linux-kernel - [PATCH] x86/mm/pti: Handle unaligned addr to PMD-mapped page in pti_clone

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Message-ID: <20190919055312.3020652-1-songliubraving@fb.com>
Date:   Wed, 18 Sep 2019 22:53:12 -0700
From:   Song Liu <songliubraving@...com>
To:     <linux-kernel@...r.kernel.org>
CC:     Song Liu <songliubraving@...com>, <kernel-team@...com>,
        <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH] x86/mm/pti: Handle unaligned addr to PMD-mapped page in pti_clone_pgtable

To clone page table of PMD-mapped pages, pti_clone_pgtable() requires PMD
aligned start address. [1] adds warning for unaligned addresses. However,
there is still no warning for unaligned address to valid huge pmd [2].

Add alignment check in valid pmd_large() case. If the address is
unaligned, round it down to the nearest PMD aligned address and show
warning.

[1] commit 825d0b73cd75 ("x86/mm/pti: Handle unaligned address gracefully
                          in pti_clone_pagetable()")
[2] https://lore.kernel.org/lkml/156864062019.3407.14798418565580024723.tglx@nanos.tec.linutronix.de/

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Song Liu <songliubraving@...com>
---
 arch/x86/mm/pti.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 7f2140414440..d224115c350d 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -343,6 +343,10 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
 		}
 
 		if (pmd_large(*pmd) || level == PTI_CLONE_PMD) {
+			/* warn and round_down() unaligned addr */
+			if (WARN_ON_ONCE(addr & ~PMD_MASK))
+				addr &= PMD_MASK;
+
 			target_pmd = pti_user_pagetable_walk_pmd(addr);
 			if (WARN_ON(!target_pmd))
 				return;
-- 
2.17.1