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authorRussell King <rmk+kernel@arm.linux.org.uk>2015-09-21 19:34:28 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2015-10-03 16:36:45 +0100
commitdb695c0509d6ec9046ee5e4c520a19fa17d9fce2 (patch)
tree450931f1b93e62351049933a916ed5ac1037d236 /arch/arm/mm
parent6f56a68d0bed16c13e9ec958cd28acbc2991d495 (diff)
downloadlinux-linaro-stable-db695c0509d6ec9046ee5e4c520a19fa17d9fce2.tar.gz
ARM: remove user cmpxchg syscall
Mark Brand reports that a NEEDS_SYSCALL_FOR_CMPXCHG enabled kernel would open a security hole in the ghost syscall used to implement cmpxchg, as it fails to validate the user pointer. However, in order for this option to be enabled, you'd need to be building a pre-ARMv6 kernel with SMP support. There is only one system known which fits that, which is an early ARM SMP FPGA implementation based on the ARM926T. In any case, the Kconfig does not allow SMP to be enabled for pre-ARMv6 systems. Moreover, even if NEEDS_SYSCALL_FOR_CMPXCHG were to be enabled, the kernel would not build as __ARM_NR_cmpxchg64 is not defined. The simple answer is to remove the buggy code. Reported-by: Mark Brand <markbrand@google.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/mm')
-rw-r--r--arch/arm/mm/Kconfig12
1 files changed, 0 insertions, 12 deletions
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index df7537f12469..c21941349b3e 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -419,28 +419,24 @@ config CPU_THUMBONLY
config CPU_32v3
bool
select CPU_USE_DOMAINS if MMU
- select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
select NEED_KUSER_HELPERS
select TLS_REG_EMUL if SMP || !MMU
config CPU_32v4
bool
select CPU_USE_DOMAINS if MMU
- select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
select NEED_KUSER_HELPERS
select TLS_REG_EMUL if SMP || !MMU
config CPU_32v4T
bool
select CPU_USE_DOMAINS if MMU
- select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
select NEED_KUSER_HELPERS
select TLS_REG_EMUL if SMP || !MMU
config CPU_32v5
bool
select CPU_USE_DOMAINS if MMU
- select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
select NEED_KUSER_HELPERS
select TLS_REG_EMUL if SMP || !MMU
@@ -805,14 +801,6 @@ config TLS_REG_EMUL
a few prototypes like that in existence) and therefore access to
that required register must be emulated.
-config NEEDS_SYSCALL_FOR_CMPXCHG
- bool
- select NEED_KUSER_HELPERS
- help
- SMP on a pre-ARMv6 processor? Well OK then.
- Forget about fast user space cmpxchg support.
- It is just not possible.
-
config NEED_KUSER_HELPERS
bool