linux-kernel - Re: [RFC PATCH] KVM: arm64: don't single-step for non-emulated faults

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: <CAFEAcA8mKCTeswpiznVWR3kSfVfjbot1aTSfemFVNjzXYdSJwA@mail.gmail.com>
Date:   Wed, 7 Nov 2018 17:53:20 +0000
From:   Peter Maydell <peter.maydell@...aro.org>
To:     Alex Bennée <alex.bennee@...aro.org>
Cc:     kvm-devel <kvm@...r.kernel.org>,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
        kvmarm@...ts.cs.columbia.edu,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] KVM: arm64: don't single-step for non-emulated faults

On 7 November 2018 at 17:39, Peter Maydell <peter.maydell@...aro.org> wrote:
> On 7 November 2018 at 17:10, Alex Bennée <alex.bennee@...aro.org> wrote:
>> Not all faults handled by handle_exit are instruction emulations. For
>> example a ESR_ELx_EC_IABT will result in the page tables being updated
>> but the instruction that triggered the fault hasn't actually executed
>> yet. We use the simple heuristic of checking for a changed PC before
>> seeing if kvm_arm_handle_step_debug wants to claim we stepped an
>> instruction.
>>
>> Signed-off-by: Alex Bennée <alex.bennee@...aro.org>
>
> What's the rationale for this change? Presumably it's fixing
> something, but the commit message doesn't really say what...
>
> This feels to me like it's working around the fact that
> we've separated two things ("advance pc (or set it if we're
> going to make the guest take an exception)" and "notice that
> we have completed a single step") that should be handled
> at one point in the code.

...so for instance if your guest PC is at the entrypoint for
an exception, and you singlestep and take the same exception
again, this should count as a single step completed, even
though the PC has not changed. Granted, that's a little
contrived, but it can happen in cases where the guest gets
completely confused and is sitting in a tight loop taking
exceptions because there's no ram at the vector table
address, or whatever.

thanks
-- PMM