x86-64: Fill unused parts of the vsyscall page with 0xcc

Jumping to 0x00 might do something depending on the following
bytes. Jumping to 0xcc is a trap.  So fill the unused parts of
the vsyscall page with 0xcc to make it useless for exploits to
jump there.

Signed-off-by: Andy Lutomirski <luto@mit.edu>
Cc: Jesper Juhl <jj@chaosbits.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Jan Beulich <JBeulich@novell.com>
Cc: richard -rw- weinberger <richard.weinberger@gmail.com>
Cc: Mikael Pettersson <mikpe@it.uu.se>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Louis Rilling <Louis.Rilling@kerlabs.com>
Cc: Valdis.Kletnieks@vt.edu
Cc: pageexec@freemail.hu
Link: http://lkml.kernel.org/r/ed54bfcfbe50a9070d20ec1edbe0d149e22a4568.1307292171.git.luto@mit.edu
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 7 insertions, 9 deletions

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 4f90082fd640..80174719910c 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -166,22 +166,20 @@ SECTIONS
         __vsyscall_0 = .;
 
         . = VSYSCALL_ADDR;
-        .vsyscall_0 : AT(VLOAD(.vsyscall_0)) {
+        .vsyscall : AT(VLOAD(.vsyscall)) {
                 *(.vsyscall_0)
-        } :user
 
-        . = ALIGN(L1_CACHE_BYTES);
-        .vsyscall_fn : AT(VLOAD(.vsyscall_fn)) {
+                . = ALIGN(L1_CACHE_BYTES);
                 *(.vsyscall_fn)
-        }
 
-        .vsyscall_1 ADDR(.vsyscall_0) + 1024: AT(VLOAD(.vsyscall_1)) {
+                . = 1024;
                 *(.vsyscall_1)
-        }
-        .vsyscall_2 ADDR(.vsyscall_0) + 2048: AT(VLOAD(.vsyscall_2)) {
+
+                . = 2048;
                 *(.vsyscall_2)
-        }
 
+                . = 4096;  /* Pad the whole page. */
+        } :user =0xcc
         . = ALIGN(__vsyscall_0 + PAGE_SIZE, PAGE_SIZE);
 
 #undef VSYSCALL_ADDR