[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>

1 files changed, 40 insertions, 13 deletions

diff --git a/include/asm-i386/elf.h b/include/asm-i386/elf.h
index 4153d80e4d2b..1eac92cb5b16 100644
--- a/include/asm-i386/elf.h
+++ b/include/asm-i386/elf.h
@@ -10,6 +10,7 @@
 #include <asm/processor.h>
 #include <asm/system.h>         /* for savesegment */
 #include <asm/auxvec.h>
+#include <asm/desc.h>
 
 #include <linux/utsname.h>
 
@@ -129,15 +130,41 @@ extern int dump_task_extended_fpu (struct task_struct *, struct user_fxsr_struct
 #define ELF_CORE_COPY_FPREGS(tsk, elf_fpregs) dump_task_fpu(tsk, elf_fpregs)
 #define ELF_CORE_COPY_XFPREGS(tsk, elf_xfpregs) dump_task_extended_fpu(tsk, elf_xfpregs)
 
-#define VSYSCALL_BASE   (__fix_to_virt(FIX_VSYSCALL))
-#define VSYSCALL_EHDR   ((const struct elfhdr *) VSYSCALL_BASE)
-#define VSYSCALL_ENTRY  ((unsigned long) &__kernel_vsyscall)
+#define VDSO_HIGH_BASE          (__fix_to_virt(FIX_VDSO))
+#define VDSO_BASE               ((unsigned long)current->mm->context.vdso)
+
+#ifdef CONFIG_COMPAT_VDSO
+# define VDSO_COMPAT_BASE       VDSO_HIGH_BASE
+# define VDSO_PRELINK           VDSO_HIGH_BASE
+#else
+# define VDSO_COMPAT_BASE       VDSO_BASE
+# define VDSO_PRELINK           0
+#endif
+
+#define VDSO_COMPAT_SYM(x) \
+                (VDSO_COMPAT_BASE + (unsigned long)(x) - VDSO_PRELINK)
+
+#define VDSO_SYM(x) \
+                (VDSO_BASE + (unsigned long)(x) - VDSO_PRELINK)
+
+#define VDSO_HIGH_EHDR          ((const struct elfhdr *) VDSO_HIGH_BASE)
+#define VDSO_EHDR               ((const struct elfhdr *) VDSO_COMPAT_BASE)
+
 extern void __kernel_vsyscall;
 
+#define VDSO_ENTRY              VDSO_SYM(&__kernel_vsyscall)
+
+#define ARCH_HAS_SETUP_ADDITIONAL_PAGES
+struct linux_binprm;
+extern int arch_setup_additional_pages(struct linux_binprm *bprm,
+                                       int executable_stack);
+
+extern unsigned int vdso_enabled;
+
 #define ARCH_DLINFO                                             \
-do {                                                            \
-                NEW_AUX_ENT(AT_SYSINFO, VSYSCALL_ENTRY);        \
-                NEW_AUX_ENT(AT_SYSINFO_EHDR, VSYSCALL_BASE);    \
+do if (vdso_enabled) {                                          \
+                NEW_AUX_ENT(AT_SYSINFO, VDSO_ENTRY);            \
+                NEW_AUX_ENT(AT_SYSINFO_EHDR, VDSO_COMPAT_BASE); \
 } while (0)
 
 /*
@@ -148,15 +175,15 @@ do {								\
  * Dumping its extra ELF program headers includes all the other information
  * a debugger needs to easily find how the vsyscall DSO was being used.
  */
-#define ELF_CORE_EXTRA_PHDRS            (VSYSCALL_EHDR->e_phnum)
+#define ELF_CORE_EXTRA_PHDRS            (VDSO_HIGH_EHDR->e_phnum)
 #define ELF_CORE_WRITE_EXTRA_PHDRS                                            \
 do {                                                                          \
         const struct elf_phdr *const vsyscall_phdrs =                         \
-                (const struct elf_phdr *) (VSYSCALL_BASE                      \
-                                           + VSYSCALL_EHDR->e_phoff);         \
+                (const struct elf_phdr *) (VDSO_HIGH_BASE                     \
+                                           + VDSO_HIGH_EHDR->e_phoff);    \
         int i;                                                                \
         Elf32_Off ofs = 0;                                                    \
-        for (i = 0; i < VSYSCALL_EHDR->e_phnum; ++i) {                        \
+        for (i = 0; i < VDSO_HIGH_EHDR->e_phnum; ++i) {               \
                 struct elf_phdr phdr = vsyscall_phdrs[i];                     \
                 if (phdr.p_type == PT_LOAD) {                                 \
                         BUG_ON(ofs != 0);                                     \
@@ -174,10 +201,10 @@ do {									      \
 #define ELF_CORE_WRITE_EXTRA_DATA                                             \
 do {                                                                          \
         const struct elf_phdr *const vsyscall_phdrs =                         \
-                (const struct elf_phdr *) (VSYSCALL_BASE                      \
-                                           + VSYSCALL_EHDR->e_phoff);         \
+                (const struct elf_phdr *) (VDSO_HIGH_BASE                     \
+                                           + VDSO_HIGH_EHDR->e_phoff);    \
         int i;                                                                \
-        for (i = 0; i < VSYSCALL_EHDR->e_phnum; ++i) {                        \
+        for (i = 0; i < VDSO_HIGH_EHDR->e_phnum; ++i) {               \
                 if (vsyscall_phdrs[i].p_type == PT_LOAD)                      \
                         DUMP_WRITE((void *) vsyscall_phdrs[i].p_vaddr,        \
                                    PAGE_ALIGN(vsyscall_phdrs[i].p_memsz));    \