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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/kernel/entry-armv.S
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/kernel/entry-armv.S')
-rw-r--r--arch/arm/kernel/entry-armv.S33
1 files changed, 3 insertions, 30 deletions
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 3e1c26eb32b4..3ce377f7251f 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -427,8 +427,7 @@ ENDPROC(__fiq_abt)
.endm
.macro kuser_cmpxchg_check
-#if !defined(CONFIG_CPU_32v6K) && defined(CONFIG_KUSER_HELPERS) && \
- !defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
+#if !defined(CONFIG_CPU_32v6K) && defined(CONFIG_KUSER_HELPERS)
#ifndef CONFIG_MMU
#warning "NPTL on non MMU needs fixing"
#else
@@ -859,20 +858,7 @@ __kuser_helper_start:
__kuser_cmpxchg64: @ 0xffff0f60
-#if defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
-
- /*
- * Poor you. No fast solution possible...
- * The kernel itself must perform the operation.
- * A special ghost syscall is used for that (see traps.c).
- */
- stmfd sp!, {r7, lr}
- ldr r7, 1f @ it's 20 bits
- swi __ARM_NR_cmpxchg64
- ldmfd sp!, {r7, pc}
-1: .word __ARM_NR_cmpxchg64
-
-#elif defined(CONFIG_CPU_32v6K)
+#if defined(CONFIG_CPU_32v6K)
stmfd sp!, {r4, r5, r6, r7}
ldrd r4, r5, [r0] @ load old val
@@ -948,20 +934,7 @@ __kuser_memory_barrier: @ 0xffff0fa0
__kuser_cmpxchg: @ 0xffff0fc0
-#if defined(CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG)
-
- /*
- * Poor you. No fast solution possible...
- * The kernel itself must perform the operation.
- * A special ghost syscall is used for that (see traps.c).
- */
- stmfd sp!, {r7, lr}
- ldr r7, 1f @ it's 20 bits
- swi __ARM_NR_cmpxchg
- ldmfd sp!, {r7, pc}
-1: .word __ARM_NR_cmpxchg
-
-#elif __LINUX_ARM_ARCH__ < 6
+#if __LINUX_ARM_ARCH__ < 6
#ifdef CONFIG_MMU