This patch is a part of a series that extends arm64 kernel ABI to allow to pass tagged user pointers (with the top byte set to something else other than 0x00) as syscall arguments.
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). Since a user can provided tagged addresses, we need to handle this case.
Add untagging to gup.c functions that use user addresses for vma lookups.
Signed-off-by: Andrey Konovalov andreyknvl@google.com --- mm/gup.c | 4 ++++ 1 file changed, 4 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c index 91819b8ad9cc..2f477a0a7180 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -696,6 +696,8 @@ 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));
/* @@ -858,6 +860,8 @@ int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm, struct vm_area_struct *vma; vm_fault_t ret, major = 0;
+ address = untagged_addr(address); + if (unlocked) fault_flags |= FAULT_FLAG_ALLOW_RETRY;