linux-kernel - Re: [patch 01/10] x86/fpu/signal: Clarify exception handling in restore_fpregs_from

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 for Android: free password hash cracker in your pocket

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

Message-ID: <23bd92e159dba35f74fc3d3a8186dfbb3ff84f66.camel@kernel.org>
Date:   Fri, 03 Sep 2021 09:00:16 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        LKML <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [patch 01/10] x86/fpu/signal: Clarify exception handling in
 restore_fpregs_from_user()

On Thu, 2021-09-02 at 16:08 +0200, Thomas Gleixner wrote:
> On Thu, Sep 02 2021 at 16:08, Jarkko Sakkinen wrote:
> > On Wed, 2021-09-01 at 16:47 +0000, Sean Christopherson wrote:
> > > As for SGX consuming the trap number in general, it's correct.  For non-KVM usage,
> > > it's nice to have but not strictly necessary.  Any fault except #PF on ENCLS is
> > > guaranteed to be a kernel or hardware bug; SGX uses the trap number to WARN on a
> > > !#PF exception, e.g. on #GP or #UD.  Not having the trap number would mean losing
> > > those sanity checks, which have been useful in the past.
> > 
> > AFAIK, we do not consider #UD as a bug. Agree with the conclusion that SGX
> > should never #MC, I just did not get this part. #UD is something that is
> > useful for SGX run-time.
> 
> I understood that storing the trap number is useful. I was just
> questioning the #MC angle. I.e. pretending that the #MC caused by ENCLS
> is recoverable.

Absolutely not. 

I mixed up #UD caused by CPU executing inside enclave and ENCLS causing
#UD. Sorry about that.

Because of KVM we have to catch #PF's, given that a new power cycle
in the host resets the state of SGX protected memory in the guest.

> 
> Thanks,
> 
>         tglx

/Jarkko