From d839088caec6891a5070f0b1ce61031e458533a9 Mon Sep 17 00:00:00 2001
From: Anton Blanchard <anton@samba.org>
Date: Sun, 22 Feb 2009 01:50:03 +0000
Subject: 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>
---
 arch/powerpc/kernel/process.c | 9 +++++++++
 1 file changed, 9 insertions(+)

(limited to 'arch/powerpc/kernel/process.c')

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 8ede428..69b9d2d 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -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;
+}
-- 
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