERNEL);
+	area = kmalloc(sizeof(*area), GFP_KERNEL);
 	if (unlikely(!area))
 		goto out;
 
@@ -1155,13 +1146,14 @@ static struct xol_area *get_xol_area(void)
 	if (!area->page)
 		goto free_bitmap;
 
-	/* allocate first slot of task's xol_area for the return probes */
+	area->vaddr = vaddr;
+	init_waitqueue_head(&area->wq);
+	/* Reserve the 1st slot for get_trampoline_vaddr() */
 	set_bit(0, area->bitmap);
-	copy_to_page(area->page, 0, &insn, UPROBE_SWBP_INSN_SIZE);
 	atomic_set(&area->slot_count, 1);
-	init_waitqueue_head(&area->wq);
+	copy_to_page(area->page, 0, &insn, UPROBE_SWBP_INSN_SIZE);
 
-	if (!xol_add_vma(area))
+	if (!xol_add_vma(mm, area))
 		return area;
 
 	__free_page(area->page);
@@ -1170,9 +1162,25 @@ static struct xol_area *get_xol_area(void)
  free_area:
 	kfree(area);
  out:
+	return NULL;
+}
+
+/*
+ * get_xol_area - Allocate process's xol_area if necessary.
+ * This area will be used for storing instructions for execution out of line.
+ *
+ * Returns the allocated area or NULL.
+ */
+static struct xol_area *get_xol_area(void)
+{
+	struct mm_struct *mm = current->mm;
+	struct xol_area *area;
+
+	if (!mm->uprobes_state.xol_area)
+		__create_xol_area(0);
+
 	area = mm->uprobes_state.xol_area;
- ret:
-	smp_read_barrier_depends();     /* pairs with wmb in xol_add_vma() */
+	smp_read_barrier_depends();	/* pairs with wmb in xol_add_vma() */
 	return area;
 }
 
@@ -1344,14 +1352,6 @@ void uprobe_free_utask(struct task_struct *t)
 	t->utask = NULL;
 }
 
-/*
- * Called in context of a new clone/fork from copy_process.
- */
-void uprobe_copy_process(struct task_struct *t)
-{
-	t->utask = NULL;
-}
-
 /*
  * Allocate a uprobe_task object for the task if if necessary.
  * Called when the thread hits a breakpoint.
@@ -1367,6 +1367,90 @@ static struct uprobe_task *get_utask(void)
 	return current->utask;
 }
 
+static int dup_utask(struct task_struct *t, struct uprobe_task *o_utask)
+{
+	struct uprobe_task *n_utask;
+	struct return_instance **p, *o, *n;
+
+	n_utask = kzalloc(sizeof(struct uprobe_task), GFP_KERNEL);
+	if (!n_utask)
+		return -ENOMEM;
+	t->utask = n_utask;
+
+	p = &n_utask->return_instances;
+	for (o = o_utask->return_instances; o; o = o->next) {
+		n = kmalloc(sizeof(struct return_instance), GFP_KERNEL);
+		if (!n)
+			return -ENOMEM;
+
+		*n = *o;
+		atomic_inc(&n->uprobe->ref);
+		n->next = NULL;
+
+		*p = n;
+		p = &n->next;
+		n_utask->depth++;
+	}
+
+	return 0;
+}
+
+static void uprobe_warn(struct task_struct *t, const char *msg)
+{
+	pr_warn("uprobe: %s:%d failed to %s\n",
+			current->comm, current->pid, msg);
+}
+
+static void dup_xol_work(struct callback_head *work)
+{
+	kfree(work);
+
+	if (current->flags & PF_EXITING)
+		return;
+
+	if (!__create_xol_area(current->utask->vaddr))
+		uprobe_warn(current, "dup xol area");
+}
+
+/*
+ * Called in context of a new clone/fork from copy_process.
+ */
+void uprobe_copy_process(struct task_struct *t, unsigned long flags)
+{
+	struct uprobe_task *utask = current->utask;
+	struct mm_struct *mm = current->mm;
+	struct callback_head *work;
+	struct xol_area *area;
+
+	t->utask = NULL;
+
+	if (!utask || !utask->return_instances)
+		return;
+
+	if (mm == t->mm && !(flags & CLONE_VFORK))
+		return;
+
+	if (dup_utask(t, utask))
+		return uprobe_warn(t, "dup ret instances");
+
+	/* The task can fork() after dup_xol_work() fails */
+	area = mm->uprobes_state.xol_area;
+	if (!area)
+		return uprobe_warn(t, "dup xol area");
+
+	if (mm == t->mm)
+		return;
+
+	/* TODO: move it into the union in uprobe_task */
+	work = kmalloc(sizeof(*work), GFP_KERNEL);
+	if (!work)
+		return uprobe_warn(t, "dup xol area");
+
+	utask->vaddr = area->vaddr;
+	init_task_work(work, dup_xol_work);
+	task_work_add(t, work, true);
+}
+
 /*
  * Current area->vaddr notion assume the trampoline address is always
  * equal area->vaddr.

kernel/fork.c

@@ -1373,7 +1373,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	INIT_LIST_HEAD(&p->pi_state_list);
 	p->pi_state_cache = NULL;
 #endif
-	uprobe_copy_process(p);
 	/*
 	 * sigaltstack should be cleared when sharing the same VM
 	 */
@@ -1490,6 +1489,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	perf_event_fork(p);
 
 	trace_task_newtask(p, clone_flags);
+	uprobe_copy_process(p, clone_flags);
 
 	return p;