From: Oliver Upton <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>
Cc: kvmarm@lists.linux.dev, James Morse <james.morse@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Zenghui Yu <yuzenghui@huawei.com>, Will Deacon <will@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Fuad Tabba <tabba@google.com>,
linux-arm-kernel@lists.infradead.org, surajjs@amazon.com,
Cornelia Huck <cohuck@redhat.com>,
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>,
Jing Zhang <jingzhangos@google.com>
Subject: Re: [PATCH v12 07/11] KVM: arm64: Use arm64_ftr_bits to sanitise ID register writes
Date: Thu, 15 Jun 2023 12:45:34 +0000 [thread overview]
Message-ID: <ZIsH7rbS72Cdxmfx@linux.dev> (raw)
In-Reply-To: <878rckrjcl.wl-maz@kernel.org>
Hey Marc,
On Thu, Jun 15, 2023 at 01:38:34PM +0100, Marc Zyngier wrote:
> > @@ -1528,11 +1613,31 @@ static int get_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> > static int set_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> > u64 val)
> > {
> > - /* This is what we mean by invariant: you can't change it. */
> > - if (val != read_id_reg(vcpu, rd))
> > - return -EINVAL;
> > + u32 id = reg_to_encoding(rd);
> > + int ret;
> >
> > - return 0;
> > + mutex_lock(&vcpu->kvm->arch.config_lock);
> > +
> > + /*
> > + * Once the VM has started the ID registers are immutable. Reject any
> > + * write that does not match the final register value.
> > + */
> > + if (kvm_vm_has_ran_once(vcpu->kvm)) {
> > + if (val != read_id_reg(vcpu, rd))
> > + ret = -EBUSY;
> > + else
> > + ret = 0;
> > +
> > + mutex_unlock(&vcpu->kvm->arch.config_lock);
> > + return ret;
> > + }
> > +
> > + ret = arm64_check_features(vcpu, rd, val);
> > + if (!ret)
> > + IDREG(vcpu->kvm, id) = val;
> > +
> > + mutex_unlock(&vcpu->kvm->arch.config_lock);
> > + return ret;
>
> ... we now end-up with a *new* error code that userspace was never
> able to see so far.
>
> This may not be a big deal, but I'd rather err on the side of caution
> by keeping the current, slightly less precise error code.
I completely agree, thanks for catching this. There's already enough
deliberate (theorectical) breakage brought about by this series, want to
avoid any unintended fallout :)
I plan on taking this, and I'll apply a fix on top to dumb down the
return.
--
Thanks,
Oliver
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next prev parent reply other threads:[~2023-06-15 12:46 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-09 19:00 [PATCH v12 00/11] Support writable CPU ID registers from userspace Oliver Upton
2023-06-09 19:00 ` [PATCH v12 01/11] KVM: arm64: Separate out feature sanitisation and initialisation Oliver Upton
2023-06-09 19:00 ` [PATCH v12 02/11] KVM: arm64: Relax invariance of KVM_ARM_VCPU_POWER_OFF Oliver Upton
2023-06-09 19:00 ` [PATCH v12 03/11] KVM: arm64: Make vCPU feature flags consistent VM-wide Oliver Upton
2023-06-09 19:00 ` [PATCH v12 04/11] KVM: arm64: Rewrite IMPDEF PMU version as NI Oliver Upton
2023-06-09 19:00 ` [PATCH v12 05/11] KVM: arm64: Reuse fields of sys_reg_desc for idreg Oliver Upton
2023-06-09 19:00 ` [PATCH v12 06/11] KVM: arm64: Save ID registers' sanitized value per guest Oliver Upton
2023-06-09 19:00 ` [PATCH v12 07/11] KVM: arm64: Use arm64_ftr_bits to sanitise ID register writes Oliver Upton
2023-06-15 12:38 ` Marc Zyngier
2023-06-15 12:45 ` Oliver Upton [this message]
2023-06-09 19:00 ` [PATCH v12 08/11] KVM: arm64: Use generic sanitisation for ID_(AA64)DFR0_EL1 Oliver Upton
2023-06-09 19:00 ` [PATCH v12 09/11] KVM: arm64: Use generic sanitisation for ID_AA64PFR0_EL1 Oliver Upton
2023-06-09 19:00 ` [PATCH v12 10/11] KVM: arm64: Handle ID register reads using the VM-wide values Oliver Upton
2023-06-09 19:00 ` [PATCH v12 11/11] KVM: arm64: Rip out the vestiges of the 'old' ID register scheme Oliver Upton
2023-06-09 19:08 ` [PATCH v12 00/11] Support writable CPU ID registers from userspace Oliver Upton
2023-06-15 13:20 ` Oliver Upton
2023-06-15 13:30 ` Marc Zyngier
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