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 <[email protected]>
---
Index: linux-2.6/arch/powerpc/include/asm/system.h
===================================================================
--- linux-2.6.orig/arch/powerpc/include/asm/system.h 2009-02-20
13:39:05.000000000 +1100
+++ linux-2.6/arch/powerpc/include/asm/system.h 2009-02-20 13:51:39.000000000
+1100
@@ -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);
Index: linux-2.6/arch/powerpc/kernel/process.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/process.c 2009-02-20
13:39:05.000000000 +1100
+++ linux-2.6/arch/powerpc/kernel/process.c 2009-02-20 13:51:39.000000000
+1100
@@ -34,6 +34,8 @@
#include <linux/hardirq.h>
#include <linux/utsname.h>
#include <linux/kernel_stat.h>
+#include <linux/personality.h>
+#include <linux/random.h>
#include <asm/pgtable.h>
#include <asm/uaccess.h>
@@ -1122,3 +1124,10 @@
}
#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;
+}
--
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