• Linus Torvalds's avatar
    x86: don't use 'access_ok()' as a range check in get_user_pages_fast() · 7f818906
    Linus Torvalds authored
    It's really not right to use 'access_ok()', since that is meant for the
    normal "get_user()" and "copy_from/to_user()" accesses, which are done
    through the TLB, rather than through the page tables.
    
    Why? access_ok() does both too few, and too many checks.  Too many,
    because it is meant for regular kernel accesses that will not honor the
    'user' bit in the page tables, and because it honors the USER_DS vs
    KERNEL_DS distinction that we shouldn't care about in GUP.  And too few,
    because it doesn't do the 'canonical' check on the address on x86-64,
    since the TLB will do that for us.
    
    So instead of using a function that isn't meant for this, and does
    something else and much more complicated, just do the real rules: we
    don't want the range to overflow, and on x86-64, we want it to be a
    canonical low address (on 32-bit, all addresses are canonical).
    Acked-by: default avatarIngo Molnar <mingo@elte.hu>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    7f818906
gup.c 7.92 KB