linux-kernel - [PATCH v2 07/10] x86-64: Fill unused parts of the vsyscall page with 0xcc

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Date:	Sun, 29 May 2011 23:48:44 -0400
From:	Andy Lutomirski <luto@....EDU>
To:	Ingo Molnar <mingo@...e.hu>, x86@...nel.org
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	Jesper Juhl <jj@...osbits.net>, Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Andy Lutomirski <luto@....edu>
Subject: [PATCH v2 07/10] 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@....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

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