linux-kernel - Re: [PATCH v2 11/18] KVM: arm64: don't trap Statistical Profiling controls to EL2

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: <20200109174621.GB42593@e119886-lin.cambridge.arm.com>
Date:   Thu, 9 Jan 2020 17:46:22 +0000
From:   Andrew Murray <andrew.murray@....com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Marc Zyngier <maz@...nel.org>, kvm@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 11/18] KVM: arm64: don't trap Statistical Profiling
 controls to EL2

On Thu, Jan 09, 2020 at 05:42:51PM +0000, Mark Rutland wrote:
> Hi Andrew,
> 
> On Thu, Jan 09, 2020 at 05:25:12PM +0000, Andrew Murray wrote:
> > On Mon, Dec 23, 2019 at 12:10:42PM +0000, Andrew Murray wrote:
> > > On Mon, Dec 23, 2019 at 12:05:12PM +0000, Marc Zyngier wrote:
> > > > On 2019-12-23 11:56, Andrew Murray wrote:
> > > > > My original concern in the cover letter was in how to prevent
> > > > > the guest from attempting to use these registers in the first
> > > > > place - I think the solution I was looking for is to
> > > > > trap-and-emulate ID_AA64DFR0_EL1 such that the PMSVer bits
> > > > > indicate that SPE is not emulated.
> > > > 
> > > > That, and active trapping of the SPE system registers resulting in injection
> > > > of an UNDEF into the offending guest.
> > > 
> > > Yes that's no problem.
> > 
> > The spec says that 'direct access to [these registers] are UNDEFINED' - is it
> > not more correct to handle this with trap_raz_wi than an undefined instruction?
> 
> The term UNDEFINED specifically means treated as an undefined
> instruction. The Glossary in ARM DDI 0487E.a says for UNDEFINED:
> 
> | Indicates cases where an attempt to execute a particular encoding bit
> | pattern generates an exception, that is taken to the current Exception
> | level, or to the default Exception level for taking exceptions if the
> | UNDEFINED encoding was executed at EL0. This applies to:
> |
> | * Any encoding that is not allocated to any instruction.
> |
> | * Any encoding that is defined as never accessible at the current
> |   Exception level.
> |
> | * Some cases where an enable, disable, or trap control means an
> |   encoding is not accessible at the current Exception level.
> 
> So these should trigger an UNDEFINED exception rather than behaving as
> RAZ/WI.

OK thanks for the clarification - I'll leave it as an undefined instruction.

Thanks,

Andrew Murray

> 
> Thanks,
> Mark.