linux-kernel - [PATCH] x86: make sure IDT is page aligned

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Message-ID: <20130712183014.GA20551@www.outflux.net>
Date:	Fri, 12 Jul 2013 11:30:14 -0700
From:	Kees Cook <keescook@...omium.org>
To:	linux-kernel@...r.kernel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Borislav Petkov <bp@...e.de>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Seiji Aguchi <seiji.aguchi@....com>,
	PaX Team <pageexec@...email.hu>
Subject: [PATCH] x86: make sure IDT is page aligned

Since the IDT is referenced from a fixmap, make sure it is page aligned.
This avoids the risk of it ever being moved in the bss and having the
fixmap fail.

Signed-off-by: Kees Cook <keescook@...omium.org>
Reported-by: PaX Team <pageexec@...email.hu>
Cc: stable@...r.kernel.org
---
 arch/x86/kernel/head_32.S |    2 +-
 arch/x86/kernel/head_64.S |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
index e65ddc6..3526dd1 100644
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -734,7 +734,7 @@ boot_gdt_descr:
 	.word __BOOT_DS+7
 	.long boot_gdt - __PAGE_OFFSET
 
-	.word 0				# 32-bit align idt_desc.address
+	.word PAGE_SIZE			# page align idt_desc.address
 idt_descr:
 	.word IDT_ENTRIES*8-1		# idt contains 256 entries
 	.long idt_table
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 5e4d8a8..77e6d3e 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -513,7 +513,7 @@ ENTRY(phys_base)
 #include "../../x86/xen/xen-head.S"
 	
 	.section .bss, "aw", @nobits
-	.align L1_CACHE_BYTES
+	.align PAGE_SIZE
 ENTRY(idt_table)
 	.skip IDT_ENTRIES * 16
 
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security
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