linux-kernel - [PATCH v21 12/12] x86: Zero-pad the VVAR page

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <1393752020-6740-13-git-send-email-stefani@seibold.net>
Date:	Sun,  2 Mar 2014 10:20:20 +0100
From:	Stefani Seibold <stefani@...bold.net>
To:	gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, ak@...ux.intel.com, aarcange@...hat.com,
	john.stultz@...aro.org, luto@...capital.net, xemul@...allels.com,
	gorcunov@...nvz.org, andriy.shevchenko@...ux.intel.com
Cc:	Martin.Runge@...de-schwarz.com, Andreas.Brief@...de-schwarz.com,
	Stefani Seibold <stefani@...bold.net>
Subject: [PATCH v21 12/12] x86: 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: Andy Lutomirski <luto@...capital.net>
Signed-off-by: Stefani Seibold <stefani@...bold.net>
---
 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);
-- 
1.9.0

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/