linux-kernel - [PATCH AUTOSEL 5.2 130/185] x86/mm/pti: Handle unaligned address gracefully in pti_clone

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Message-Id: <20190922184924.32534-130-sashal@kernel.org>
Date:   Sun, 22 Sep 2019 14:48:28 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Song Liu <songliubraving@...com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.2 130/185] x86/mm/pti: Handle unaligned address gracefully in pti_clone_pagetable()

From: Song Liu <songliubraving@...com>

[ Upstream commit 825d0b73cd7526b0bb186798583fae810091cbac ]

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@...com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Ingo Molnar <mingo@...nel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1908282352470.1938@nanos.tec.linutronix.de
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 ba22b50f4eca2..7f2140414440d 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;
 		}
 
-- 
2.20.1