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s390/vdso: add vdso randomization

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Randomize the address of vdso if randomize_va_space is enabled.
Note that this keeps the vdso address on the same PMD as the stack
to avoid allocating an extra page table just for vdso.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
This commit is contained in:
Sven Schnelle 2022-04-06 09:17:21 +02:00 committed by Heiko Carstens
parent 9e37a2e854
commit 41cd81abaf
1 changed files with 32 additions and 1 deletions
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33
arch/s390/kernel/vdso.c
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@ -16,6 +16,7 @@
#include <linux/slab.h>
#include <linux/smp.h>
#include <linux/time_namespace.h>
#include <linux/random.h>
#include <vdso/datapage.h>
#include <asm/vdso.h>
@ -208,6 +209,31 @@ out:
return rc;
}
static unsigned long vdso_addr(unsigned long start, unsigned long len)
{
unsigned long addr, end, offset;
/*
* Round up the start address. It can start out unaligned as a result
* of stack start randomization.
*/
start = PAGE_ALIGN(start);
/* Round the lowest possible end address up to a PMD boundary. */
end = (start + len + PMD_SIZE - 1) & PMD_MASK;
if (end >= VDSO_BASE)
end = VDSO_BASE;
end -= len;
if (end > start) {
offset = get_random_int() % (((end - start) >> PAGE_SHIFT) + 1);
addr = start + (offset << PAGE_SHIFT);
} else {
addr = start;
}
return addr;
}
unsigned long vdso_size(void)
{
unsigned long size = VVAR_NR_PAGES * PAGE_SIZE;
@ -221,7 +247,12 @@ unsigned long vdso_size(void)
int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
return map_vdso(VDSO_BASE, vdso_size());
unsigned long addr = VDSO_BASE;
unsigned long size = vdso_size();
if (current->flags & PF_RANDOMIZE)
addr = vdso_addr(current->mm->start_stack + PAGE_SIZE, size);
return map_vdso(addr, size);
}
static struct page ** __init vdso_setup_pages(void *start, void *end)