Commit fa8cbaaf authored by Dan McGee's avatar Dan McGee Committed by Benjamin Herrenschmidt
Browse files

powerpc+sparc64/mm: Remove hack in mmap randomize layout 



Since commit 8a0a9bd4, this comment in mmap_rnd() does not
hold true as the value returned by get_random_int() will in fact be

different every single call. Remove the comment and simplify the code
back to its original desired form.

This reverts commit a5adc91a which is no longer necessary and
also fixes the sparc code that copied this same adjustment.

Signed-off-by: default avatarDan McGee <dpmcgee@gmail.com>
Acked-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 3ce21cdf

arch/powerpc/mm/mmap_64.c

+3 −11
Original line number Diff line number Diff line
@@ -53,14 +53,6 @@ static inline int mmap_is_legacy(void) 
	return sysctl_legacy_va_layout;

}



/*

 * Since get_random_int() returns the same value within a 1 jiffy window,

 * we will almost always get the same randomisation for the stack and mmap

 * region. This will mean the relative distance between stack and mmap will

 * be the same.

 *

 * To avoid this we can shift the randomness by 1 bit.

 */

static unsigned long mmap_rnd(void)

{

	unsigned long rnd = 0;
@@ -68,11 +60,11 @@ static unsigned long mmap_rnd(void) 
	if (current->flags & PF_RANDOMIZE) {

		/* 8MB for 32bit, 1GB for 64bit */

		if (is_32bit_task())

			rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT)));

			rnd = (long)(get_random_int() % (1<<(23-PAGE_SHIFT)));

		else

			rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT)));

			rnd = (long)(get_random_int() % (1<<(30-PAGE_SHIFT)));

	}

	return (rnd << PAGE_SHIFT) * 2;

	return rnd << PAGE_SHIFT;

}



static inline unsigned long mmap_base(void)

arch/sparc/kernel/sys_sparc_64.c

+3 −3
Original line number Diff line number Diff line
@@ -368,11 +368,11 @@ static unsigned long mmap_rnd(void) 
	if (current->flags & PF_RANDOMIZE) {

		unsigned long val = get_random_int();

		if (test_thread_flag(TIF_32BIT))

			rnd = (val % (1UL << (22UL-PAGE_SHIFT)));

			rnd = (val % (1UL << (23UL-PAGE_SHIFT)));

		else

			rnd = (val % (1UL << (29UL-PAGE_SHIFT)));

			rnd = (val % (1UL << (30UL-PAGE_SHIFT)));

	}

	return (rnd << PAGE_SHIFT) * 2;

	return rnd << PAGE_SHIFT;

}



void arch_pick_mmap_layout(struct mm_struct *mm)

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