On Sun, 28 Jan 2007, Ken Chen wrote: > > For ia64, the hugetlb address region is reserved at the top of user > space address. Stacks are below that region. Throw in the mix, we > have two stacks, one memory stack that grows down and one register > stack backing store that grows up. These two stacks are always in > pair and grow towards each other. And lastly, we have virtual address > holes in between regions. It's just impossible to grow any of these > two stacks into hugetlb region no matter how I played it. > > So, AFAICS this bug doesn't apply to ia64 (and certainly not x86). The > new check of is_hugepage_only_range() is really a noop for both arches.
Certainly not a problem on x86. But, never mind hugetlb, you still not quite convinced me that there's no problem at all with get_user_pages find_extend_vma growing on ia64. I repeat that ia64_do_page_fault has REGION tests to guard against expanding either kind of stack across into another region. ia64_brk, ia64_mmap_check and arch_get_unmapped_area have RGN_MAP_LIMIT checks. But where is the equivalent paranoia when ptrace calls get_user_pages calls find_extend_vma? If your usual stacks face each other across the same region, they're not going to pose problem. But what if someone mmaps MAP_GROWSDOWN near the base of a region, then uses ptrace to touch an address near the top of the region below? Hugh - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
