[PATCH v4 04/10] mips: extract logic for mmap_rnd()
From: Kees Cook <hidden>
Date: 2015-03-04 21:10:48
Also in:
linux-arm-kernel, linux-fsdevel, linux-mips, lkml
Subsystem:
mips, the rest · Maintainers:
Thomas Bogendoerfer, Linus Torvalds
In preparation for splitting out ET_DYN ASLR, extract the mmap ASLR selection into a separate function. Signed-off-by: Kees Cook <redacted> --- It seems the entropy gets smaller as the PAGE_SIZE increases. Is this intentional? --- arch/mips/mm/mmap.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-)
diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
index f1baadd56e82..9a4f1f5c1f0e 100644
--- a/arch/mips/mm/mmap.c
+++ b/arch/mips/mm/mmap.c@@ -142,18 +142,26 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp, addr0, len, pgoff, flags, DOWN); } +static unsigned long mmap_rnd(void) +{ + unsigned long rnd; + + rnd = (unsigned long)get_random_int(); + rnd <<= PAGE_SHIFT; + if (TASK_IS_32BIT_ADDR) + rnd &= 0xfffffful; + else + rnd &= 0xffffffful; + + return rnd; +} + void arch_pick_mmap_layout(struct mm_struct *mm) { unsigned long random_factor = 0UL; - if (current->flags & PF_RANDOMIZE) { - random_factor = get_random_int(); - random_factor = random_factor << PAGE_SHIFT; - if (TASK_IS_32BIT_ADDR) - random_factor &= 0xfffffful; - else - random_factor &= 0xffffffful; - } + if (current->flags & PF_RANDOMIZE) + random_factor = mmap_rnd(); if (mmap_is_legacy()) { mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
--
1.9.1