From 949a05d03490e39e773e8652ccab9157e6f595b4 Mon Sep 17 00:00:00 2001 From: James Bottomley Date: Fri, 2 Nov 2012 12:30:53 +0000 Subject: [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 Cc: Signed-off-by: James Bottomley --- arch/parisc/kernel/sys_parisc.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/parisc/kernel') diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c index 7426e40..f76c108 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) { -- cgit v1.1