• James Bottomley's avatar
    [PARISC] fix virtual aliasing issue in get_shared_area() · 949a05d0
    James Bottomley authored
    On Thu, 2012-11-01 at 16:45 -0700, Michel Lespinasse wrote:
    > Looking at the arch/parisc/kernel/sys_parisc.c implementation of
    > get_shared_area(), I do have a concern though. The function basically
    > ignores the pgoff argument, so that if one creates a shared mapping of
    > pages 0-N of a file, and then a separate shared mapping of pages 1-N
    > of that same file, both will have the same cache offset for their
    > starting address.
    >
    > This looks like this would create obvious aliasing issues. Am I
    > misreading this ? I can't understand how this could work good enough
    > to be undetected, so there must be something I'm missing here ???
    
    This turns out to be correct and we need to pay attention to the pgoff as
    well as the address when creating the virtual address for the area.
    Fortunately, the bug is rarely triggered as most applications which use pgoff
    tend to use large values (git being the primary one, and it uses pgoff in
    multiples of 16MB) which are larger than our cache coherency modulus, so the
    problem isn't often seen in practise.
    Reported-by: default avatarMichel Lespinasse <walken@google.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarJames Bottomley <JBottomley@Parallels.com>
    949a05d0
sys_parisc.c 6.85 KB