[S390] mmap: consider stack address randomization

Consider stack address randomization when calulating mmap_base for
flexible mmap layout . Because of address randomization the stack
address can be up to 8MB lower than STACK_TOP.
When calculating mmap_base this isn't taken into account, which could
lead to the case that the gap between the real stack top and mmap_base
is lower than what ulimit specifies for the maximum stack size.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 12 insertions, 1 deletions

diff --git a/arch/s390/include/asm/elf.h b/arch/s390/include/asm/elf.h
index 354d42616c7e..9dbd3e7a3bc3 100644
--- a/arch/s390/include/asm/elf.h
+++ b/arch/s390/include/asm/elf.h
@@ -206,6 +206,8 @@ do {								\
         current->mm->context.noexec == 0;               \
 })
 
+#define STACK_RND_MASK  0x7ffUL
+
 #define ARCH_DLINFO                                                         \
 do {                                                                        \
         if (vdso_enabled)                                                   \
diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 869efbaed3ea..5578740ab9c9 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -30,6 +30,15 @@
 #include <asm/pgalloc.h>
 #include <asm/compat.h>
 
+static unsigned long stack_maxrandom_size(void)
+{
+        if (!(current->flags & PF_RANDOMIZE))
+                return 0;
+        if (current->personality & ADDR_NO_RANDOMIZE)
+                return 0;
+        return STACK_RND_MASK << PAGE_SHIFT;
+}
+
 /*
  * Top of mmap area (just below the process stack).
  *
@@ -47,7 +56,7 @@ static inline unsigned long mmap_base(void)
         else if (gap > MAX_GAP)
                 gap = MAX_GAP;
 
-        return STACK_TOP - (gap & PAGE_MASK);
+        return STACK_TOP - stack_maxrandom_size() - (gap & PAGE_MASK);
 }
 
 static inline int mmap_is_legacy(void)