[PATCH v4 05/10] powerpc: standardize mmap_rnd() usage

Kees Cook
2015-03-04T21:15:40Z

In preparation for splitting out ET_DYN ASLR, this refactors the use of
mmap_rnd() to be used similarly to arm and x86.

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
---
Can mmap ASLR be safely enabled in the legacy mmap case here? Other archs
use "mm->mmap_base = TASK_UNMAPPED_BASE + random_factor".
---
arch/powerpc/mm/mmap.c | 26 +++++++++++++++-----------
1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
index cb8bdbe4972f..1ad2299d795d 100644
--- a/arch/powerpc/mm/mmap.c
+++ b/arch/powerpc/mm/mmap.c
@@ -55,19 +55,18 @@ static inline int mmap_is_legacy(void)

static unsigned long mmap_rnd(void)
{
- unsigned long rnd = 0;
+ unsigned long rnd;
+
+ /* 8MB for 32bit, 1GB for 64bit */
+ if (is_32bit_task())
+ rnd = (unsigned long)get_random_int() % (1<<(23-PAGE_SHIFT));
+ else
+ rnd = (unsigned long)get_random_int() % (1<<(30-PAGE_SHIFT));

- if (current->flags & PF_RANDOMIZE) {
- /* 8MB for 32bit, 1GB for 64bit */
- if (is_32bit_task())
- rnd = (long)(get_random_int() % (1<<(23-PAGE_SHIFT)));
- else
- rnd = (long)(get_random_int() % (1<<(30-PAGE_SHIFT)));
- }
return rnd << PAGE_SHIFT;
}

-static inline unsigned long mmap_base(void)
+static inline unsigned long mmap_base(unsigned long rnd)
{
unsigned long gap = rlimit(RLIMIT_STACK);

@@ -76,7 +75,7 @@ static inline 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);
}

/*
@@ -85,6 +84,11 @@ static inline unsigned long mmap_base(void)
*/
void arch_pick_mmap_layout(struct mm_struct *mm)
{
+ unsigned long random_factor = 0UL;
+
+ if (current->flags & PF_RANDOMIZE)
+ random_factor = mmap_rnd();
+
/*
* Fall back to the standard layout if the personality
* bit is set, or if the expected stack growth is unlimited:
@@ -93,7 +97,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
mm->mmap_base = TASK_UNMAPPED_BASE;
mm->get_unmapped_area = arch_get_unmapped_area;
} else {
- mm->mmap_base = mmap_base();
+ mm->mmap_base = mmap_base(random_factor);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
}
}
--
1.9.1