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powerpc,mmap: properly account for stack randomization in mmap_base

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When RLIMIT_STACK is, for example, 256MB, the current code results in a
gap between the top of the task and mmap_base of 256MB, failing to take
into account the amount by which the stack address was randomized.  In
other words, the stack gets less than RLIMIT_STACK space.

Ensure that the gap between the stack and mmap_base always takes stack
randomization and the stack guard gap into account.

Inspired by Daniel Micay's linux-hardened tree.

Link: http://lkml.kernel.org/r/20170622200033.25714-4-riel@redhat.com
Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Florian Weimer <fweimer@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Daniel Micay <danielmicay@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rik van Riel 2017-07-12 14:36:39 -07:00 committed by Linus Torvalds
parent cf92251dc5
commit 0a782dc31f
1 changed files with 19 additions and 9 deletions
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28
arch/powerpc/mm/mmap.c
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@ -34,16 +34,9 @@
/*
* Top of mmap area (just below the process stack).
*
* Leave at least a ~128 MB hole on 32bit applications.
*
* On 64bit applications we randomise the stack by 1GB so we need to
* space our mmap start address by a further 1GB, otherwise there is a
* chance the mmap area will end up closer to the stack than our ulimit
* requires.
* Leave at least a ~128 MB hole.
*/
#define MIN_GAP32 (128*1024*1024)
#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
#define MIN_GAP (128*1024*1024)
#define MAX_GAP (TASK_SIZE/6*5)
static inline int mmap_is_legacy(void)
@ -71,9 +64,26 @@ unsigned long arch_mmap_rnd(void)
return rnd << PAGE_SHIFT;
}
static inline unsigned long stack_maxrandom_size(void)
{
if (!(current->flags & PF_RANDOMIZE))
return 0;
/* 8MB for 32bit, 1GB for 64bit */
if (is_32bit_task())
return (1<<23);
else
return (1<<30);
}
static inline unsigned long mmap_base(unsigned long rnd)
{
unsigned long gap = rlimit(RLIMIT_STACK);
unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
/* Values close to RLIM_INFINITY can overflow. */
if (gap + pad > gap)
gap += pad;
if (gap < MIN_GAP)
gap = MIN_GAP;