linux-kernel - Re: [PATCH v3 1/3] x86/ldt: Make modify

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: <20150724063710.GA19245@nazgul.tnic>
Date:	Fri, 24 Jul 2015 08:37:10 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"security@...nel.org" <security@...nel.org>,
	X86 ML <x86@...nel.org>, Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	xen-devel <xen-devel@...ts.xen.org>, stable@...r.kernel.org
Subject: Re: [PATCH v3 1/3] x86/ldt: Make modify_ldt synchronous

On Wed, Jul 22, 2015 at 12:23:46PM -0700, Andy Lutomirski wrote:
> modify_ldt has questionable locking and does not synchronize
> threads.  Improve it: redesign the locking and synchronize all
> threads' LDTs using an IPI on all modifications.
> 
> This will dramatically slow down modify_ldt in multithreaded
> programs, but there shouldn't be any multithreaded programs that
> care about modify_ldt's performance in the first place.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Andy Lutomirski <luto@...nel.org>

...

> +struct ldt_struct {
> +	/*
> +	 * Xen requires page-aligned LDTs with special permissions.  This is
> +	 * needed to prevent us from installing evil descriptors such as
> +	 * call gates.  On native, we could merge the ldt_struct and LDT
> +	 * allocations, but it's not worth trying to optimize.

I don't think baremetal should care about xen and frankly, this is
getting ridiculous, slowly - baremetal has to wait with a potentially
critical security fix just because it breaks xen. Dammit, this level of
intrusiveness into x86 should've never been allowed.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--
--
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/