x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable()

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 <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Ingo Molnar <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

arch/x86/mm/pti.c

@@ -330,13 +330,15 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
 
 		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;
 		}