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

["tip-bot2 for Song Liu" <tip-bot2@linutronix.de>]

The following commit has been merged into the x86/pti branch of tip:

Commit-ID:     825d0b73cd7526b0bb186798583fae810091cbac
Gitweb:        https://git.kernel.org/tip/825d0b73cd7526b0bb186798583fae810091cbac
Author:        Song Liu <songliubraving@fb.com>
AuthorDate:    Wed, 28 Aug 2019 23:54:55 +02:00
Committer:     Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Thu, 29 Aug 2019 20:52:52 +02:00

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

---
 arch/x86/mm/pti.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index b196524..a24487b 100644
--- 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;
 		}