linux-kernel - [tip:x86/vdso] x86, vdso: Zero-pad the VVAR page

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Date:	Wed, 5 Mar 2014 14:32:37 -0800
From:	tip-bot for Andy Lutomirski <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, luto@...capital.net, hpa@...or.com,
	mingo@...nel.org, stefani@...bold.net, tglx@...utronix.de,
	hpa@...ux.intel.com
Subject: [tip:x86/vdso] x86, vdso: Zero-pad the VVAR page

Commit-ID:  bab2c42e8a52d5a76009ad805c97060377f98fdf
Gitweb:     http://git.kernel.org/tip/bab2c42e8a52d5a76009ad805c97060377f98fdf
Author:     Andy Lutomirski <luto@...capital.net>
AuthorDate: Mon, 3 Mar 2014 22:12:23 +0100
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Wed, 5 Mar 2014 14:02:39 -0800

x86, vdso: Zero-pad the VVAR page

By coincidence, the VVAR page is at the end of an ELF segment.  As a
result, if it ends up being a partial page, the kernel loader will
leave garbage behind at the end of the vvar page.  Zero-pad it to a
full page to fix this issue.

This has probably been broken since the VVAR page was introduced.
On QEMU, if you dump the run-time contents of the VVAR page, you can
find entertaining strings from seabios left behind.

It's remotely possible that this is a security bug -- conceivably
there's some BIOS out there that leaves something sensitive in the
few K of memory that is exposed to userspace.

Signed-off-by: Stefani Seibold <stefani@...bold.net>
Link: http://lkml.kernel.org/r/1393881143-3569-13-git-send-email-stefani@seibold.net
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
---
 arch/x86/kernel/vmlinux.lds.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 1d4897b..49edf2d 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -164,6 +164,11 @@ SECTIONS
 #undef __VVAR_KERNEL_LDS
 #undef EMIT_VVAR
 
+		/*
+		 * Pad the rest of the page with zeros.  Otherwise the loader
+		 * can leave garbage here.
+		 */
+		. = __vvar_beginning_hack + PAGE_SIZE;
 	} :data
 
        . = ALIGN(__vvar_page + PAGE_SIZE, PAGE_SIZE);
--
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