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

[Catalin Marinas]

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 at google.com>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>