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 <songliubraving@fb.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908282352470.1938@nanos.tec.linutronix.de

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index b196524759ec57b1cce790fff4d807765df8900d..a24487bbc2c4e6ead4bd6b712402bf196592574e 100644 (file)
--- a/arch/x86/mm/pti.c
+++ b/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;
                }