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Commit 0a782dc3 authored by Rik van Riel's avatar Rik van Riel Committed by Linus Torvalds
Browse files

powerpc,mmap: properly account for stack randomization in mmap_base 

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: default avatarRik van Riel <riel@redhat.com>
Reported-by: default avatarFlorian 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cf92251d

arch/powerpc/mm/mmap.c

+19 −9
Original line number Original line Diff line number Diff line
@@ -34,16 +34,9 @@ 
/*

/*

 * Top of mmap area (just below the process stack).

 * Top of mmap area (just below the process stack).

 *

 *

 * Leave at least a ~128 MB hole on 32bit applications.

 * Leave at least a ~128 MB hole.

 *

 * 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.

 */

 */

#define MIN_GAP32 (128*1024*1024)

#define MIN_GAP (128*1024*1024)

#define MIN_GAP64 ((128 + 1024)*1024*1024UL)

#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)

#define MAX_GAP (TASK_SIZE/6*5)

#define MAX_GAP (TASK_SIZE/6*5)





static inline int mmap_is_legacy(void)

static inline int mmap_is_legacy(void)
@@ -71,9 +64,26 @@ unsigned long arch_mmap_rnd(void) 
	return rnd << PAGE_SHIFT;

	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)

static inline unsigned long mmap_base(unsigned long rnd)

{

{

	unsigned long gap = rlimit(RLIMIT_STACK);

	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)

	if (gap < MIN_GAP)

		gap = MIN_GAP;

		gap = MIN_GAP;