linux-kernel - [PATCH V2 2/3] x86/mm/pti: issue warning when mapping large pmd beyond specifid range

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Message-Id: <20201210143527.2398-2-jiangshanlai@gmail.com>
Date:   Thu, 10 Dec 2020 22:35:25 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH V2 2/3] x86/mm/pti: issue warning when mapping large pmd beyond specifid range

From: Lai Jiangshan <laijs@...ux.alibaba.com>

When PTI_CLONE_PTE, the caller doesn't want to expose pages beyond specifid
range and it worths a warning.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 arch/x86/mm/pti.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 7ee99ef13a99..cd6da1d42ba9 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -356,6 +356,13 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
 			 * caller, so we just simply align it here.
 			 */
 			addr = round_down(addr, PMD_SIZE);
+			/*
+			 * Mapping large pmd beyond [start, end) may expose
+			 * secrets to user-space when it wants to clone ptes
+			 * only.
+			 */
+			WARN_ON_ONCE(level == PTI_CLONE_PTE &&
+				     (addr < start || end < addr + PMD_SIZE));
 
 			target_pmd = pti_user_pagetable_walk_pmd(addr);
 			if (WARN_ON(!target_pmd))
-- 
2.19.1.6.gb485710b