Messages in this thread | | | Date | Wed, 8 Sep 2021 12:35:21 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v2] x86/mm: fix kern_addr_valid to cope with existing but not present entries |
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On Wed, Aug 25, 2021 at 11:47:10AM -0700, Dave Hansen wrote: > On 8/19/21 6:27 AM, Mike Rapoport wrote: > > Such PMDs are created when free_kernel_image_pages() frees regions larger > > than 2Mb. In this case a part of the freed memory is mapped with PMDs and > > the set_memory_np_noalias() -> ... -> __change_page_attr() sequence will > > mark the PMD as not present rather than wipe it completely. > > > > Make kern_addr_valid() to check whether higher level page table entries are > > present before trying to dereference them to fix this issue and to avoid > > similar issues in the future. > > > > Reported-by: Jiri Olsa <jolsa@redhat.com> > > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com> > > Cc: <stable@vger.kernel.org> # 4.4... > > pmd = pmd_offset(pud, addr); > > - if (pmd_none(*pmd)) > > + if (!pmd_present(*pmd)) > > return 0; > > Yeah, that seems like the right fix. The one kern_addr_valid() user is > going to touch the memory so it *better* be present. p*d_none() was > definitely the wrong check. > > Acked-by: Dave Hansen <dave.hansen@intel.com>
So I did stare at this for a while, trying to make sense of it and David Hildenbrand asked for a Fixes: tag in v1 review and from doing a bit of git archeology I think it should be:
c40a56a7818c ("x86/mm/init: Remove freed kernel image areas from alias mapping")
because that thing added the clearing of the Present bit for the high kernel image mapping of those areas.
Right?
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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