ARM: move signal handlers into a vdso-like page
Move the signal handlers into a VDSO page rather than keeping them in the vectors page. This allows us to place them randomly within this page, and also map the page at a random location within userspace further protecting these code fragments from ROP attacks. The new VDSO page is also poisoned in the same way as the vector page. Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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@ -130,4 +130,8 @@ struct mm_struct;
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extern unsigned long arch_randomize_brk(struct mm_struct *mm);
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#define arch_randomize_brk arch_randomize_brk
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#define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
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struct linux_binprm;
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int arch_setup_additional_pages(struct linux_binprm *, int);
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#endif
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@ -8,6 +8,7 @@ typedef struct {
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atomic64_t id;
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#endif
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unsigned int vmalloc_seq;
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unsigned long sigpage;
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} mm_context_t;
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#ifdef CONFIG_CPU_HAS_ASID
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@ -428,8 +428,8 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
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#ifdef CONFIG_MMU
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/*
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* The vectors page is always readable from user space for the
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* atomic helpers and the signal restart code. Insert it into the
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* gate_vma so that it is visible through ptrace and /proc/<pid>/mem.
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* atomic helpers. Insert it into the gate_vma so that it is visible
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* through ptrace and /proc/<pid>/mem.
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*/
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static struct vm_area_struct gate_vma = {
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.vm_start = 0xffff0000,
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@ -461,6 +461,40 @@ int in_gate_area_no_mm(unsigned long addr)
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const char *arch_vma_name(struct vm_area_struct *vma)
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{
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return (vma == &gate_vma) ? "[vectors]" : NULL;
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return (vma == &gate_vma) ? "[vectors]" :
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(vma->vm_mm && vma->vm_start == vma->vm_mm->context.sigpage) ?
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"[sigpage]" : NULL;
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}
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extern struct page *get_signal_page(void);
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int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
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{
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struct mm_struct *mm = current->mm;
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struct page *page;
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unsigned long addr;
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int ret;
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page = get_signal_page();
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if (!page)
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return -ENOMEM;
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down_write(&mm->mmap_sem);
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addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
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if (IS_ERR_VALUE(addr)) {
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ret = addr;
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goto up_fail;
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}
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ret = install_special_mapping(mm, addr, PAGE_SIZE,
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VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
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&page);
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if (ret == 0)
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mm->context.sigpage = addr;
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up_fail:
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up_write(&mm->mmap_sem);
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return ret;
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}
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#endif
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@ -8,6 +8,7 @@
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* published by the Free Software Foundation.
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*/
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#include <linux/errno.h>
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#include <linux/random.h>
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#include <linux/signal.h>
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#include <linux/personality.h>
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#include <linux/uaccess.h>
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@ -15,12 +16,11 @@
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#include <asm/elf.h>
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#include <asm/cacheflush.h>
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#include <asm/traps.h>
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#include <asm/ucontext.h>
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#include <asm/unistd.h>
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#include <asm/vfp.h>
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#include "signal.h"
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/*
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* For ARM syscalls, we encode the syscall number into the instruction.
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*/
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@ -40,11 +40,13 @@
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#define SWI_THUMB_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_sigreturn - __NR_SYSCALL_BASE))
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#define SWI_THUMB_RT_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
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const unsigned long sigreturn_codes[7] = {
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static const unsigned long sigreturn_codes[7] = {
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MOV_R7_NR_SIGRETURN, SWI_SYS_SIGRETURN, SWI_THUMB_SIGRETURN,
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MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
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};
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static unsigned long signal_return_offset;
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#ifdef CONFIG_CRUNCH
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static int preserve_crunch_context(struct crunch_sigframe __user *frame)
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{
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@ -401,12 +403,15 @@ setup_return(struct pt_regs *regs, struct ksignal *ksig,
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return 1;
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if ((cpsr & MODE32_BIT) && !IS_ENABLED(CONFIG_ARM_MPU)) {
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struct mm_struct *mm = current->mm;
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/*
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* 32-bit code can use the new high-page
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* signal return code support except when the MPU has
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* protected the vectors page from PL0
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* 32-bit code can use the signal return page
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* except when the MPU has protected the vectors
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* page from PL0
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*/
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retcode = KERN_SIGRETURN_CODE + (idx << 2) + thumb;
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retcode = mm->context.sigpage + signal_return_offset +
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(idx << 2) + thumb;
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} else {
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/*
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* Ensure that the instruction cache sees
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@ -608,3 +613,36 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
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} while (thread_flags & _TIF_WORK_MASK);
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return 0;
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}
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static struct page *signal_page;
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struct page *get_signal_page(void)
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{
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if (!signal_page) {
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unsigned long ptr;
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unsigned offset;
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void *addr;
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signal_page = alloc_pages(GFP_KERNEL, 0);
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if (!signal_page)
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return NULL;
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addr = page_address(signal_page);
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/* Give the signal return code some randomness */
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offset = 0x200 + (get_random_int() & 0x7fc);
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signal_return_offset = offset;
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/*
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* Copy signal return handlers into the vector page, and
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* set sigreturn to be a pointer to these.
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*/
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memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
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ptr = (unsigned long)addr + offset;
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flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
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}
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return signal_page;
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}
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@ -1,12 +0,0 @@
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/*
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* linux/arch/arm/kernel/signal.h
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*
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* Copyright (C) 2005-2009 Russell King.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#define KERN_SIGRETURN_CODE (CONFIG_VECTORS_BASE + 0x00000500)
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extern const unsigned long sigreturn_codes[7];
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@ -35,8 +35,6 @@
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#include <asm/tls.h>
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#include <asm/system_misc.h>
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#include "signal.h"
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static const char *handler[]= { "prefetch abort", "data abort", "address exception", "interrupt" };
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void *vectors_page;
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@ -850,13 +848,6 @@ void __init early_trap_init(void *vectors_base)
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kuser_init(vectors_base);
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/*
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* Copy signal return handlers into the vector page, and
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* set sigreturn to be a pointer to these.
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*/
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memcpy((void *)(vectors + KERN_SIGRETURN_CODE - CONFIG_VECTORS_BASE),
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sigreturn_codes, sizeof(sigreturn_codes));
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flush_icache_range(vectors, vectors + PAGE_SIZE * 2);
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modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
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#else /* ifndef CONFIG_CPU_V7M */
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