x86: Increase MIN_GAP to include randomized stack

[ trivial backport to 2.6.27: Chuck Ebbert <cebbert@redhat.com> ]

commit 80938332d8cf652f6b16e0788cf0ca136befe0b5 upstream.

Currently we are not including randomized stack size when calculating
mmap_base address in arch_pick_mmap_layout for topdown case. This might
cause that mmap_base starts in the stack reserved area because stack is
randomized by 1GB for 64b (8MB for 32b) and the minimum gap is 128MB.

If the stack really grows down to mmap_base then we can get silent mmap
region overwrite by the stack values.

Let's include maximum stack randomization size into MIN_GAP which is
used as the low bound for the gap in mmap.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
LKML-Reference: <1252400515-6866-1-git-send-email-mhocko@suse.cz>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Chuck Ebbert <cebbert@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
index 56fe7124fbec932c0b14f8d9dbe9b448fcdd88b7..47dd8f55028bc31eace5b5f7be2cdebcdb7577a3 100644 (file)
--- a/arch/x86/mm/mmap.c
+++ b/arch/x86/mm/mmap.c
@@ -29,13 +29,26 @@
 #include <linux/random.h>
 #include <linux/limits.h>
 #include <linux/sched.h>
+#include <asm/elf.h>
+
+static unsigned int stack_maxrandom_size(void)
+{
+       unsigned int max = 0;
+       if ((current->flags & PF_RANDOMIZE) &&
+               !(current->personality & ADDR_NO_RANDOMIZE)) {
+               max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
+       }
+
+       return max;
+}
+
 
 /*
  * Top of mmap area (just below the process stack).
  *
- * Leave an at least ~128 MB hole.
+ * Leave an at least ~128 MB hole with possible stack randomization.
  */
-#define MIN_GAP (128*1024*1024)
+#define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
 #define MAX_GAP (TASK_SIZE/6*5)
 
 /*

diff --git a/include/asm-x86/elf.h b/include/asm-x86/elf.h
index 7be4733c793e58c404fbab54d3c34e2e05ff8aa0..36343b6935d5c776026e9a34735c93a38b69d1cd 100644 (file)
--- a/include/asm-x86/elf.h
+++ b/include/asm-x86/elf.h
@@ -287,6 +287,8 @@ do {                                                                        \
 
 #ifdef CONFIG_X86_32
 
+#define STACK_RND_MASK (0x7ff)
+
 #define VDSO_HIGH_BASE         (__fix_to_virt(FIX_VDSO))
 
 #define ARCH_DLINFO            ARCH_DLINFO_IA32(vdso_enabled)