Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760237Ab2EJRdk (ORCPT ); Thu, 10 May 2012 13:33:40 -0400 Received: from mail-pz0-f46.google.com ([209.85.210.46]:45282 "EHLO mail-pz0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760217Ab2EJRdg (ORCPT ); Thu, 10 May 2012 13:33:36 -0400 Message-Id: <20120510173133.337962395@linuxfoundation.org> User-Agent: quilt/0.60-19.1 Date: Thu, 10 May 2012 10:31:36 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Konrad Rzeszutek Wilk Subject: [ 04/52] xen/pte: Fix crashes when trying to see non-existent PGD/PMD/PUD/PTEs In-Reply-To: <20120510173229.GA5678@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2256 Lines: 66 3.3-stable review patch. If anyone has any objections, please let me know. ------------------ From: Konrad Rzeszutek Wilk commit b7e5ffe5d83fa40d702976d77452004abbe35791 upstream. If I try to do "cat /sys/kernel/debug/kernel_page_tables" I end up with: BUG: unable to handle kernel paging request at ffffc7fffffff000 IP: [] ptdump_show+0x221/0x480 PGD 0 Oops: 0000 [#1] SMP CPU 0 .. snip.. RAX: 0000000000000000 RBX: ffffc00000000fff RCX: 0000000000000000 RDX: 0000800000000000 RSI: 0000000000000000 RDI: ffffc7fffffff000 which is due to the fact we are trying to access a PFN that is not accessible to us. The reason (at least in this case) was that PGD[256] is set to __HYPERVISOR_VIRT_START which was setup (by the hypervisor) to point to a read-only linear map of the MFN->PFN array. During our parsing we would get the MFN (a valid one), try to look it up in the MFN->PFN tree and find it invalid and return ~0 as PFN. Then pte_mfn_to_pfn would happilly feed that in, attach the flags and return it back to the caller. 'ptdump_show' bitshifts it and gets and invalid value that it tries to dereference. Instead of doing all of that, we detect the ~0 case and just return !_PAGE_PRESENT. This bug has been in existence .. at least until 2.6.37 (yikes!) Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Greg Kroah-Hartman --- arch/x86/xen/mmu.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -353,8 +353,13 @@ static pteval_t pte_mfn_to_pfn(pteval_t { if (val & _PAGE_PRESENT) { unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT; + unsigned long pfn = mfn_to_pfn(mfn); + pteval_t flags = val & PTE_FLAGS_MASK; - val = ((pteval_t)mfn_to_pfn(mfn) << PAGE_SHIFT) | flags; + if (unlikely(pfn == ~0)) + val = flags & ~_PAGE_PRESENT; + else + val = ((pteval_t)pfn << PAGE_SHIFT) | flags; } return val; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/