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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: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Dmitry 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: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Dmitry Safonov 2017-03-06 17:17:17 +03:00 committed by Thomas Gleixner
parent 4495c08e84
commit 6a0b41d1e2
1 changed files with 14 additions and 12 deletions
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26
arch/x86/mm/mmap.c
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@ -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;
}
static unsigned long arch_rnd(unsigned int rndbits)
{
return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
}
unsigned long arch_mmap_rnd(void)
{
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 rnd << PAGE_SHIFT;
return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
}
static unsigned long mmap_base(unsigned long rnd)