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From:   Tim Merrifield <tim.merrifield@broadcom.com>
Date:   Tue, 5 Dec 2023 16:43:16 -0600
Message-ID: <CAJfbqWyeubVofe4BHQC+a3wacwk0kMPECa8mxZ7gkzhBJ3d5LA@mail.gmail.com>
Subject: Re: [PATCH v2 6/6] x86/vmware: Add TDX hypercall support
To:     Alexey Makhalov <alexey.makhalov@broadcom.com>
Cc:     Dave Hansen <dave.hansen@intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Alexey Makhalov <amakhalov@vmware.com>,
        linux-kernel@vger.kernel.org, virtualization@lists.linux.dev,
        hpa@zytor.com, dave.hansen@linux.intel.co, mingo@redhat.com,
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        richardcochran@gmail.com, linux-input@vger.kernel.org,
        dmitry.torokhov@gmail.com, zackr@vmware.com,
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        namit@vmware.com, timothym@vmware.com, akaher@vmware.com,
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        horms@kernel.org
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Hi Dave and Alexey,

Regarding VMware-specific checks, it may be beneficial to add some
additional checks
such as ensuring that the hypervisor vendor is VMware,
r12=3D=3DVMWARE_HYPERVISOR_MAGIC,
r10=3D=3DVMWARE_TDX_VENDOR_LEAF, r11=3D=3DVMWARE_TDX_HCALL_FUNC and r13 (co=
mmand) is
restricted to those few commands we expect to be invoked from the
kernel or drivers by VMware-specific
code.

If we add these checks, would folks be OK with exporting this function?


On Tue, Dec 5, 2023 at 3:41=E2=80=AFPM Alexey Makhalov
<alexey.makhalov@broadcom.com> wrote:
>
>
>
> On 12/5/23 1:24 PM, Dave Hansen wrote:
> > On 12/4/23 02:31, Borislav Petkov wrote:
> >> On Fri, Dec 01, 2023 at 03:24:52PM -0800, Alexey Makhalov wrote:
> >>> +#ifdef CONFIG_INTEL_TDX_GUEST
> >>> +/* __tdx_hypercall() is not exported. So, export the wrapper */
> >>> +void vmware_tdx_hypercall_args(struct tdx_module_args *args)
> >>> +{
> >>> +   __tdx_hypercall(args);
> >>> +}
> >>> +EXPORT_SYMBOL_GPL(vmware_tdx_hypercall_args);
> >> Uuuh, lovely. I'd like to see what the TDX folks think about this
> >> export first.
> >
> > I don't really like it much.  This does a generic thing (make a TDX
> > hypercall) with a specific name ("vmware_").  If you want to make an
> > argument that a certain chunk of the __tdx_hypercall() space is just fo=
r
> > VMWare and you also add a VMWare-specific check and then export *that*,
> > it might be acceptable.
> >
> > But I don't want random modules able to make random, unrestricted TDX
> > hypercalls.  That's asking for trouble.
>
> Considering exporting of __tdx_hypercall for random modules is not an
> option, what VMware specific checks you are suggesting?
>
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