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ARM: 8155/1: place sigpage at a random offset above stack

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The sigpage is currently placed alongside shared libraries etc in the
address space.  Similar to what x86_64 does for its VDSO, place the
sigpage at a randomized offset above the stack so that learning the
base address of the sigpage doesn't help expose where shared libraries
are loaded in the address space (and vice versa).

Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
This commit is contained in:
Nathan Lynch 2014-09-22 22:12:35 +01:00 committed by Russell King
parent 02e0409a65
commit 389522b0c0
1 changed files with 36 additions and 1 deletions
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37
arch/arm/kernel/process.c
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@ -475,6 +475,39 @@ const char *arch_vma_name(struct vm_area_struct *vma)
return is_gate_vma(vma) ? "[vectors]" : NULL;
}
/* If possible, provide a placement hint at a random offset from the
* stack for the signal page.
*/
static unsigned long sigpage_addr(const struct mm_struct *mm,
unsigned int npages)
{
unsigned long offset;
unsigned long first;
unsigned long last;
unsigned long addr;
unsigned int slots;
first = PAGE_ALIGN(mm->start_stack);
last = TASK_SIZE - (npages << PAGE_SHIFT);
/* No room after stack? */
if (first > last)
return 0;
/* Just enough room? */
if (first == last)
return first;
slots = ((last - first) >> PAGE_SHIFT) + 1;
offset = get_random_int() % slots;
addr = first + (offset << PAGE_SHIFT);
return addr;
}
static struct page *signal_page;
extern struct page *get_signal_page(void);
@ -488,6 +521,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;
unsigned long addr;
unsigned long hint;
int ret = 0;
if (!signal_page)
@ -496,7 +530,8 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
return -ENOMEM;
down_write(&mm->mmap_sem);
addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
hint = sigpage_addr(mm, 1);
addr = get_unmapped_area(NULL, hint, PAGE_SIZE, 0, 0);
if (IS_ERR_VALUE(addr)) {
ret = addr;
goto up_fail;