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Commit 5ec78319 authored by Kees Cook's avatar Kees Cook Committed by Trilok Soni
Browse files

x86: standardize mmap_rnd() usage 



In preparation for splitting out ET_DYN ASLR, this refactors the use of
mmap_rnd() to be used similarly to arm, and extracts the checking of
PF_RANDOMIZE.

Change-Id: I57f1a85162fe97034b41a87b05a3142570ba0c8a
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Git-commit: 82168140bc4cec7ec9bad39705518541149ff8b7
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: default avatarSe Wang (Patrick) Oh <sewango@codeaurora.org>
parent 332ec5e7

arch/x86/mm/mmap.c

+20 −16
Original line number Diff line number Diff line
@@ -67,22 +67,21 @@ static int mmap_is_legacy(void) 


static unsigned long mmap_rnd(void)

{

	unsigned long rnd = 0;

	unsigned long rnd;



	/*

	 *  8 bits of randomness in 32bit mmaps, 20 address space bits

	 * 28 bits of randomness in 64bit mmaps, 40 address space bits

	 */

	if (current->flags & PF_RANDOMIZE) {

	if (mmap_is_ia32())

			rnd = get_random_int() % (1<<8);

		rnd = (unsigned long)get_random_int() % (1<<8);

	else

			rnd = get_random_int() % (1<<28);

	}

		rnd = (unsigned long)get_random_int() % (1<<28);



	return rnd << PAGE_SHIFT;

}



static unsigned long mmap_base(void)

static unsigned long mmap_base(unsigned long rnd)

{

	unsigned long gap = rlimit(RLIMIT_STACK);
@@ -91,19 +90,19 @@ static unsigned long mmap_base(void) 
	else if (gap > MAX_GAP)

		gap = MAX_GAP;



	return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());

	return PAGE_ALIGN(TASK_SIZE - gap - rnd);

}



/*

 * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64

 * does, but not when emulating X86_32

 */

static unsigned long mmap_legacy_base(void)

static unsigned long mmap_legacy_base(unsigned long rnd)

{

	if (mmap_is_ia32())

		return TASK_UNMAPPED_BASE;

	else

		return TASK_UNMAPPED_BASE + mmap_rnd();

		return TASK_UNMAPPED_BASE + rnd;

}



/*
@@ -112,13 +111,18 @@ static unsigned long mmap_legacy_base(void) 
 */

void arch_pick_mmap_layout(struct mm_struct *mm)

{

	mm->mmap_legacy_base = mmap_legacy_base();

	mm->mmap_base = mmap_base();

	unsigned long random_factor = 0UL;



	if (current->flags & PF_RANDOMIZE)

		random_factor = mmap_rnd();



	mm->mmap_legacy_base = mmap_legacy_base(random_factor);



	if (mmap_is_legacy()) {

		mm->mmap_base = mm->mmap_legacy_base;

		mm->get_unmapped_area = arch_get_unmapped_area;

	} else {

		mm->mmap_base = mmap_base(random_factor);

		mm->get_unmapped_area = arch_get_unmapped_area_topdown;

	}

}