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

[Oliver Upton]

On Thu, Oct 7, 2021 at 6:16 PM Sean Christopherson <seanjc@xxxxxxxxxx> 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@xxxxxxxxxx>
> Fixes: 469fde25e680 ("KVM: x86: Expose TSC offset controls to userspace")
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/kvm/x86.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>

Reviewed-by: Oliver Upton <oupton@xxxxxxxxxx>