[PATCH v12 07/13] fs, arm64: untag user pointers in fs/userfaultfd.c

Andrey Konovalov andreyknvl at google.com
Mon Mar 18 10:17:39 PDT 2019

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.

userfaultfd_register() and userfaultfd_unregister() use provided user
pointers for vma lookups, which can only by done with untagged pointers.

Untag user pointers in these functions.

Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
 fs/userfaultfd.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 89800fc7dc9d..a3b70e0d9756 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1320,6 +1320,9 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
 		goto out;
+	uffdio_register.range.start =
+		untagged_addr(uffdio_register.range.start);
 	ret = validate_range(mm, uffdio_register.range.start,
 	if (ret)
@@ -1507,6 +1510,8 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 	if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
 		goto out;
+	uffdio_unregister.start = untagged_addr(uffdio_unregister.start);
 	ret = validate_range(mm, uffdio_unregister.start,
 	if (ret)

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