linux-kernel - [PATCH v4 1/2] xen/x86: Zero out .bss for PV guests

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: <1456513357-19981-2-git-send-email-boris.ostrovsky@oracle.com>
Date:	Fri, 26 Feb 2016 14:02:36 -0500
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	konrad.wilk@...cle.com, david.vrabel@...rix.com
Cc:	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	mcgrof@...nel.org, brgerst@...il.com, andrew.cooper3@...rix.com,
	roger.pau@...rix.com, Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: [PATCH v4 1/2] xen/x86: Zero out .bss for PV guests

ELF spec is unclear about whether .bss must me cleared by the loader.
Currently the domain builder does it when loading the guest but because
it is not (or rather may not be) guaranteed we should zero it out
explicitly.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
---
 arch/x86/xen/xen-head.S | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index b65f59a..5c63d2d 100644
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -38,6 +38,15 @@
 	__INIT
 ENTRY(startup_xen)
 	cld
+
+	/* Clear .bss */
+	xor %eax,%eax
+	mov $__bss_start, %_ASM_DI
+	mov $__bss_stop, %_ASM_CX
+	sub %_ASM_DI, %_ASM_CX
+	shr $__ASM_SEL(2, 3), %_ASM_CX
+	rep __ASM_SIZE(stos)
+
 #ifdef CONFIG_X86_32
 	mov %esi,xen_start_info
 	mov $init_thread_union+THREAD_SIZE,%esp
-- 
2.1.0