linux-kernel - Re: [PATCH] KVM: arm64: Use different pointer authentication keys for pKVM

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Date:   Wed, 14 Jun 2023 13:28:18 +0100
From:   Mostafa Saleh <smostafa@...gle.com>
To:     Oliver Upton <oliver.upton@...ux.dev>
Cc:     kvmarm@...ts.linux.dev, maz@...nel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        suzuki.poulose@....com, kaleshsingh@...gle.com, tabba@...gle.com,
        yuzenghui@...wei.com, catalin.marinas@....com, james.morse@....com,
        will@...nel.org
Subject: Re: [PATCH] KVM: arm64: Use different pointer authentication keys for pKVM

On Tue, Jun 13, 2023 at 5:27 PM Mostafa Saleh <smostafa@...gle.com> wrote:
>
> Hi Oliver,
>
> On Tue, Jun 13, 2023 at 12:16:02PM +0000, Oliver Upton wrote:
> > On Tue, 16 May 2023 14:15:31 +0000, Mostafa Saleh wrote:
> > > When the kernel is compiled with CONFIG_ARM64_PTR_AUTH_KERNEL, it
> > > uses Armv8.3-Pauth for return address protection for the kernel code
> > > including nvhe code in EL2.
> > >
> > > Same keys are used in both kernel(EL1) and nvhe code(EL2), this is
> > > fine for nvhe but not when running in protected mode(pKVM) as the host
> > > can't be trusted.
> > >
> > > [...]
> >
> > Applied to kvmarm/next, thanks!
> >
> > [1/1] KVM: arm64: Use different pointer authentication keys for pKVM
> >       https://git.kernel.org/kvmarm/kvmarm/c/fb737685beee
> >
> > --
>
> Thanks! I did more testing and I found a bug in this patch.
>
> It seems there is another entry point for the kenrel where pauth was
> not handled properly "kvm_host_psci_cpu_entry", I will investigate this
> further and send V2.
>
> Sorry for the inconvenience!
>
> Thanks,
> Mostafa

I investigated the problem further and actually the bug is missing
isb() after updating
Pauth system registers at EL2, I sent a v2 with this fix.

Although when entering from kvm_host_psci_cpu_entry, the hyp keys are not used,
but this call directly exists to the host, so I believe this should be fine.