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authorJames Bottomley <James.Bottomley@HansenPartnership.com>2012-11-02 12:30:53 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-12-03 11:37:58 -0800
commit6be49c441050e8a63407f32c14cb59dc5324f252 (patch)
tree6849e6b20ac05c557ead34f4fe1561d3a403f3c5
parent9826d22c720e430e632514c2efcdab33704661d2 (diff)
downloadlinux-linaro-stable-6be49c441050e8a63407f32c14cb59dc5324f252.tar.gz
PARISC: fix virtual aliasing issue in get_shared_area()
commit 949a05d03490e39e773e8652ccab9157e6f595b4 upstream. 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> Signed-off-by: James Bottomley <JBottomley@Parallels.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-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 7426e40699bd..f76c10863c62 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) {