Messages in this thread | | | From | Lai Jiangshan <> | Date | Wed, 2 Dec 2020 16:55:29 +0800 | Subject | Re: [PATCH 1/2] x86/mm/pti: Check unaligned address for pmd clone in pti_clone_pagetable() |
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On Wed, Dec 2, 2020 at 1:43 AM Dave Hansen <dave.hansen@intel.com> wrote: > > On 11/30/20 7:25 AM, Lai Jiangshan wrote: > > The commit 825d0b73cd752("x86/mm/pti: Handle unaligned address gracefully > > in pti_clone_pagetable()") handles unaligned address well for unmapped > > PUD/PMD etc. But unaligned address for pmd_large() or PTI_CLONE_PMD is also > > needed to be aware. > > That 825d0b73cd752 changelog says: > > > pti_clone_pmds() assumes that the supplied address is either: > > > > - properly PUD/PMD aligned > > or > > - the address is actually mapped which means that independently > > of the mapping level (PUD/PMD/PTE) the next higher mapping > > exists. > > ... and that was the root of the bug. If there was a large, unmapped > area, it would skip a PUD_SIZE or PMD_SIZE *area* instead of skipping to > the *next* pud/pmd. > > The case being patched here is from a *present* PTE/PMD, so it's a > mapped area, not a hole. > > That said, I think the previous changelog was wrong. An unaligned > address to a mapped, large (2M) region followed by a smaller (4k) region > would skip too far into the 4k region. > > That said, I'm not sure I like this fix. If someone is explicitly > asking to clone a PMD (which pti_clone_pgtable() forces you to do), they > better align the address.
Hello, Dave
I think I got what you mean more or less, but I don't think I can update the patch to address all your concerns and requirements.
I know very little about the area.
Could you make new patches to replace mine.
Thanks Lai.
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