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Subject[patch V3 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable()
From: Song Liu <songliubraving@fb.com>

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.

If that's not the case the unaligned address can be incremented by PUD or
PMD size incorrectly. All callers supply mapped and/or aligned addresses,
but for the sake of robustness it's better to handle that case properly and
to emit a warning.

[ tglx: Rewrote changelog and added WARN_ON_ONCE() ]

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V2: Negate P[UM]D_MASK for checking whether the offset part is 0
V3: Fix changelog
---
arch/x86/mm/pti.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -330,13 +330,15 @@ pti_clone_pgtable(unsigned long start, u

pud = pud_offset(p4d, addr);
if (pud_none(*pud)) {
- addr += PUD_SIZE;
+ WARN_ON_ONCE(addr & ~PUD_MASK);
+ addr = round_up(addr + 1, PUD_SIZE);
continue;
}

pmd = pmd_offset(pud, addr);
if (pmd_none(*pmd)) {
- addr += PMD_SIZE;
+ WARN_ON_ONCE(addr & ~PMD_MASK);
+ addr = round_up(addr + 1, PMD_SIZE);
continue;
}

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