Commit 9f14c42d authored Feb 22, 2009 by Anton Blanchard Committed by Benjamin Herrenschmidt Feb 23, 2009

powerpc: Randomise mmap start address



Randomise mmap start address - 8MB on 32bit and 1GB on 64bit tasks.
Until ppc32 uses the mmap.c functionality, this is ppc64 specific.

Before:

# ./test & cat /proc/${!}/maps|tail -2|head -1
f75fe000-f7fff000 rw-p f75fe000 00:00 0
f75fe000-f7fff000 rw-p f75fe000 00:00 0
f75fe000-f7fff000 rw-p f75fe000 00:00 0
f75fe000-f7fff000 rw-p f75fe000 00:00 0
f75fe000-f7fff000 rw-p f75fe000 00:00 0

After:
# ./test & cat /proc/${!}/maps|tail -2|head -1
f718b000-f7b8c000 rw-p f718b000 00:00 0
f7551000-f7f52000 rw-p f7551000 00:00 0
f6ee7000-f78e8000 rw-p f6ee7000 00:00 0
f74d4000-f7ed5000 rw-p f74d4000 00:00 0
f6e9d000-f789e000 rw-p f6e9d000 00:00 0

Similar for 64bit, but with 1GB of scatter:
# ./test & cat /proc/${!}/maps|tail -2|head -1
fffb97b5000-fffb97b6000 rw-p fffb97b5000 00:00 0
fffce9a3000-fffce9a4000 rw-p fffce9a3000 00:00 0
fffeaaf2000-fffeaaf3000 rw-p fffeaaf2000 00:00 0
fffd88ac000-fffd88ad000 rw-p fffd88ac000 00:00 0
fffbc62e000-fffbc62f000 rw-p fffbc62e000 00:00 0

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

parent 13a2cb36

arch/powerpc/mm/mmap.c

+16 −1

Original line number	Diff line number	Diff line
		@@ -24,6 +24,7 @@

		#include <linux/personality.h>
		#include <linux/mm.h>
		#include <linux/random.h>
		#include <linux/sched.h>

		/*
		@@ -45,6 +46,20 @@ static inline int mmap_is_legacy(void)
		return sysctl_legacy_va_layout;
		}

		static unsigned long mmap_rnd(void)
		{
		unsigned long rnd = 0;

		if (current->flags & PF_RANDOMIZE) {
		/* 8MB for 32bit, 1GB for 64bit */
		if (is_32bit_task())
		rnd = (long)(get_random_int() % (1<<(23-PAGE_SHIFT)));
		else
		rnd = (long)(get_random_int() % (1<<(30-PAGE_SHIFT)));
		}
		return rnd << PAGE_SHIFT;
		}

		static inline unsigned long mmap_base(void)
		{
		unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
		@@ -54,7 +69,7 @@ static inline unsigned long mmap_base(void)
		else if (gap > MAX_GAP)
		gap = MAX_GAP;

		return TASK_SIZE - (gap & PAGE_MASK);
		return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
		}

		/*

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