linux-kernel - [PATCH 2/2] x86/mm/pti: warn and stop when pti_clone

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Message-Id: <20201130152516.2387-2-jiangshanlai@gmail.com>
Date:   Mon, 30 Nov 2020 23:25:16 +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 2/2] x86/mm/pti: warn and stop when pti_clone_pagetable() is on 1G page

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

All callers don't call pti_clone_pagetable() on range that
includes pud large page(1G). If it were called in such
case, there would be bugs in the caller size, so it worth
a warning for robustness.

Also add check for pgd_large() & p4d_large() with the same
reason, and pgd_large() & p4d_large() are constant 0 which
just acts as self-comment in code without overhead.

Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.com>
---
 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 a229320515da..89366fec956b 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -321,10 +321,10 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
 			break;
 
 		pgd = pgd_offset_k(addr);
-		if (WARN_ON(pgd_none(*pgd)))
+		if (WARN_ON(pgd_none(*pgd) || pgd_large(*pgd)))
 			return;
 		p4d = p4d_offset(pgd, addr);
-		if (WARN_ON(p4d_none(*p4d)))
+		if (WARN_ON(p4d_none(*p4d) || p4d_large(*p4d)))
 			return;
 
 		pud = pud_offset(p4d, addr);
@@ -333,6 +333,8 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
 			addr = round_up(addr + 1, PUD_SIZE);
 			continue;
 		}
+		if (WARN_ON(pud_large(*pud)))
+			return;
 
 		pmd = pmd_offset(pud, addr);
 		if (pmd_none(*pmd)) {
-- 
2.19.1.6.gb485710b