Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758462Ab2EDOKX (ORCPT ); Fri, 4 May 2012 10:10:23 -0400 Received: from rcsinet15.oracle.com ([148.87.113.117]:18085 "EHLO rcsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758338Ab2EDOKT (ORCPT ); Fri, 4 May 2012 10:10:19 -0400 From: Konrad Rzeszutek Wilk To: xen-devel@lists.xensource.com, linux-kernel@vger.kernel.org Cc: Konrad Rzeszutek Wilk Subject: [PATCH 3/4] xen/pte: Fix crashes when trying to see non-existent PGD/PMD/PUD/PTEs Date: Fri, 4 May 2012 10:04:26 -0400 Message-Id: <1336140267-7399-4-git-send-email-konrad.wilk@oracle.com> X-Mailer: git-send-email 1.7.7.5 In-Reply-To: <1336140267-7399-1-git-send-email-konrad.wilk@oracle.com> References: <1336140267-7399-1-git-send-email-konrad.wilk@oracle.com> X-Source-IP: acsinet22.oracle.com [141.146.126.238] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2002 Lines: 57 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 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. In this case the ptdump_show bitshifts it and we get this invalid value. Instead of doing all of that, we detect the ~0 case and just return !_PAGE_PRESENT. Signed-off-by: Konrad Rzeszutek Wilk --- arch/x86/xen/mmu.c | 7 ++++++- 1 files changed, 6 insertions(+), 1 deletions(-) diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index b8e2794..69f5857 100644 --- 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 val) { 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; -- 1.7.7.5 -- 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/