x86/mm: Introduce arch_rnd() to compute 32/64 mmap random base (6a0b41d1) · Commits · 戴 / test

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>

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 (12810241024UL + 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)

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