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Commit d839088c authored by Anton Blanchard's avatar Anton Blanchard Committed by Benjamin Herrenschmidt
Browse files

powerpc: Randomise lower bits of stack address 



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);
}

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after:
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Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent 2dadb987

arch/powerpc/include/asm/system.h

+1 −1
Original line number Diff line number Diff line
@@ -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);

arch/powerpc/kernel/process.c

+9 −0
Original line number Diff line number Diff line
@@ -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;

}