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authorJonathan Austin <jonathan.austin@arm.com>2013-04-18 18:37:24 +0100
committerJonathan Austin <jonathan.austin@arm.com>2013-06-17 15:13:18 +0100
commit9dfc28b6308096e48b54c28259825a1200f60742 (patch)
tree44e8b6cbe0935b20767bc79099780244d4c6722e /arch/arm/include
parent801bb21c600161c8626d7d9cb649be869ee4dbbe (diff)
downloadlinux-9dfc28b6308096e48b54c28259825a1200f60742.tar.bz2
ARM: mpu: protect the vectors page with an MPU region
Without an MMU it is possible for userspace programs to start executing code in places that they have no business executing. The MPU allows some level of protection against this. This patch protects the vectors page from access by userspace processes. Userspace tasks that dereference a null pointer are already protected by an svc at 0x0 that kills them. However when tasks use an offset from a null pointer (eg a function in a null struct) they miss this carefully placed svc and enter the exception vectors in user mode, ending up in the kernel. This patch causes programs that do this to receive a SEGV instead of happily entering the kernel in user-mode, and hence avoid a 'Bad Mode' panic. As part of this change it is necessary to make sigreturn happen via the stack when there is not an sa_restorer function. This change is invisible to userspace, and irrelevant to code compiled using a uClibc toolchain, which always uses an sa_restorer function. Because we don't get to remap the vectors in !MMU kuser_helpers are not in a defined location, and hence aren't usable. This means we don't need to worry about keeping them accessible from PL0 Signed-off-by: Jonathan Austin <jonathan.austin@arm.com> Reviewed-by: Will Deacon <will.deacon@arm.com> CC: Nicolas Pitre <nico@linaro.org> CC: Catalin Marinas <catalin.marinas@arm.com>
Diffstat (limited to 'arch/arm/include')
-rw-r--r--arch/arm/include/asm/mpu.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/arch/arm/include/asm/mpu.h b/arch/arm/include/asm/mpu.h
index 001483465aa4..c3247cc2fe08 100644
--- a/arch/arm/include/asm/mpu.h
+++ b/arch/arm/include/asm/mpu.h
@@ -46,6 +46,7 @@
#define MPU_PROBE_REGION 0
#define MPU_BG_REGION 1
#define MPU_RAM_REGION 2
+#define MPU_VECTORS_REGION 3
/* Maximum number of regions Linux is interested in */
#define MPU_MAX_REGIONS 16