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authorJames Bottomley <James.Bottomley@HansenPartnership.com>2012-11-02 12:30:53 +0000
committerJames Bottomley <JBottomley@Parallels.com>2012-11-15 05:49:34 -0800
commit949a05d03490e39e773e8652ccab9157e6f595b4 (patch)
treef53c84f5ba9b0e5367a99f9560198560f7a3ea3c /arch/parisc/kernel
parent77b67063bb6bce6d475e910d3b886a606d0d91f7 (diff)
downloadvexpress-lsk-949a05d03490e39e773e8652ccab9157e6f595b4.tar.gz
[PARISC] fix virtual aliasing issue in get_shared_area()
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: Michel Lespinasse <walken@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Diffstat (limited to 'arch/parisc/kernel')
-rw-r--r--arch/parisc/kernel/sys_parisc.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
index 7426e40699b..f76c10863c6 100644
--- a/arch/parisc/kernel/sys_parisc.c
+++ b/arch/parisc/kernel/sys_parisc.c
@@ -73,6 +73,8 @@ static unsigned long get_shared_area(struct address_space *mapping,
struct vm_area_struct *vma;
int offset = mapping ? get_offset(mapping) : 0;
+ offset = (offset + (pgoff << PAGE_SHIFT)) & 0x3FF000;
+
addr = DCACHE_ALIGN(addr - offset) + offset;
for (vma = find_vma(current->mm, addr); ; vma = vma->vm_next) {