linux-kernel - Re: [PATCH v2 4/6] KVM: arm64: Limit length in kvm_vm_ioctl_mte_copy_tags() to INT

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Date:   Wed, 08 Feb 2023 16:03:22 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     Thomas Huth <thuth@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Cc:     kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Gavin Shan <gshan@...hat.com>,
        Steven Price <steven.price@....com>
Subject: Re: [PATCH v2 4/6] KVM: arm64: Limit length in
 kvm_vm_ioctl_mte_copy_tags() to INT_MAX

On Wed, Feb 08 2023, Thomas Huth <thuth@...hat.com> wrote:

> In case of success, this function returns the amount of handled bytes.
> However, this does not work for large values: The function is called
> from kvm_arch_vm_ioctl() (which still returns a long), which in turn
> is called from kvm_vm_ioctl() in virt/kvm/kvm_main.c. And that function
> stores the return value in an "int r" variable. So the upper 32-bits
> of the "long" return value are lost there.
>
> KVM ioctl functions should only return "int" values, so let's limit
> the amount of bytes that can be requested here to INT_MAX to avoid
> the problem with the truncated return value. We can then also change
> the return type of the function to "int" to make it clearer that it
> is not possible to return a "long" here.
>
> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
> Signed-off-by: Thomas Huth <thuth@...hat.com>
> ---
>  Documentation/virt/kvm/api.rst    | 3 ++-
>  arch/arm64/include/asm/kvm_host.h | 4 ++--
>  arch/arm64/kvm/guest.c            | 8 ++++++--
>  3 files changed, 10 insertions(+), 5 deletions(-)

Reviewed-by: Cornelia Huck <cohuck@...hat.com>