[RFC PATCH v2 4/6] mm, arm64: untag user addresses in mm/gup.c

[Andrey Konovalov <andreyknvl@google.com>]

mm/gup.c provides a kernel interface that accepts user addresses and
manipulates user pages directly (for example get_user_pages, that is used
by the futex syscall). Here we also need to handle the case of tagged user
pointers.

Untag addresses passed to this interface.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/gup.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 6afae32571ca..9c4afcf50dfa 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -386,6 +386,8 @@ struct page *follow_page_mask(struct vm_area_struct *vma,
 	struct page *page;
 	struct mm_struct *mm = vma->vm_mm;
 
+	address = untagged_addr(address);
+
 	*page_mask = 0;
 
 	/* make this handle hugepd */
@@ -647,6 +649,8 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 	if (!nr_pages)
 		return 0;
 
+	start = untagged_addr(start);
+
 	VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
 
 	/*
@@ -801,6 +805,8 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
 	struct vm_area_struct *vma;
 	int ret, major = 0;
 
+	address = untagged_addr(address);
+
 	if (unlocked)
 		fault_flags |= FAULT_FLAG_ALLOW_RETRY;
 
@@ -854,6 +860,8 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
 	long ret, pages_done;
 	bool lock_dropped;
 
+	start = untagged_addr(start);
+
 	if (locked) {
 		/* if VM_FAULT_RETRY can be returned, vmas become invalid */
 		BUG_ON(vmas);
@@ -1749,6 +1757,8 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	unsigned long flags;
 	int nr = 0;
 
+	start = untagged_addr(start);
+
 	start &= PAGE_MASK;
 	addr = start;
 	len = (unsigned long) nr_pages << PAGE_SHIFT;
@@ -1801,6 +1811,8 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
 	unsigned long addr, len, end;
 	int nr = 0, ret = 0;
 
+	start = untagged_addr(start);
+
 	start &= PAGE_MASK;
 	addr = start;
 	len = (unsigned long) nr_pages << PAGE_SHIFT;
-- 
2.17.0.rc0.231.g781580f067-goog