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>

diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
index 38050b1..9c9b307 100644 (file)
--- a/arch/arm/include/asm/elf.h
+++ b/arch/arm/include/asm/elf.h
@@ -130,4 +130,8 @@ struct mm_struct;
 extern unsigned long arch_randomize_brk(struct mm_struct *mm);
 #define arch_randomize_brk arch_randomize_brk
 
+#define ARCH_HAS_SETUP_ADDITIONAL_PAGES 1
+struct linux_binprm;
+int arch_setup_additional_pages(struct linux_binprm *, int);
+
 #endif

diff --git a/arch/arm/include/asm/mmu.h b/arch/arm/include/asm/mmu.h
index e3d5554..7345e37 100644 (file)
--- a/arch/arm/include/asm/mmu.h
+++ b/arch/arm/include/asm/mmu.h
@@ -8,6 +8,7 @@ typedef struct {
        atomic64_t      id;
 #endif
        unsigned int    vmalloc_seq;
+       unsigned long   sigpage;
 } mm_context_t;
 
 #ifdef CONFIG_CPU_HAS_ASID

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index d3ca4f6..566d0d7 100644 (file)
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -428,8 +428,8 @@ unsigned long arch_randomize_brk(struct mm_struct *mm)
 #ifdef CONFIG_MMU
 /*
  * The vectors page is always readable from user space for the
- * atomic helpers and the signal restart code. Insert it into the
- * gate_vma so that it is visible through ptrace and /proc/<pid>/mem.
+ * atomic helpers. Insert it into the gate_vma so that it is visible
+ * through ptrace and /proc/<pid>/mem.
  */
 static struct vm_area_struct gate_vma = {
        .vm_start       = 0xffff0000,
@@ -461,6 +461,40 @@ int in_gate_area_no_mm(unsigned long addr)
 
 const char *arch_vma_name(struct vm_area_struct *vma)
 {
-       return (vma == &gate_vma) ? "[vectors]" : NULL;
+       return (vma == &gate_vma) ? "[vectors]" :
+               (vma->vm_mm && vma->vm_start == vma->vm_mm->context.sigpage) ?
+                "[sigpage]" : NULL;
+}
+
+extern struct page *get_signal_page(void);
+
+int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
+{
+       struct mm_struct *mm = current->mm;
+       struct page *page;
+       unsigned long addr;
+       int ret;
+
+       page = get_signal_page();
+       if (!page)
+               return -ENOMEM;
+
+       down_write(&mm->mmap_sem);
+       addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
+       if (IS_ERR_VALUE(addr)) {
+               ret = addr;
+               goto up_fail;
+       }
+
+       ret = install_special_mapping(mm, addr, PAGE_SIZE,
+               VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
+               &page);
+
+       if (ret == 0)
+               mm->context.sigpage = addr;
+
+ up_fail:
+       up_write(&mm->mmap_sem);
+       return ret;
 }
 #endif

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index 1c16c35..0f17e06 100644 (file)
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -8,6 +8,7 @@
  * published by the Free Software Foundation.
  */
 #include <linux/errno.h>
+#include <linux/random.h>
 #include <linux/signal.h>
 #include <linux/personality.h>
 #include <linux/uaccess.h>
@@ -15,12 +16,11 @@
 
 #include <asm/elf.h>
 #include <asm/cacheflush.h>
+#include <asm/traps.h>
 #include <asm/ucontext.h>
 #include <asm/unistd.h>
 #include <asm/vfp.h>
 
-#include "signal.h"
-
 /*
  * For ARM syscalls, we encode the syscall number into the instruction.
  */
@@ -40,11 +40,13 @@
 #define SWI_THUMB_SIGRETURN    (0xdf00 << 16 | 0x2700 | (__NR_sigreturn - __NR_SYSCALL_BASE))
 #define SWI_THUMB_RT_SIGRETURN (0xdf00 << 16 | 0x2700 | (__NR_rt_sigreturn - __NR_SYSCALL_BASE))
 
-const unsigned long sigreturn_codes[7] = {
+static const unsigned long sigreturn_codes[7] = {
        MOV_R7_NR_SIGRETURN,    SWI_SYS_SIGRETURN,    SWI_THUMB_SIGRETURN,
        MOV_R7_NR_RT_SIGRETURN, SWI_SYS_RT_SIGRETURN, SWI_THUMB_RT_SIGRETURN,
 };
 
+static unsigned long signal_return_offset;
+
 #ifdef CONFIG_CRUNCH
 static int preserve_crunch_context(struct crunch_sigframe __user *frame)
 {
@@ -401,12 +403,15 @@ setup_return(struct pt_regs *regs, struct ksignal *ksig,
                        return 1;
 
                if ((cpsr & MODE32_BIT) && !IS_ENABLED(CONFIG_ARM_MPU)) {
+                       struct mm_struct *mm = current->mm;
+
                        /*
-                        * 32-bit code can use the new high-page
-                        * signal return code support except when the MPU has
-                        * protected the vectors page from PL0
+                        * 32-bit code can use the signal return page
+                        * except when the MPU has protected the vectors
+                        * page from PL0
                         */
-                       retcode = KERN_SIGRETURN_CODE + (idx << 2) + thumb;
+                       retcode = mm->context.sigpage + signal_return_offset +
+                                 (idx << 2) + thumb;
                } else {
                        /*
                         * Ensure that the instruction cache sees
@@ -608,3 +613,36 @@ do_work_pending(struct pt_regs *regs, unsigned int thread_flags, int syscall)
        } while (thread_flags & _TIF_WORK_MASK);
        return 0;
 }
+
+static struct page *signal_page;
+
+struct page *get_signal_page(void)
+{
+       if (!signal_page) {
+               unsigned long ptr;
+               unsigned offset;
+               void *addr;
+
+               signal_page = alloc_pages(GFP_KERNEL, 0);
+
+               if (!signal_page)
+                       return NULL;
+
+               addr = page_address(signal_page);
+
+               /* Give the signal return code some randomness */
+               offset = 0x200 + (get_random_int() & 0x7fc);
+               signal_return_offset = offset;
+
+               /*
+                * Copy signal return handlers into the vector page, and
+                * set sigreturn to be a pointer to these.
+                */
+               memcpy(addr + offset, sigreturn_codes, sizeof(sigreturn_codes));
+
+               ptr = (unsigned long)addr + offset;
+               flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
+       }
+
+       return signal_page;
+}

diff --git a/arch/arm/kernel/signal.h b/arch/arm/kernel/signal.h
deleted file mode 100644 (file)
index 5ff067b..0000000
--- a/arch/arm/kernel/signal.h
+++ /dev/null
@@ -1,12 +0,0 @@
-/*
- *  linux/arch/arm/kernel/signal.h
- *
- *  Copyright (C) 2005-2009 Russell King.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
- */
-#define KERN_SIGRETURN_CODE    (CONFIG_VECTORS_BASE + 0x00000500)
-
-extern const unsigned long sigreturn_codes[7];

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index e3ca35c..ab517fc 100644 (file)
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -35,8 +35,6 @@
 #include <asm/tls.h>
 #include <asm/system_misc.h>
 
-#include "signal.h"
-
 static const char *handler[]= { "prefetch abort", "data abort", "address exception", "interrupt" };
 
 void *vectors_page;
@@ -850,13 +848,6 @@ void __init early_trap_init(void *vectors_base)
 
        kuser_init(vectors_base);
 
-       /*
-        * Copy signal return handlers into the vector page, and
-        * set sigreturn to be a pointer to these.
-        */
-       memcpy((void *)(vectors + KERN_SIGRETURN_CODE - CONFIG_VECTORS_BASE),
-              sigreturn_codes, sizeof(sigreturn_codes));
-
        flush_icache_range(vectors, vectors + PAGE_SIZE * 2);
        modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
 #else /* ifndef CONFIG_CPU_V7M */