[PATCH v3 07/10] x86-64: Fill unused parts of the vsyscall page with 0xcc

[Andy Lutomirski <luto@MIT.EDU>]

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>
---
 arch/x86/kernel/vmlinux.lds.S |   16 +++++++---------
 1 files changed, 7 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 1583238..8d6a0b7 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
-- 
1.7.5.1