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FROMLIST: arm64: mm: support ARCH_MMAP_RND_BITS.

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(cherry picked from commit https://lkml.org/lkml/2015/12/21/340)

arm64: arch_mmap_rnd() uses STACK_RND_MASK 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: I0be0bf8b1ed412863f248323e2d86b1df5bf21c6
This commit is contained in:
dcashman 2016-01-12 09:47:53 -08:00 • committed by John Stultz
parent 25106ff489
commit e2240a15c1
2 changed files with 35 additions and 2 deletions
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29
arch/arm64/Kconfig
View file

@ -51,6 +51,8 @@ config ARM64
select HAVE_ARCH_JUMP_LABEL select HAVE_ARCH_JUMP_LABEL
select HAVE_ARCH_KASAN if SPARSEMEM_VMEMMAP && !(ARM64_16K_PAGES && ARM64_VA_BITS_48) select HAVE_ARCH_KASAN if SPARSEMEM_VMEMMAP && !(ARM64_16K_PAGES && ARM64_VA_BITS_48)
select HAVE_ARCH_KGDB select HAVE_ARCH_KGDB
select HAVE_ARCH_MMAP_RND_BITS
select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ARCH_TRACEHOOK select HAVE_ARCH_TRACEHOOK
select HAVE_BPF_JIT select HAVE_BPF_JIT
@ -104,6 +106,33 @@ config ARCH_PHYS_ADDR_T_64BIT
config MMU config MMU
def_bool y def_bool y
config ARCH_MMAP_RND_BITS_MIN
default 14 if ARM64_64K_PAGES
default 16 if ARM64_16K_PAGES
default 18
# max bits determined by the following formula:
# VA_BITS - PAGE_SHIFT - 3
config ARCH_MMAP_RND_BITS_MAX
default 19 if ARM64_VA_BITS=36
default 24 if ARM64_VA_BITS=39
default 27 if ARM64_VA_BITS=42
default 30 if ARM64_VA_BITS=47
default 29 if ARM64_VA_BITS=48 && ARM64_64K_PAGES
default 31 if ARM64_VA_BITS=48 && ARM64_16K_PAGES
default 33 if ARM64_VA_BITS=48
default 14 if ARM64_64K_PAGES
default 16 if ARM64_16K_PAGES
default 18
config ARCH_MMAP_RND_COMPAT_BITS_MIN
default 7 if ARM64_64K_PAGES
default 9 if ARM64_16K_PAGES
default 11
config ARCH_MMAP_RND_COMPAT_BITS_MAX
default 16
config NO_IOPORT_MAP config NO_IOPORT_MAP
def_bool y if !PCI def_bool y if !PCI

8
arch/arm64/mm/mmap.c
View file

@ -51,8 +51,12 @@ unsigned long arch_mmap_rnd(void)
{ {
unsigned long rnd; unsigned long rnd;
rnd = (unsigned long)get_random_int() & STACK_RND_MASK; #ifdef CONFIG_COMPAT
if (test_thread_flag(TIF_32BIT))
rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_compat_bits) - 1);
else
#endif
rnd = (unsigned long)get_random_int() & ((1 << mmap_rnd_bits) - 1);
return rnd << PAGE_SHIFT; return rnd << PAGE_SHIFT;
} }