From: Arjan van de Ven <arjan@infradead.org>
The patch below randomizes the starting point of the mmap area.
This has the effect that all non-prelinked shared libaries and all bigger
malloc()s will be randomized between various invocations of the binary.
Prelinked binaries get a address-hint from ld.so in their mmap and are thus
exempt from this randomisation, in order to not break the prelink advantage.
The randomisation range is 1 megabyte (this is bigger than the stack
randomisation since the stack randomisation only needs 16 bytes alignment
while the mmap needs page alignment, a 64kb range would not have given enough
entropy to be effective)
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/arch/i386/mm/mmap.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletion(-)
diff -puN arch/i386/mm/mmap.c~randomisation-mmap-randomisation arch/i386/mm/mmap.c
--- 25/arch/i386/mm/mmap.c~randomisation-mmap-randomisation 2005-02-02 15:22:18.115160840 -0800
+++ 25-akpm/arch/i386/mm/mmap.c 2005-02-02 15:22:18.118160384 -0800
@@ -26,6 +26,7 @@
#include <linux/personality.h>
#include <linux/mm.h>
+#include <linux/random.h>
/*
* Top of mmap area (just below the process stack).
@@ -38,13 +39,17 @@
static inline unsigned long mmap_base(struct mm_struct *mm)
{
unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
+ unsigned long random_factor = 0;
+
+ if (current->flags & PF_RANDOMIZE)
+ random_factor = get_random_int() % (1024*1024);
if (gap < MIN_GAP)
gap = MIN_GAP;
else if (gap > MAX_GAP)
gap = MAX_GAP;
- return TASK_SIZE - (gap & PAGE_MASK);
+ return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
}
/*
_