Messages in this thread Patches in this message | | | From | Song Liu <> | Subject | Re: [GIT pull] x86/pti for 5.4-rc1 | Date | Wed, 18 Sep 2019 10:40:43 +0000 |
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> On Sep 17, 2019, at 4:35 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote: > > On Tue, Sep 17, 2019 at 4:29 PM Song Liu <songliubraving@fb.com> wrote: >> >> How about we just do: >> >> diff --git i/arch/x86/mm/pti.c w/arch/x86/mm/pti.c >> index b196524759ec..0437f65250db 100644 >> --- i/arch/x86/mm/pti.c >> +++ w/arch/x86/mm/pti.c >> @@ -341,6 +341,7 @@ pti_clone_pgtable(unsigned long start, unsigned long end, >> } >> >> if (pmd_large(*pmd) || level == PTI_CLONE_PMD) { >> + WARN_ON_ONCE(addr & ~PMD_MASK); >> target_pmd = pti_user_pagetable_walk_pmd(addr); >> if (WARN_ON(!target_pmd)) >> return; >> >> So it is a "warn and continue" check just for unaligned PMD address. > > The problem there is that the "continue" part can be wrong. > > Admittedly it requires a pretty crazy setup: you first hit a > pmd_large() entry, but the *next* pmd is regular, so you start doing > the per-page cloning. > > And that per-page cloning will be wrong, because it will start in the > middle of the next pmd, because addr wasn't aligned, and the previous > pmd-only clone did > > addr += PMD_SIZE; > > to go to the next case. > > See?
I see. This is tricky.
Maybe we should skip clone of the first unaligned large pmd?
diff --git i/arch/x86/mm/pti.c w/arch/x86/mm/pti.c index 7f2140414440..1dfa69f8196b 100644 --- i/arch/x86/mm/pti.c +++ w/arch/x86/mm/pti.c @@ -343,6 +343,11 @@ pti_clone_pgtable(unsigned long start, unsigned long end, }
if (pmd_large(*pmd) || level == PTI_CLONE_PMD) { + if (WARN_ON_ONCE(addr & ~PMD_MASK)) { + addr = round_up(addr, PMD_SIZE); + continue; + } + target_pmd = pti_user_pagetable_walk_pmd(addr); if (WARN_ON(!target_pmd)) return; Or we can round_down the addr and copy the whole PMD properly:
diff --git i/arch/x86/mm/pti.c w/arch/x86/mm/pti.c index 7f2140414440..bee9881f2e85 100644 --- i/arch/x86/mm/pti.c +++ w/arch/x86/mm/pti.c @@ -343,6 +343,9 @@ pti_clone_pgtable(unsigned long start, unsigned long end, }
if (pmd_large(*pmd) || level == PTI_CLONE_PMD) { + if (WARN_ON_ONCE(addr & ~PMD_MASK)) + addr &= PMD_MASK; + target_pmd = pti_user_pagetable_walk_pmd(addr); if (WARN_ON(!target_pmd)) return; I think the latter is better, but I am not sure.
Thanks, Song
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