linux-kernel - Re: [PATCH] KVM: x86: Account for 32-bit kernels when handling address in TSC attrs

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Message-ID: <CAOQ_Qsj9yiChnBZmotdYFYgsd=C0J5XXR8mthdiC+iXX22F7jw@mail.gmail.com>
Date:   Mon, 11 Oct 2021 09:35:11 -0500
From:   Oliver Upton <oupton@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Account for 32-bit kernels when handling
 address in TSC attrs

On Thu, Oct 7, 2021 at 6:16 PM Sean Christopherson <seanjc@...gle.com> wrote:
>
> When handling TSC attributes, cast the userspace provided virtual address
> to an unsigned long before casting it to a pointer to fix warnings on
> 32-bit kernels due to casting a 64-bit integer to a 32-bit pointer.
>
> Add a check that the truncated address matches the original address, e.g.
> to prevent userspace specifying garbage in bits 63:32.
>
>   arch/x86/kvm/x86.c: In function ‘kvm_arch_tsc_get_attr’:
>   arch/x86/kvm/x86.c:4947:22: error: cast to pointer from integer of different size
>    4947 |  u64 __user *uaddr = (u64 __user *)attr->addr;
>         |                      ^
>   arch/x86/kvm/x86.c: In function ‘kvm_arch_tsc_set_attr’:
>   arch/x86/kvm/x86.c:4967:22: error: cast to pointer from integer of different size
>    4967 |  u64 __user *uaddr = (u64 __user *)attr->addr;
>         |                      ^
>
> Cc: Oliver Upton <oupton@...gle.com>
> Fixes: 469fde25e680 ("KVM: x86: Expose TSC offset controls to userspace")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/kvm/x86.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>

Reviewed-by: Oliver Upton <oupton@...gle.com>