[PATCH v3 03/10] arm64: standardize mmap_rnd() usage

[Kees Cook]

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 <keesc...@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..837626d0e142 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 base)
 {
        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 - base);
 }
 
 /*
@@ -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

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