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FROMLIST: x86: mm: support ARCH_MMAP_RND_BITS.

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(cherry picked from commit https://lkml.org/lkml/2015/12/21/339)

x86: arch_mmap_rnd() uses hard-coded values, 8 for 32-bit and 28 for
64-bit, to generate the random offset for the mmap base address.
This value represents a compromise between increased ASLR
effectiveness and avoiding address-space fragmentation. Replace it
with a Kconfig option, which is sensibly bounded, so that platform
developers may choose where to place this compromise. Keep default
values as new minimums.

Bug: 24047224
Signed-off-by: Daniel Cashman <dcashman@android.com>
Signed-off-by: Daniel Cashman <dcashman@google.com>
Change-Id: Ic38735a8de2943843a73b5c20855ccfa92513422
This commit is contained in:
dcashman 2016-01-12 09:51:16 -08:00 • committed by John Stultz
parent e2240a15c1
commit d51891f0fd
2 changed files with 22 additions and 6 deletions
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16
arch/x86/Kconfig
View file

@ -46,6 +46,8 @@ config X86
select ARCH_WANTS_DYNAMIC_TASK_STRUCT select ARCH_WANTS_DYNAMIC_TASK_STRUCT
select ARCH_WANT_FRAME_POINTERS select ARCH_WANT_FRAME_POINTERS
select ARCH_WANT_IPC_PARSE_VERSION if X86_32 select ARCH_WANT_IPC_PARSE_VERSION if X86_32
select HAVE_ARCH_MMAP_RND_BITS if MMU
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT
select ARCH_WANT_OPTIONAL_GPIOLIB select ARCH_WANT_OPTIONAL_GPIOLIB
select BUILDTIME_EXTABLE_SORT select BUILDTIME_EXTABLE_SORT
select CLKEVT_I8253 select CLKEVT_I8253
@ -183,6 +185,20 @@ config HAVE_LATENCYTOP_SUPPORT
config MMU config MMU
def_bool y def_bool y
config ARCH_MMAP_RND_BITS_MIN
default 28 if 64BIT
default 8
config ARCH_MMAP_RND_BITS_MAX
default 32 if 64BIT
default 16
config ARCH_MMAP_RND_COMPAT_BITS_MIN
default 8
config ARCH_MMAP_RND_COMPAT_BITS_MAX
default 16
config SBUS config SBUS
bool bool

12
arch/x86/mm/mmap.c
View file

@ -69,14 +69,14 @@ unsigned long arch_mmap_rnd(void)
{ {
unsigned long rnd; unsigned long rnd;
/*
* 8 bits of randomness in 32bit mmaps, 20 address space bits
* 28 bits of randomness in 64bit mmaps, 40 address space bits
*/
if (mmap_is_ia32()) if (mmap_is_ia32())
rnd = (unsigned long)get_random_int() % (1<<8); #ifdef CONFIG_COMPAT
rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_compat_bits) - 1);
#else
rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);
#endif
else else
rnd = (unsigned long)get_random_int() % (1<<28); rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);
return rnd << PAGE_SHIFT; return rnd << PAGE_SHIFT;
} }