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x86: standardize mmap_rnd() usage 

In preparation for splitting out ET_DYN ASLR, this refactors the use of
mmap_rnd() to be used similarly to arm, and extracts the checking of
PF_RANDOMIZE.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kees Cook 2015-04-14 15:47:45 -07:00 committed by Linus Torvalds
parent fbbc400f39
commit 82168140bc
1 changed files with 20 additions and 16 deletions
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26
arch/x86/mm/mmap.c
View File

@ -67,22 +67,21 @@ static int mmap_is_legacy(void)
static unsigned long mmap_rnd(void)
{
unsigned long rnd = 0;
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 (current->flags & PF_RANDOMIZE) {
if (mmap_is_ia32())
rnd = get_random_int() % (1<<8);
rnd = (unsigned long)get_random_int() % (1<<8);
else
rnd = get_random_int() % (1<<28);
}
rnd = (unsigned long)get_random_int() % (1<<28);
return rnd << PAGE_SHIFT;
}
static unsigned long mmap_base(void)
static unsigned long mmap_base(unsigned long rnd)
{
unsigned long gap = rlimit(RLIMIT_STACK);
@ -91,19 +90,19 @@ static unsigned long mmap_base(void)
else if (gap > MAX_GAP)
gap = MAX_GAP;
return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
return PAGE_ALIGN(TASK_SIZE - gap - rnd);
}
/*
* Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
* does, but not when emulating X86_32
*/
static unsigned long mmap_legacy_base(void)
static unsigned long mmap_legacy_base(unsigned long rnd)
{
if (mmap_is_ia32())
return TASK_UNMAPPED_BASE;
else
return TASK_UNMAPPED_BASE + mmap_rnd();
return TASK_UNMAPPED_BASE + rnd;
}
/*
@ -112,13 +111,18 @@ static unsigned long mmap_legacy_base(void)
*/
void arch_pick_mmap_layout(struct mm_struct *mm)
{
mm->mmap_legacy_base = mmap_legacy_base();
mm->mmap_base = mmap_base();
unsigned long random_factor = 0UL;
if (current->flags & PF_RANDOMIZE)
random_factor = mmap_rnd();
mm->mmap_legacy_base = mmap_legacy_base(random_factor);
if (mmap_is_legacy()) {
mm->mmap_base = mm->mmap_legacy_base;
mm->get_unmapped_area = arch_get_unmapped_area;
} else {
mm->mmap_base = mmap_base(random_factor);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
}
}