linux-kernel - Re: [PATCH v4 63/75] x86/sev-es: Handle #DB Events

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: <20200715100808.GL16200@suse.de>
Date:   Wed, 15 Jul 2020 12:08:08 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Joerg Roedel <joro@...tes.org>, x86@...nel.org, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jiri Slaby <jslaby@...e.cz>,
        Dan Williams <dan.j.williams@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Juergen Gross <jgross@...e.com>,
        Kees Cook <keescook@...omium.org>,
        David Rientjes <rientjes@...gle.com>,
        Cfir Cohen <cfir@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mike Stunes <mstunes@...are.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Martin Radev <martin.b.radev@...il.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v4 63/75] x86/sev-es: Handle #DB Events

On Wed, Jul 15, 2020 at 11:51:36AM +0200, Peter Zijlstra wrote:
> On Wed, Jul 15, 2020 at 11:13:37AM +0200, Joerg Roedel wrote:
> > Then my understanding of intrumentation_begin/end() is wrong, I thought
> > that the kernel will forbid setting breakpoints before
> > instrumentation_begin(), which is necessary here because a break-point
> > in the #VC handler might cause recursive #VC-exceptions when #DB is
> > intercepted.
> > Maybe you can elaborate on why this makes no sense?
> 
> Kernel avoids breakpoints in any noinstr text, irrespective of
> instrumentation_begin().
> 
> instrumentation_begin() merely allows one to call !noinstr functions.

Right, but the handler calls into various other functions. I actually
started to annotate them all with noinstr, but that was a can of worms
when calling into generic kernel functions. And the only problem with
intrumentation in the #VC handler is the #VC-for-#DB exit-code, so I
decided to only handle this one with instrumentation forbidden and allow
it for the rest of the handler.

Regards,

	Joerg