Messages in this thread | | | Date | Tue, 25 Jun 2019 22:30:53 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH] x86/boot/64: Fix crash if kernel images crosses page table boundary |
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On Tue, Jun 25, 2019 at 09:04:39PM +0200, Thomas Gleixner wrote: > On Thu, 20 Jun 2019, Kirill A. Shutemov wrote: > > @@ -190,18 +190,18 @@ unsigned long __head __startup_64(unsigned long physaddr, > > pgd[i + 0] = (pgdval_t)p4d + pgtable_flags; > > pgd[i + 1] = (pgdval_t)p4d + pgtable_flags; > > > > - i = (physaddr >> P4D_SHIFT) % PTRS_PER_P4D; > > - p4d[i + 0] = (pgdval_t)pud + pgtable_flags; > > - p4d[i + 1] = (pgdval_t)pud + pgtable_flags; > > + i = physaddr >> P4D_SHIFT; > > + p4d[(i + 0) % PTRS_PER_P4D] = (pgdval_t)pud + pgtable_flags; > > + p4d[(i + 1) % PTRS_PER_P4D] = (pgdval_t)pud + pgtable_flags; > > } else { > > i = (physaddr >> PGDIR_SHIFT) % PTRS_PER_PGD; > > pgd[i + 0] = (pgdval_t)pud + pgtable_flags; > > pgd[i + 1] = (pgdval_t)pud + pgtable_flags; > > } > > > > - i = (physaddr >> PUD_SHIFT) % PTRS_PER_PUD; > > - pud[i + 0] = (pudval_t)pmd + pgtable_flags; > > - pud[i + 1] = (pudval_t)pmd + pgtable_flags; > > + i = physaddr >> PUD_SHIFT; > > + pud[(i + 0) % PTRS_PER_PUD] = (pudval_t)pmd + pgtable_flags; > > + pud[(i + 1) % PTRS_PER_PUD] = (pudval_t)pmd + pgtable_flags; > > > > pmd_entry = __PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL; > > /* Filter out unsupported __PAGE_KERNEL_* bits: */ > > @@ -211,8 +211,8 @@ unsigned long __head __startup_64(unsigned long physaddr, > > pmd_entry += physaddr; > > > > for (i = 0; i < DIV_ROUND_UP(_end - _text, PMD_SIZE); i++) { > > - int idx = i + (physaddr >> PMD_SHIFT) % PTRS_PER_PMD; > > - pmd[idx] = pmd_entry + i * PMD_SIZE; > > + int idx = i + (physaddr >> PMD_SHIFT);; > > double semicolon
Will fix.
> > + pmd[idx % PTRS_PER_PMD] = pmd_entry + i * PMD_SIZE; > > This part is functionally equivivalent. So what's the value of this change?
Precedence of operators were broken
idx = i + (physaddr >> PMD_SHIFT) % PTRS_PER_PMD;
reads by compiler as
idx = i + ((physaddr >> PMD_SHIFT) % PTRS_PER_PMD);
not as
idx = (i + (physaddr >> PMD_SHIFT)) % PTRS_PER_PMD;
Therefore 'idx' can become >= PTRS_PER_PMD.
-- Kirill A. Shutemov
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