Commit 677b2a8c authored by Christophe Leroy's avatar Christophe Leroy Committed by Linus Torvalds
Browse files

gup: avoid multiple user access locking/unlocking in fault_in_{read/write}able 

fault_in_readable() and fault_in_writeable() perform __get_user() and
__put_user() in a loop, implying multiple user access locking/unlocking.

To avoid that, use user access blocks.

Link: https://lkml.kernel.org/r/720dcf79314acca1a78fae56d478cc851952149d.1637084492.git.christophe.leroy@csgroup.eu


Signed-off-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 43b93121

mm/gup.c

+10 −8
Original line number Diff line number Diff line
@@ -1672,21 +1672,22 @@ size_t fault_in_writeable(char __user *uaddr, size_t size) 


	if (unlikely(size == 0))

		return 0;

	if (!PAGE_ALIGNED(uaddr)) {

		if (unlikely(__put_user(0, uaddr) != 0))

	if (!user_write_access_begin(uaddr, size))

		return size;

	if (!PAGE_ALIGNED(uaddr)) {

		unsafe_put_user(0, uaddr, out);

		uaddr = (char __user *)PAGE_ALIGN((unsigned long)uaddr);

	}

	end = (char __user *)PAGE_ALIGN((unsigned long)start + size);

	if (unlikely(end < start))

		end = NULL;

	while (uaddr != end) {

		if (unlikely(__put_user(0, uaddr) != 0))

			goto out;

		unsafe_put_user(0, uaddr, out);

		uaddr += PAGE_SIZE;

	}



out:

	user_write_access_end();

	if (size > uaddr - start)

		return size - (uaddr - start);

	return 0;
@@ -1771,21 +1772,22 @@ size_t fault_in_readable(const char __user *uaddr, size_t size) 


	if (unlikely(size == 0))

		return 0;

	if (!PAGE_ALIGNED(uaddr)) {

		if (unlikely(__get_user(c, uaddr) != 0))

	if (!user_read_access_begin(uaddr, size))

		return size;

	if (!PAGE_ALIGNED(uaddr)) {

		unsafe_get_user(c, uaddr, out);

		uaddr = (const char __user *)PAGE_ALIGN((unsigned long)uaddr);

	}

	end = (const char __user *)PAGE_ALIGN((unsigned long)start + size);

	if (unlikely(end < start))

		end = NULL;

	while (uaddr != end) {

		if (unlikely(__get_user(c, uaddr) != 0))

			goto out;

		unsafe_get_user(c, uaddr, out);

		uaddr += PAGE_SIZE;

	}



out:

	user_read_access_end();

	(void)c;

	if (size > uaddr - start)

		return size - (uaddr - start);