From: Konrad Rzeszutek Wilk Date: Thu, 3 May 2012 20:14:14 +0000 (-0400) Subject: xen/pte: Fix crashes when trying to see non-existent PGD/PMD/PUD/PTEs X-Git-Tag: v3.4-rc7~26^2~2 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b7e5ffe5d83fa40d702976d77452004abbe35791;p=pandora-kernel.git xen/pte: Fix crashes when trying to see non-existent PGD/PMD/PUD/PTEs 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!) CC: stable@kernel.org Signed-off-by: Konrad Rzeszutek Wilk --- Reading git-diff-tree failed