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Commit 913bd906 authored by Andi Kleen's avatar Andi Kleen Committed by Linus Torvalds
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[PATCH] x86_64: Increase the variability of the process stack on 64bit architectures 



8MB is not really very random, use 1GB (or more with larger page sizes)
instead.

Also use the low bits of the random generator output now instead of
throwing them away.

Only enabled on x86-64 right now. Other architectures need to add
a suitable STACK_RND_MASK

Cc: mingo@elte.hu
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent dca99a38

fs/binfmt_elf.c

+9 −4
Original line number Diff line number Diff line
@@ -500,17 +500,22 @@ static unsigned long load_aout_interp(struct exec * interp_ex, 
#define INTERPRETER_AOUT 1

#define INTERPRETER_ELF 2



#ifndef STACK_RND_MASK

#define STACK_RND_MASK 0x7ff		/* with 4K pages 8MB of VA */

#endif



static unsigned long randomize_stack_top(unsigned long stack_top)

{

	unsigned int random_variable = 0;



	if (current->flags & PF_RANDOMIZE)

		random_variable = get_random_int() % (8*1024*1024);

	if (current->flags & PF_RANDOMIZE) {

		random_variable = get_random_int() & STACK_RND_MASK;

		random_variable <<= PAGE_SHIFT;

	}

#ifdef CONFIG_STACK_GROWSUP

	return PAGE_ALIGN(stack_top + random_variable);

	return PAGE_ALIGN(stack_top) + random_variable;

#else

	return PAGE_ALIGN(stack_top - random_variable);

	return PAGE_ALIGN(stack_top) - random_variable;

#endif

}

include/asm-x86_64/elf.h

+4 −0
Original line number Diff line number Diff line
@@ -8,6 +8,7 @@ 
#include <asm/ptrace.h>

#include <asm/user.h>

#include <asm/processor.h>

#include <asm/compat.h>



/* x86-64 relocation types */

#define R_X86_64_NONE		0	/* No reloc */
@@ -157,6 +158,9 @@ extern int dump_task_fpu (struct task_struct *, elf_fpregset_t *); 
#define ELF_CORE_COPY_TASK_REGS(tsk, elf_regs) dump_task_regs(tsk, elf_regs)

#define ELF_CORE_COPY_FPREGS(tsk, elf_fpregs) dump_task_fpu(tsk, elf_fpregs)



/* 1GB for 64bit, 8MB for 32bit */

#define STACK_RND_MASK (is_compat_task() ? 0x7ff : 0x3fffff)



#endif



#endif