[PATCH] vdso: randomize the i386 vDSO by moving it into a vma

Move the i386 VDSO down into a vma and thus randomize it.

Besides the security implications, this feature also helps debuggers, which
can COW a vma-backed VDSO just like a normal DSO and can thus do
single-stepping and other debugging features.

It's good for hypervisors (Xen, VMWare) too, which typically live in the same
high-mapped address space as the VDSO, hence whenever the VDSO is used, they
get lots of guest pagefaults and have to fix such guest accesses up - which
slows things down instead of speeding things up (the primary purpose of the
VDSO).

There's a new CONFIG_COMPAT_VDSO (default=y) option, which provides support
for older glibcs that still rely on a prelinked high-mapped VDSO.  Newer
distributions (using glibc 2.3.3 or later) can turn this option off.  Turning
it off is also recommended for security reasons: attackers cannot use the
predictable high-mapped VDSO page as syscall trampoline anymore.

There is a new vdso=[0|1] boot option as well, and a runtime
/proc/sys/vm/vdso_enabled sysctl switch, that allows the VDSO to be turned
on/off.

(This version of the VDSO-randomization patch also has working ELF
coredumping, the previous patch crashed in the coredumping code.)

This code is a combined work of the exec-shield VDSO randomization
code and Gerd Hoffmann's hypervisor-centric VDSO patch. Rusty Russell
started this patch and i completed it.

[akpm@osdl.org: cleanups]
[akpm@osdl.org: compile fix]
[akpm@osdl.org: compile fix 2]
[akpm@osdl.org: compile fix 3]
[akpm@osdl.org: revernt MAXMEM change]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Cc: Gerd Hoffmann <kraxel@suse.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Zachary Amsden <zach@vmware.com>
Cc: Andi Kleen <ak@muc.de>
Cc: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

6 files changed, 139 insertions, 12 deletions

diff --git a/arch/i386/kernel/asm-offsets.c b/arch/i386/kernel/asm-offsets.c
index 1c3a809e6421..c80271f8f084 100644
--- a/arch/i386/kernel/asm-offsets.c
+++ b/arch/i386/kernel/asm-offsets.c
@@ -14,6 +14,7 @@
 #include <asm/fixmap.h>
 #include <asm/processor.h>
 #include <asm/thread_info.h>
+#include <asm/elf.h>
 
 #define DEFINE(sym, val) \
         asm volatile("\n->" #sym " %0 " #val : : "i" (val))
@@ -54,6 +55,7 @@ void foo(void)
         OFFSET(TI_preempt_count, thread_info, preempt_count);
         OFFSET(TI_addr_limit, thread_info, addr_limit);
         OFFSET(TI_restart_block, thread_info, restart_block);
+        OFFSET(TI_sysenter_return, thread_info, sysenter_return);
         BLANK();
 
         OFFSET(EXEC_DOMAIN_handler, exec_domain, handler);
@@ -69,7 +71,7 @@ void foo(void)
                  sizeof(struct tss_struct));
 
         DEFINE(PAGE_SIZE_asm, PAGE_SIZE);
-        DEFINE(VSYSCALL_BASE, __fix_to_virt(FIX_VSYSCALL));
+        DEFINE(VDSO_PRELINK, VDSO_PRELINK);
 
         OFFSET(crypto_tfm_ctx_offset, crypto_tfm, __crt_ctx);
 }
diff --git a/arch/i386/kernel/entry.S b/arch/i386/kernel/entry.S
index e8d2630fd19a..fbdb933251b6 100644
--- a/arch/i386/kernel/entry.S
+++ b/arch/i386/kernel/entry.S
@@ -270,7 +270,12 @@ sysenter_past_esp:
         pushl $(__USER_CS)
         CFI_ADJUST_CFA_OFFSET 4
         /*CFI_REL_OFFSET cs, 0*/
-        pushl $SYSENTER_RETURN
+        /*
+         * Push current_thread_info()->sysenter_return to the stack.
+         * A tiny bit of offset fixup is necessary - 4*4 means the 4 words
+         * pushed above; +8 corresponds to copy_thread's esp0 setting.
+         */
+        pushl (TI_sysenter_return-THREAD_SIZE+8+4*4)(%esp)
         CFI_ADJUST_CFA_OFFSET 4
         CFI_REL_OFFSET eip, 0
 
diff --git a/arch/i386/kernel/signal.c b/arch/i386/kernel/signal.c
index 5c352c3a9e7f..43002cfb40c4 100644
--- a/arch/i386/kernel/signal.c
+++ b/arch/i386/kernel/signal.c
@@ -351,7 +351,7 @@ static int setup_frame(int sig, struct k_sigaction *ka,
                         goto give_sigsegv;
         }
 
-        restorer = &__kernel_sigreturn;
+        restorer = (void *)VDSO_SYM(&__kernel_sigreturn);
         if (ka->sa.sa_flags & SA_RESTORER)
                 restorer = ka->sa.sa_restorer;
 
@@ -447,7 +447,7 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
                 goto give_sigsegv;
 
         /* Set up to return from userspace.  */
-        restorer = &__kernel_rt_sigreturn;
+        restorer = (void *)VDSO_SYM(&__kernel_rt_sigreturn);
         if (ka->sa.sa_flags & SA_RESTORER)
                 restorer = ka->sa.sa_restorer;
         err |= __put_user(restorer, &frame->pretcode);
diff --git a/arch/i386/kernel/sysenter.c b/arch/i386/kernel/sysenter.c
index 0bada1870bdf..c60419dee018 100644
--- a/arch/i386/kernel/sysenter.c
+++ b/arch/i386/kernel/sysenter.c
@@ -2,6 +2,8 @@
  * linux/arch/i386/kernel/sysenter.c
  *
  * (C) Copyright 2002 Linus Torvalds
+ * Portions based on the vdso-randomization code from exec-shield:
+ * Copyright(C) 2005-2006, Red Hat, Inc., Ingo Molnar
  *
  * This file contains the needed initializations to support sysenter.
  */
@@ -13,12 +15,31 @@
 #include <linux/gfp.h>
 #include <linux/string.h>
 #include <linux/elf.h>
+#include <linux/mm.h>
+#include <linux/module.h>
 
 #include <asm/cpufeature.h>
 #include <asm/msr.h>
 #include <asm/pgtable.h>
 #include <asm/unistd.h>
 
+/*
+ * Should the kernel map a VDSO page into processes and pass its
+ * address down to glibc upon exec()?
+ */
+unsigned int __read_mostly vdso_enabled = 1;
+
+EXPORT_SYMBOL_GPL(vdso_enabled);
+
+static int __init vdso_setup(char *s)
+{
+        vdso_enabled = simple_strtoul(s, NULL, 0);
+
+        return 1;
+}
+
+__setup("vdso=", vdso_setup);
+
 extern asmlinkage void sysenter_entry(void);
 
 void enable_sep_cpu(void)
@@ -45,23 +66,122 @@ void enable_sep_cpu(void)
  */
 extern const char vsyscall_int80_start, vsyscall_int80_end;
 extern const char vsyscall_sysenter_start, vsyscall_sysenter_end;
+static void *syscall_page;
 
 int __init sysenter_setup(void)
 {
-        void *page = (void *)get_zeroed_page(GFP_ATOMIC);
+        syscall_page = (void *)get_zeroed_page(GFP_ATOMIC);
 
-        __set_fixmap(FIX_VSYSCALL, __pa(page), PAGE_READONLY_EXEC);
+#ifdef CONFIG_COMPAT_VDSO
+        __set_fixmap(FIX_VDSO, __pa(syscall_page), PAGE_READONLY);
+        printk("Compat vDSO mapped to %08lx.\n", __fix_to_virt(FIX_VDSO));
+#else
+        /*
+         * In the non-compat case the ELF coredumping code needs the fixmap:
+         */
+        __set_fixmap(FIX_VDSO, __pa(syscall_page), PAGE_KERNEL_RO);
+#endif
 
         if (!boot_cpu_has(X86_FEATURE_SEP)) {
-                memcpy(page,
+                memcpy(syscall_page,
                        &vsyscall_int80_start,
                        &vsyscall_int80_end - &vsyscall_int80_start);
                 return 0;
         }
 
-        memcpy(page,
+        memcpy(syscall_page,
                &vsyscall_sysenter_start,
                &vsyscall_sysenter_end - &vsyscall_sysenter_start);
 
         return 0;
 }
+
+static struct page *syscall_nopage(struct vm_area_struct *vma,
+                                unsigned long adr, int *type)
+{
+        struct page *p = virt_to_page(adr - vma->vm_start + syscall_page);
+        get_page(p);
+        return p;
+}
+
+/* Prevent VMA merging */
+static void syscall_vma_close(struct vm_area_struct *vma)
+{
+}
+
+static struct vm_operations_struct syscall_vm_ops = {
+        .close = syscall_vma_close,
+        .nopage = syscall_nopage,
+};
+
+/* Defined in vsyscall-sysenter.S */
+extern void SYSENTER_RETURN;
+
+/* Setup a VMA at program startup for the vsyscall page */
+int arch_setup_additional_pages(struct linux_binprm *bprm, int exstack)
+{
+        struct vm_area_struct *vma;
+        struct mm_struct *mm = current->mm;
+        unsigned long addr;
+        int ret;
+
+        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;
+        }
+
+        vma = kmem_cache_zalloc(vm_area_cachep, SLAB_KERNEL);
+        if (!vma) {
+                ret = -ENOMEM;
+                goto up_fail;
+        }
+
+        vma->vm_start = addr;
+        vma->vm_end = addr + PAGE_SIZE;
+        /* MAYWRITE to allow gdb to COW and set breakpoints */
+        vma->vm_flags = VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYEXEC|VM_MAYWRITE;
+        vma->vm_flags |= mm->def_flags;
+        vma->vm_page_prot = protection_map[vma->vm_flags & 7];
+        vma->vm_ops = &syscall_vm_ops;
+        vma->vm_mm = mm;
+
+        ret = insert_vm_struct(mm, vma);
+        if (ret)
+                goto free_vma;
+
+        current->mm->context.vdso = (void *)addr;
+        current_thread_info()->sysenter_return =
+                                    (void *)VDSO_SYM(&SYSENTER_RETURN);
+        mm->total_vm++;
+up_fail:
+        up_write(&mm->mmap_sem);
+        return ret;
+
+free_vma:
+        kmem_cache_free(vm_area_cachep, vma);
+        return ret;
+}
+
+const char *arch_vma_name(struct vm_area_struct *vma)
+{
+        if (vma->vm_mm && vma->vm_start == (long)vma->vm_mm->context.vdso)
+                return "[vdso]";
+        return NULL;
+}
+
+struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
+{
+        return NULL;
+}
+
+int in_gate_area(struct task_struct *task, unsigned long addr)
+{
+        return 0;
+}
+
+int in_gate_area_no_task(unsigned long addr)
+{
+        return 0;
+}
diff --git a/arch/i386/kernel/vsyscall-sysenter.S b/arch/i386/kernel/vsyscall-sysenter.S
index 3b62baa6a371..1a36d26e15eb 100644
--- a/arch/i386/kernel/vsyscall-sysenter.S
+++ b/arch/i386/kernel/vsyscall-sysenter.S
@@ -42,10 +42,10 @@ __kernel_vsyscall:
         /* 7: align return point with nop's to make disassembly easier */
         .space 7,0x90
 
-        /* 14: System call restart point is here! (SYSENTER_RETURN - 2) */
+        /* 14: System call restart point is here! (SYSENTER_RETURN-2) */
         jmp .Lenter_kernel
         /* 16: System call normal return point is here! */
-        .globl SYSENTER_RETURN  /* Symbol used by entry.S.  */
+        .globl SYSENTER_RETURN  /* Symbol used by sysenter.c  */
 SYSENTER_RETURN:
         pop %ebp
 .Lpop_ebp:
diff --git a/arch/i386/kernel/vsyscall.lds.S b/arch/i386/kernel/vsyscall.lds.S
index 98699ca6e52d..e26975fc68b6 100644
--- a/arch/i386/kernel/vsyscall.lds.S
+++ b/arch/i386/kernel/vsyscall.lds.S
@@ -7,7 +7,7 @@
 
 SECTIONS
 {
-  . = VSYSCALL_BASE + SIZEOF_HEADERS;
+  . = VDSO_PRELINK + SIZEOF_HEADERS;
 
   .hash           : { *(.hash) }                :text
   .dynsym         : { *(.dynsym) }
@@ -20,7 +20,7 @@ SECTIONS
      For the layouts to match, we need to skip more than enough
      space for the dynamic symbol table et al.  If this amount
      is insufficient, ld -shared will barf.  Just increase it here.  */
-  . = VSYSCALL_BASE + 0x400;
+  . = VDSO_PRELINK + 0x400;
 
   .text           : { *(.text) }                :text =0x90909090
   .note           : { *(.note.*) }              :text :note