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Commit 6a0b41d1 authored by Dmitry Safonov's avatar Dmitry Safonov Committed by Thomas Gleixner
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x86/mm: Introduce arch_rnd() to compute 32/64 mmap random base 



The compat (32bit) mmap() sycall issued by a 64-bit task results in a
mapping above 4GB. That's outside the compat mode address space and
prevents CRIU to restore 32bit processes from a 64bit application.

As a first step to address this, split out the address base randomizing
calculation from arch_mmap_rnd() into a helper function, which can be used
independent of mmap_ia32() based decisions.

[ tglx: Massaged changelog ]

Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarDmitry Safonov <dsafonov@virtuozzo.com>
Cc: 0x7f454c46@gmail.com
Cc: linux-mm@kvack.org
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Borislav Petkov <bp@suse.de>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Link: http://lkml.kernel.org/r/20170306141721.9188-2-dsafonov@virtuozzo.com


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent 4495c08e

arch/x86/mm/mmap.c

+14 −12
Original line number Diff line number Diff line
@@ -55,6 +55,14 @@ static unsigned long stack_maxrandom_size(void) 
#define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())

#define MAX_GAP (TASK_SIZE/6*5)



#ifdef CONFIG_COMPAT

# define mmap32_rnd_bits  mmap_rnd_compat_bits

# define mmap64_rnd_bits  mmap_rnd_bits

#else

# define mmap32_rnd_bits  mmap_rnd_bits

# define mmap64_rnd_bits  mmap_rnd_bits

#endif



static int mmap_is_legacy(void)

{

	if (current->personality & ADDR_COMPAT_LAYOUT)
@@ -66,20 +74,14 @@ static int mmap_is_legacy(void) 
	return sysctl_legacy_va_layout;

}



unsigned long arch_mmap_rnd(void)

static unsigned long arch_rnd(unsigned int rndbits)

{

	unsigned long rnd;



	if (mmap_is_ia32())

#ifdef CONFIG_COMPAT

		rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);

#else

		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);

#endif

	else

		rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);

	return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;

}



	return rnd << PAGE_SHIFT;

unsigned long arch_mmap_rnd(void)

{

	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);

}



static unsigned long mmap_base(unsigned long rnd)