linux-kernel - Re: [Xen-devel] [PATCH 11/13] x86/paravirt: Add paravirt alternatives infrastructure

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: <20171017210311.tvedzz5m5xsntvew@treble>
Date:   Tue, 17 Oct 2017 16:03:11 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Mike Galbraith <efault@....de>, xen-devel@...ts.xenproject.org,
        Peter Zijlstra <peterz@...radead.org>,
        Jiri Slaby <jslaby@...e.cz>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Sasha Levin <alexander.levin@...izon.com>,
        Chris Wright <chrisw@...s-sol.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        live-patching@...r.kernel.org, Alok Kataria <akataria@...are.com>,
        virtualization@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [Xen-devel] [PATCH 11/13] x86/paravirt: Add paravirt
 alternatives infrastructure

On Tue, Oct 17, 2017 at 04:59:41PM -0400, Boris Ostrovsky wrote:
> On 10/17/2017 04:50 PM, Josh Poimboeuf wrote:
> > On Tue, Oct 17, 2017 at 04:36:00PM -0400, Boris Ostrovsky wrote:
> >> On 10/17/2017 04:17 PM, Josh Poimboeuf wrote:
> >>> On Tue, Oct 17, 2017 at 11:36:57AM -0400, Boris Ostrovsky wrote:
> >>>> On 10/17/2017 10:36 AM, Josh Poimboeuf wrote:
> >>>>> Maybe we can add a new field to the alternatives entry struct which
> >>>>> specifies the offset to the CALL instruction, so apply_alternatives()
> >>>>> can find it.
> >>>> We'd also have to assume that the restore part of an alternative entry
> >>>> is the same size as the save part. Which is true now.
> >>> Why?
> >>>
> >> Don't you need to know the size of the instruction without save and
> >> restore part?
> >>
> >> + if (a->replacementlen == 6 && *insnbuf == 0xff && *(insnbuf+1) == 0x15)
> >>
> >> Otherwise you'd need another field for the actual instruction length.
> > If we know where the CALL instruction starts, and can verify that it
> > starts with "ff 15", then we know the instruction length: 6 bytes.
> > Right?
> >
> 
> Oh, OK. Then you shouldn't need a->replacementlen test(s?) in
> apply_alternatives()?

Right.  Though in the above code it was needed for a different reason,
to make sure it wasn't reading past the end of the buffer.

-- 
Josh