Re: [PATCH v15 09/17] fs, arm64: untag user pointers in copy_mount_options

On Mon, May 06, 2019 at 06:30:55PM +0200, Andrey Konovalov wrote:

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.

In copy_mount_options a user address is being subtracted from TASK_SIZE. If the address is lower than TASK_SIZE, the size is calculated to not allow the exact_copy_from_user() call to cross TASK_SIZE boundary. However if the address is tagged, then the size will be calculated incorrectly.

Untag the address before subtracting.

Signed-off-by: Andrey Konovalov andreyknvl@google.com

Reviewed-by: Catalin Marinas catalin.marinas@arm.com