Adding interface to add special mapping for user space page that will be
used as place holder for uprobe trampoline in following changes.
The get_tramp_area(vaddr) function either finds 'callable' page or create
new one. The 'callable' means it's reachable by call instruction (from
vaddr argument) and is decided by each arch via new arch_uprobe_is_callable
function.
The put_tramp_area function either drops refcount or destroys the special
mapping and all the maps are clean up when the process goes down.
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
---
include/linux/uprobes.h | 12 ++++
kernel/events/uprobes.c | 141 ++++++++++++++++++++++++++++++++++++++++
kernel/fork.c | 2 +
3 files changed, 155 insertions(+)
diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
index be306028ed59..222d8e82cee2 100644
--- a/include/linux/uprobes.h
+++ b/include/linux/uprobes.h
@@ -172,6 +172,15 @@ struct xol_area;
struct uprobes_state {
struct xol_area *xol_area;
+ struct hlist_head tramp_head;
+ struct mutex tramp_mutex;
+};
+
+struct tramp_area {
+ unsigned long vaddr;
+ struct page *page;
+ struct hlist_node node;
+ refcount_t ref;
};
extern void __init uprobes_init(void);
@@ -219,6 +228,9 @@ extern int uprobe_verify_opcode(struct page *page, unsigned long vaddr, uprobe_o
extern int arch_uprobe_verify_opcode(struct page *page, unsigned long vaddr,
uprobe_opcode_t *new_opcode, void *data);
extern bool arch_uprobe_is_register(uprobe_opcode_t *insn, int len, void *data);
+struct tramp_area *get_tramp_area(unsigned long vaddr);
+void put_tramp_area(struct tramp_area *area);
+bool arch_uprobe_is_callable(unsigned long vtramp, unsigned long vaddr);
#else /* !CONFIG_UPROBES */
struct uprobes_state {
};
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 944d9df1f081..a44305c559a4 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -616,6 +616,145 @@ set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long v
(uprobe_opcode_t *)&auprobe->insn, UPROBE_SWBP_INSN_SIZE, NULL);
}
+bool __weak arch_uprobe_is_callable(unsigned long vtramp, unsigned long vaddr)
+{
+ return false;
+}
+
+static unsigned long find_nearest_page(unsigned long vaddr)
+{
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *vma, *prev;
+ VMA_ITERATOR(vmi, mm, 0);
+
+ prev = vma_next(&vmi);
+ vma = vma_next(&vmi);
+ while (vma) {
+ if (vma->vm_start - prev->vm_end >= PAGE_SIZE &&
+ arch_uprobe_is_callable(prev->vm_end, vaddr))
+ return prev->vm_end;
+
+ prev = vma;
+ vma = vma_next(&vmi);
+ }
+
+ return 0;
+}
+
+static vm_fault_t tramp_fault(const struct vm_special_mapping *sm,
+ struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+ struct hlist_head *head = &vma->vm_mm->uprobes_state.tramp_head;
+ struct tramp_area *area;
+
+ hlist_for_each_entry(area, head, node) {
+ if (vma->vm_start == area->vaddr) {
+ vmf->page = area->page;
+ get_page(vmf->page);
+ return 0;
+ }
+ }
+
+ return -EINVAL;
+}
+
+static int tramp_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma)
+{
+ return -EPERM;
+}
+
+static const struct vm_special_mapping tramp_mapping = {
+ .name = "[uprobes-trampoline]",
+ .fault = tramp_fault,
+ .mremap = tramp_mremap,
+};
+
+static struct tramp_area *create_tramp_area(unsigned long vaddr)
+{
+ struct mm_struct *mm = current->mm;
+ struct vm_area_struct *vma;
+ struct tramp_area *area;
+
+ vaddr = find_nearest_page(vaddr);
+ if (!vaddr)
+ return NULL;
+
+ area = kzalloc(sizeof(*area), GFP_KERNEL);
+ if (unlikely(!area))
+ return NULL;
+
+ area->page = alloc_page(GFP_HIGHUSER);
+ if (!area->page)
+ goto free_area;
+
+ refcount_set(&area->ref, 1);
+ area->vaddr = vaddr;
+
+ vma = _install_special_mapping(mm, area->vaddr, PAGE_SIZE,
+ VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_DONTCOPY|VM_IO,
+ &tramp_mapping);
+ if (!IS_ERR(vma))
+ return area;
+
+ __free_page(area->page);
+ free_area:
+ kfree(area);
+ return NULL;
+}
+
+struct tramp_area *get_tramp_area(unsigned long vaddr)
+{
+ struct uprobes_state *state = ¤t->mm->uprobes_state;
+ struct tramp_area *area = NULL;
+
+ mutex_lock(&state->tramp_mutex);
+ hlist_for_each_entry(area, &state->tramp_head, node) {
+ if (arch_uprobe_is_callable(area->vaddr, vaddr)) {
+ refcount_inc(&area->ref);
+ goto unlock;
+ }
+ }
+
+ area = create_tramp_area(vaddr);
+ if (area)
+ hlist_add_head(&area->node, &state->tramp_head);
+
+unlock:
+ mutex_unlock(&state->tramp_mutex);
+ return area;
+}
+
+static void destroy_tramp_area(struct tramp_area *area)
+{
+ hlist_del(&area->node);
+ put_page(area->page);
+ kfree(area);
+}
+
+void put_tramp_area(struct tramp_area *area)
+{
+ struct mm_struct *mm = current->mm;
+ struct uprobes_state *state = &mm->uprobes_state;
+
+ if (area == NULL)
+ return;
+
+ mutex_lock(&state->tramp_mutex);
+ if (refcount_dec_and_test(&area->ref))
+ destroy_tramp_area(area);
+ mutex_unlock(&state->tramp_mutex);
+}
+
+static void clear_tramp_head(struct mm_struct *mm)
+{
+ struct uprobes_state *state = &mm->uprobes_state;
+ struct tramp_area *area;
+ struct hlist_node *n;
+
+ hlist_for_each_entry_safe(area, n, &state->tramp_head, node)
+ destroy_tramp_area(area);
+}
+
/* uprobe should have guaranteed positive refcount */
static struct uprobe *get_uprobe(struct uprobe *uprobe)
{
@@ -1788,6 +1927,8 @@ void uprobe_clear_state(struct mm_struct *mm)
delayed_uprobe_remove(NULL, mm);
mutex_unlock(&delayed_uprobe_lock);
+ clear_tramp_head(mm);
+
if (!area)
return;
diff --git a/kernel/fork.c b/kernel/fork.c
index 89ceb4a68af2..b1fe431e5cce 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1248,6 +1248,8 @@ static void mm_init_uprobes_state(struct mm_struct *mm)
{
#ifdef CONFIG_UPROBES
mm->uprobes_state.xol_area = NULL;
+ mutex_init(&mm->uprobes_state.tramp_mutex);
+ INIT_HLIST_HEAD(&mm->uprobes_state.tramp_head);
#endif
}
--
2.47.0
