[PATCH v4 03/10] arm64: standardize mmap_rnd() usage

Kees Cook
2015-03-04T21:13:09Z

In preparation for splitting out ET_DYN ASLR, this refactors the use of
mmap_rnd() to be used similarly to arm and x86. This additionally enables
mmap ASLR on legacy mmap layouts, which appeared to be missing on arm64,
and was already supported on arm. Additionally removes a copy/pasted
declaration of an unused function.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/arm64/include/asm/elf.h | 1 -
arch/arm64/mm/mmap.c | 18 +++++++++++-------
2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/elf.h b/arch/arm64/include/asm/elf.h
index 1f65be393139..f724db00b235 100644
--- a/arch/arm64/include/asm/elf.h
+++ b/arch/arm64/include/asm/elf.h
@@ -125,7 +125,6 @@ typedef struct user_fpsimd_state elf_fpregset_t;
* the loader. We need to make sure that it is out of the way of the program
* that it will "exec", and that there is sufficient room for the brk.
*/
-extern unsigned long randomize_et_dyn(unsigned long base);
#define ELF_ET_DYN_BASE (2 * TASK_SIZE_64 / 3)

/*
diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
index 54922d1275b8..ba776c01b552 100644
--- a/arch/arm64/mm/mmap.c
+++ b/arch/arm64/mm/mmap.c
@@ -49,15 +49,14 @@ static int mmap_is_legacy(void)

static unsigned long mmap_rnd(void)
{
- unsigned long rnd = 0;
+ unsigned long rnd;

- if (current->flags & PF_RANDOMIZE)
- rnd = (long)get_random_int() & STACK_RND_MASK;
+ rnd = (unsigned long)get_random_int() & STACK_RND_MASK;

return rnd << PAGE_SHIFT;
}

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

@@ -66,7 +65,7 @@ static unsigned long mmap_base(void)
else if (gap > MAX_GAP)
gap = MAX_GAP;

- return PAGE_ALIGN(STACK_TOP - gap - mmap_rnd());
+ return PAGE_ALIGN(STACK_TOP - gap - rnd);
}

/*
@@ -75,15 +74,20 @@ static 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:
*/
if (mmap_is_legacy()) {
- mm->mmap_base = TASK_UNMAPPED_BASE;
+ mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
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