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| author | dcashman <dcashman@google.com> | 2015-12-29 15:28:13 -0800 |
|---|---|---|
| committer | Kees Cook <keescook@google.com> | 2016-03-24 15:25:44 -0700 |
| commit | bbdd420328a3b94c64397954943d62ef63a4ad3c (patch) | |
| tree | 43c75c9c461c32b7d07f2484278fa743dcb1e93a | |
| parent | 98b5338d89bd2669ff75b77ccc60108846b4c3c1 (diff) | |
| download | pxa-v3.14-bbdd420328a3b94c64397954943d62ef63a4ad3c.tar.gz | |
BACKPORT: FROMLIST: arm64: mm: support ARCH_MMAP_RND_BITS.
(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.
Signed-off-by: Daniel Cashman <dcashman@android.com>
Signed-off-by: Daniel Cashman <dcashman@google.com>
Bug: 27796957
Patchset: ASLR sysctl
Change-Id: I9192fa3dd0e061066985b48c84d95c88710282db
Signed-off-by: Kees Cook <keescook@google.com>
| -rw-r--r-- | arch/arm64/Kconfig | 21 | ||||
| -rw-r--r-- | arch/arm64/mm/mmap.c | 21 |
2 files changed, 30 insertions, 12 deletions
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 11dfd3f3a22..3c69f7e1215 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -29,6 +29,8 @@ config ARM64 select GENERIC_TIME_VSYSCALL select HARDIRQS_SW_RESEND select HAVE_ARCH_JUMP_LABEL + select HAVE_ARCH_MMAP_RND_BITS + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT select HAVE_ARCH_TRACEHOOK select HAVE_DEBUG_BUGVERBOSE select HAVE_DEBUG_KMEMLEAK @@ -434,6 +436,25 @@ config HW_PERF_EVENTS config SYS_SUPPORTS_HUGETLBFS def_bool y +config ARCH_MMAP_RND_BITS_MIN + default 14 if ARM64_64K_PAGES + default 18 + +# max bits determined by the following formula: +# VA_BITS - PAGE_SHIFT - 3 +# VA_BITS depends on 64K_PAGES, either +# 42 if 64K_PAGES or 39 otherwise +config ARCH_MMAP_RND_BITS_MAX + default 23 if ARM64_64K_PAGES + default 24 + +config ARCH_MMAP_RND_COMPAT_BITS_MIN + default 7 if ARM64_64K_PAGES + default 11 + +config ARCH_MMAP_RND_COMPAT_BITS_MAX + default 16 + config ARCH_WANT_GENERAL_HUGETLB def_bool y diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c index 8ed6cb1a900..ab79843410a 100644 --- a/arch/arm64/mm/mmap.c +++ b/arch/arm64/mm/mmap.c @@ -47,22 +47,19 @@ static int mmap_is_legacy(void) return sysctl_legacy_va_layout; } -/* - * Since get_random_int() returns the same value within a 1 jiffy window, we - * will almost always get the same randomisation for the stack and mmap - * region. This will mean the relative distance between stack and mmap will be - * the same. - * - * To avoid this we can shift the randomness by 1 bit. - */ static unsigned long mmap_rnd(void) { unsigned long rnd = 0; - if (current->flags & PF_RANDOMIZE) - rnd = (long)get_random_int() & (STACK_RND_MASK >> 1); - - return rnd << (PAGE_SHIFT + 1); + if (current->flags & PF_RANDOMIZE) { +#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; } static unsigned long mmap_base(void) |