[PATCH] i386 and x86_64: randomize brk()

[Jiri Kosina]

From: Jiri Kosina <jkosina@xxxxxxx>

i386 and x86_64: randomize brk()

This patch randomizes the location of the heap (brk) for i386 and x86_64. 
The range is randomized in the range starting at current brk location up 
to 0x02000000 offset on both architectures. This, together with 
pie-executable-randomization.patch and 
pie-executable-randomization-fix.patch, should make the address space 
randomization on i386 and x86_64 complete (modulo vDSO randomization).

The code is based on execshield code written by Ingo Molnar.

Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Jakub Jelinek <jakub@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxx>
Cc: Kees Cook <kees@xxxxxxxxxxx>
Cc: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Signed-off-by: Jiri Kosina <jkosina@xxxxxxx>

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 8466471..21edde5 100644
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -949,3 +949,15 @@ unsigned long arch_align_stack(unsigned long sp)
 		sp -= get_random_int() % 8192;
 	return sp & ~0xf;
 }
+
+void arch_randomize_brk(void)
+{
+	unsigned long new_brk, range_start, range_end;
+
+	range_start = current->mm->brk;
+	range_end = range_start + 0x02000000;
+	new_brk = randomize_range(range_start, range_end, 0);
+	if (new_brk)
+		current->mm->brk = current->mm->start_brk = new_brk;
+}
+
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index 2842f50..37613f3 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -902,3 +902,15 @@ unsigned long arch_align_stack(unsigned long sp)
 		sp -= get_random_int() % 8192;
 	return sp & ~0xf;
 }
+
+void arch_randomize_brk(void)
+{
+	unsigned long new_brk, range_start, range_end;
+
+	range_start = current->mm->brk;
+	range_end = range_start + 0x02000000;
+	new_brk = randomize_range(range_start, range_end, 0);
+	if (new_brk)
+		current->mm->brk = current->mm->start_brk = new_brk;
+}
+
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index d65f1d9..790b09e 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1073,6 +1073,11 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
 	current->mm->end_data = end_data;
 	current->mm->start_stack = bprm->p;
 
+#ifdef ARCH_HAS_RANDOMIZE_BRK
+	if (current->flags & PF_RANDOMIZE)
+		arch_randomize_brk();
+#endif
+
 	if (current->personality & MMAP_PAGE_ZERO) {
 		/* Why this, you ask???  Well SVr4 maps page 0 as read-only,
 		   and some applications "depend" upon this behavior.
diff --git a/include/asm-i386/elf.h b/include/asm-i386/elf.h
index b32df3a..34752bc 100644
--- a/include/asm-i386/elf.h
+++ b/include/asm-i386/elf.h
@@ -160,4 +160,7 @@ do if (vdso_enabled) {							\
 
 #endif
 
+#define ARCH_HAS_RANDOMIZE_BRK
+extern void arch_randomize_brk(void);
+
 #endif
diff --git a/include/asm-x86_64/elf.h b/include/asm-x86_64/elf.h
index b4fbe47..ec56e67 100644
--- a/include/asm-x86_64/elf.h
+++ b/include/asm-x86_64/elf.h
@@ -177,4 +177,7 @@ do if (vdso_enabled) {						\
 
 #endif
 
+#define ARCH_HAS_RANDOMIZE_BRK
+extern void arch_randomize_brk(void);
+
 #endif
-
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