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ARM: allow kuser helpers to be removed from the vector page

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Provide a kernel configuration option to allow the kernel user helpers
to be removed from the vector page, thereby preventing their use with
ROP (return orientated programming) attacks.  This option is only
visible for CPU architectures which natively support all the operations
which kernel user helpers would normally provide, and must be enabled
with caution.

Cc: <stable@vger.kernel.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Russell King 2013-07-23 18:37:00 +01:00
parent e39e3f3ebf
commit f6f91b0d9f
3 changed files with 51 additions and 9 deletions
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3
arch/arm/kernel/entry-armv.S
View File

@ -753,6 +753,7 @@ ENDPROC(__switch_to)
.endr
.endm
#ifdef CONFIG_KUSER_HELPERS
.align 5
.globl __kuser_helper_start
__kuser_helper_start:
@ -939,6 +940,8 @@ __kuser_helper_version: @ 0xffff0ffc
.globl __kuser_helper_end
__kuser_helper_end:
#endif
THUMB( .thumb )
/*

23
arch/arm/kernel/traps.c
View File

@ -800,15 +800,26 @@ void __init trap_init(void)
return;
}
static void __init kuser_get_tls_init(unsigned long vectors)
#ifdef CONFIG_KUSER_HELPERS
static void __init kuser_init(void *vectors)
{
extern char __kuser_helper_start[], __kuser_helper_end[];
int kuser_sz = __kuser_helper_end - __kuser_helper_start;
memcpy(vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);
/*
* vectors + 0xfe0 = __kuser_get_tls
* vectors + 0xfe8 = hardware TLS instruction at 0xffff0fe8
*/
if (tls_emu || has_tls_reg)
memcpy((void *)vectors + 0xfe0, (void *)vectors + 0xfe8, 4);
memcpy(vectors + 0xfe0, vectors + 0xfe8, 4);
}
#else
static void __init kuser_init(void *vectors)
{
}
#endif
void __init early_trap_init(void *vectors_base)
{
@ -816,8 +827,6 @@ void __init early_trap_init(void *vectors_base)
unsigned long vectors = (unsigned long)vectors_base;
extern char __stubs_start[], __stubs_end[];
extern char __vectors_start[], __vectors_end[];
extern char __kuser_helper_start[], __kuser_helper_end[];
int kuser_sz = __kuser_helper_end - __kuser_helper_start;
unsigned i;
vectors_page = vectors_base;
@ -838,12 +847,8 @@ void __init early_trap_init(void *vectors_base)
*/
memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);
memcpy((void *)vectors + 0x1000, __stubs_start, __stubs_end - __stubs_start);
memcpy((void *)vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);
/*
* Do processor specific fixups for the kuser helpers
*/
kuser_get_tls_init(vectors);
kuser_init(vectors_base);
/*
* Copy signal return handlers into the vector page, and

34
arch/arm/mm/Kconfig
View File

@ -421,24 +421,28 @@ config CPU_32v3
select CPU_USE_DOMAINS if MMU
select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
select TLS_REG_EMUL if SMP || !MMU
select NEED_KUSER_HELPERS
config CPU_32v4
bool
select CPU_USE_DOMAINS if MMU
select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
select TLS_REG_EMUL if SMP || !MMU
select NEED_KUSER_HELPERS
config CPU_32v4T
bool
select CPU_USE_DOMAINS if MMU
select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
select TLS_REG_EMUL if SMP || !MMU
select NEED_KUSER_HELPERS
config CPU_32v5
bool
select CPU_USE_DOMAINS if MMU
select NEEDS_SYSCALL_FOR_CMPXCHG if SMP
select TLS_REG_EMUL if SMP || !MMU
select NEED_KUSER_HELPERS
config CPU_32v6
bool
@ -776,6 +780,7 @@ config CPU_BPREDICT_DISABLE
config TLS_REG_EMUL
bool
select NEED_KUSER_HELPERS
help
An SMP system using a pre-ARMv6 processor (there are apparently
a few prototypes like that in existence) and therefore access to
@ -783,11 +788,40 @@ config TLS_REG_EMUL
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
config KUSER_HELPERS
bool "Enable kuser helpers in vector page" if !NEED_KUSER_HELPERS
default y
help
Warning: disabling this option may break user programs.
Provide kuser helpers in the vector page. The kernel provides
helper code to userspace in read only form at a fixed location
in the high vector page to allow userspace to be independent of
the CPU type fitted to the system. This permits binaries to be
run on ARMv4 through to ARMv7 without modification.
However, the fixed address nature of these helpers can be used
by ROP (return orientated programming) authors when creating
exploits.
If all of the binaries and libraries which run on your platform
are built specifically for your platform, and make no use of
these helpers, then you can turn this option off. However,
when such an binary or library is run, it will receive a SIGILL
signal, which will terminate the program.
Say N here only if you are absolutely certain that you do not
need these helpers; otherwise, the safe option is to say Y.
config DMA_CACHE_RWFO
bool "Enable read/write for ownership DMA cache maintenance"
depends on CPU_V6K && SMP