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powerpc: Randomise lower bits of stack address

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Randomise the lower bits of the stack address. More randomisation is good for
security but the scatter can also help with SMT threads that share an L1. A
quick test case shows this working:

int main()
{
	int sp;
	printf("%x\n", (unsigned long)&sp & 4095);
}

before:
80
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80

after:
610
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6b0
d80

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard 2009-02-22 01:50:03 +00:00 committed by Benjamin Herrenschmidt
parent 2dadb987e0
commit d839088cae
2 changed files with 10 additions and 1 deletions
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2
arch/powerpc/include/asm/system.h
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@ -531,7 +531,7 @@ __cmpxchg_local(volatile void *ptr, unsigned long old, unsigned long new,
#define cmpxchg64_local(ptr, o, n) __cmpxchg64_local_generic((ptr), (o), (n))
#endif
#define arch_align_stack(x) (x)
extern unsigned long arch_align_stack(unsigned long sp);
/* Used in very early kernel initialization. */
extern unsigned long reloc_offset(void);

9
arch/powerpc/kernel/process.c
View file

@ -35,6 +35,8 @@
#include <linux/utsname.h>
#include <linux/ftrace.h>
#include <linux/kernel_stat.h>
#include <linux/personality.h>
#include <linux/random.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
@ -1138,3 +1140,10 @@ void thread_info_cache_init(void)
}
#endif /* THREAD_SHIFT < PAGE_SHIFT */
unsigned long arch_align_stack(unsigned long sp)
{
if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
sp -= get_random_int() & ~PAGE_MASK;
return sp & ~0xf;
}