linux-kernel - Re: [PATCH v2 6/6] x86/vmware: Add TDX hypercall support

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Message-ID: <bbb6225f-3610-4fcf-86e6-f7468f743d76@intel.com>
Date:   Tue, 5 Dec 2023 15:03:01 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Alexey Makhalov <alexey.makhalov@...adcom.com>,
        Borislav Petkov <bp@...en8.de>,
        Alexey Makhalov <amakhalov@...are.com>
Cc:     linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
        hpa@...or.com, dave.hansen@...ux.intel.co, bp@...en8.d,
        mingo@...hat.com, tglx@...utronix.de, x86@...nel.org,
        netdev@...r.kernel.org, richardcochran@...il.com,
        linux-input@...r.kernel.org, dmitry.torokhov@...il.com,
        zackr@...are.com, linux-graphics-maintainer@...are.com,
        pv-drivers@...are.com, namit@...are.com, timothym@...are.com,
        akaher@...are.com, jsipek@...are.com,
        dri-devel@...ts.freedesktop.org, daniel@...ll.ch,
        airlied@...il.com, tzimmermann@...e.de, mripard@...nel.org,
        maarten.lankhorst@...ux.intel.com, horms@...nel.org
Subject: Re: [PATCH v2 6/6] x86/vmware: Add TDX hypercall support

On 12/5/23 13:41, Alexey Makhalov wrote:
>> 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 for
>> 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?

Make sure it can only be called running on VMWare guests.  A check for
X86_HYPER_VMWARE seems simple enough.

Second, unless the space is *HUGE*, you want to be exporting things like
__vmware_platform() or vmware_legacy_x2apic_available(), *NOT* the
underlying hypercall functions.

We want to make sure that the interfaces are well defined and bounded.