powerpc,mmap: properly account for stack randomization in mmap_base (0a782dc3) · Commits · 戴 / test

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>

arch/powerpc/mm/mmap.c

+19 −9

Original line number	Diff line number	Diff line
		@@ -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 (12810241024)
		#define MIN_GAP64 ((128 + 1024)10241024UL)
		#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
		#define MIN_GAP (12810241024)
		#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;

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