From 913bd906019514579b3c7ec5ab9c463e89207a57 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Sat, 25 Mar 2006 16:29:09 +0100 Subject: [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: Andi Kleen Signed-off-by: Linus Torvalds --- fs/binfmt_elf.c | 13 +++++++++---- include/asm-x86_64/elf.h | 4 ++++ 2 files changed, 13 insertions(+), 4 deletions(-) diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 4349113881fbf..537893a16014c 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -500,17 +500,22 @@ out: #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 } diff --git a/include/asm-x86_64/elf.h b/include/asm-x86_64/elf.h index 43862cd6a569d..c98633af07d26 100644 --- a/include/asm-x86_64/elf.h +++ b/include/asm-x86_64/elf.h @@ -8,6 +8,7 @@ #include #include #include +#include /* 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 -- cgit 1.2.3-korg