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Message-ID: <20160216213659.GA47194@davidb.org>
Date: Tue, 16 Feb 2016 14:36:59 -0700
From: David Brown <david.brown@...aro.org>
To: Russell King <linux@....linux.org.uk>
Cc: linux-arm-kernel@...ts.infradead.org,
kernel-hardening@...ts.openwall.com, Ingo Molnar <mingo@...hat.com>,
Kees Cook <keescook@...omium.org>,
Andy Lutomirski <luto@...capital.net>,
"H. Peter Anvin" <hpa@...or.com>,
Michael Ellerman <mpe@...erman.id.au>,
Mathias Krause <minipli@...glemail.com>,
Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
Arnd Bergmann <arnd@...db.de>, PaX Team <pageexec@...email.hu>,
Emese Revfy <re.emese@...il.com>, linux-kernel@...r.kernel.org,
linux-arch <linux-arch@...r.kernel.org>
Subject: [PATCH] ARM: vdso: Mark vDSO code as read-only
Although the arm vDSO is cleanly separated by code/data with the code
being read-only in userspace mappings, the code page is still writable
from the kernel. There have been exploits (such as
http://itszn.com/blog/?p=21) that take advantage of this on x86 to go
from a bad kernel write to full root.
Prevent this specific exploit on arm by putting the vDSO code page in
post-init read-only memory as well.
Before:
vdso: 1 text pages at base 80927000
root@...press:/ cat /sys/kernel/debug/kernel_page_tables
---[ Modules ]---
---[ Kernel Mapping ]---
0x80000000-0x80100000 1M RW NX SHD
0x80100000-0x80600000 5M ro x SHD
0x80600000-0x80800000 2M ro NX SHD
0x80800000-0xbe000000 984M RW NX SHD
After:
vdso: 1 text pages at base 8072b000
root@...press:/ cat /sys/kernel/debug/kernel_page_tables
---[ Modules ]---
---[ Kernel Mapping ]---
0x80000000-0x80100000 1M RW NX SHD
0x80100000-0x80600000 5M ro x SHD
0x80600000-0x80800000 2M ro NX SHD
0x80800000-0xbe000000 984M RW NX SHD
Inspired by https://lkml.org/lkml/2016/1/19/494 based on work by the
PaX Team, Brad Spengler, and Kees Cook.
Signed-off-by: David Brown <david.brown@...aro.org>
---
This patch depends on Kees Cook's series
https://lkml.org/lkml/2016/1/19/497 which adds the ro_after_init
section.
arch/arm/vdso/vdso.S | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/arch/arm/vdso/vdso.S b/arch/arm/vdso/vdso.S
index b2b97e3..a62a7b6 100644
--- a/arch/arm/vdso/vdso.S
+++ b/arch/arm/vdso/vdso.S
@@ -23,9 +23,8 @@
#include <linux/const.h>
#include <asm/page.h>
- __PAGE_ALIGNED_DATA
-
.globl vdso_start, vdso_end
+ .section .data..ro_after_init
.balign PAGE_SIZE
vdso_start:
.incbin "arch/arm/vdso/vdso.so"
--
2.7.1
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