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);
}
before:
80
80
80
80
80
after:
610
490
300
6b0
d80
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/include/asm/system.h b/arch/powerpc/include/asm/system.h
index 2a4be19..f612798 100644
--- a/arch/powerpc/include/asm/system.h
+++ b/arch/powerpc/include/asm/system.h
@@ -531,7 +531,7 @@
#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);