[patch V2 1/2] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable()

[Thomas Gleixner <tglx@linutronix.de>]

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 independent
   of the mapping level (PUD/PMD/PTE) the next higher mapping
   exist.

If that's not the case the unaligned address can be incremented by PUD or
PMD size wrongly. All callers supply mapped and/or aligned addresses, but
for robustness sake, it's better to handle that case proper 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
---
 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;
 		}