linux-kernel - Re: [PATCH 7/7] KVM: TDX: Add TSX_CTRL msr into uret

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <c9b14955-6e2f-4490-a18c-0537ffdfff30@intel.com>
Date: Wed, 4 Dec 2024 13:55:33 +0200
From: Adrian Hunter <adrian.hunter@...el.com>
To: Chao Gao <chao.gao@...el.com>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "seanjc@...gle.com" <seanjc@...gle.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "Li, Xiaoyao" <xiaoyao.li@...el.com>, "Huang, Kai" <kai.huang@...el.com>,
 "Zhao, Yan Y" <yan.y.zhao@...el.com>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "Yang, Weijiang" <weijiang.yang@...el.com>,
 "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
 "dmatlack@...gle.com" <dmatlack@...gle.com>,
 "pbonzini@...hat.com" <pbonzini@...hat.com>,
 "Yamahata, Isaku" <isaku.yamahata@...el.com>,
 "tony.lindgren@...ux.intel.com" <tony.lindgren@...ux.intel.com>,
 "nik.borisov@...e.com" <nik.borisov@...e.com>,
 "Chatre, Reinette" <reinette.chatre@...el.com>,
 "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH 7/7] KVM: TDX: Add TSX_CTRL msr into uret_msrs list

On 4/12/24 13:13, Chao Gao wrote:
> On Wed, Dec 04, 2024 at 08:57:23AM +0200, Adrian Hunter wrote:
>> On 4/12/24 08:37, Chao Gao wrote:
>>> On Wed, Dec 04, 2024 at 08:18:32AM +0200, Adrian Hunter wrote:
>>>> On 4/12/24 03:25, Chao Gao wrote:
>>>>>> +#define TDX_FEATURE_TSX (__feature_bit(X86_FEATURE_HLE) | __feature_bit(X86_FEATURE_RTM))
>>>>>> +
>>>>>> +static bool has_tsx(const struct kvm_cpuid_entry2 *entry)
>>>>>> +{
>>>>>> +	return entry->function == 7 && entry->index == 0 &&
>>>>>> +	       (entry->ebx & TDX_FEATURE_TSX);
>>>>>> +}
>>>>>> +
>>>>>> +static void clear_tsx(struct kvm_cpuid_entry2 *entry)
>>>>>> +{
>>>>>> +	entry->ebx &= ~TDX_FEATURE_TSX;
>>>>>> +}
>>>>>> +
>>>>>> +static bool has_waitpkg(const struct kvm_cpuid_entry2 *entry)
>>>>>> +{
>>>>>> +	return entry->function == 7 && entry->index == 0 &&
>>>>>> +	       (entry->ecx & __feature_bit(X86_FEATURE_WAITPKG));
>>>>>> +}
>>>>>> +
>>>>>> +static void clear_waitpkg(struct kvm_cpuid_entry2 *entry)
>>>>>> +{
>>>>>> +	entry->ecx &= ~__feature_bit(X86_FEATURE_WAITPKG);
>>>>>> +}
>>>>>> +
>>>>>> +static void tdx_clear_unsupported_cpuid(struct kvm_cpuid_entry2 *entry)
>>>>>> +{
>>>>>> +	if (has_tsx(entry))
>>>>>> +		clear_tsx(entry);
>>>>>> +
>>>>>> +	if (has_waitpkg(entry))
>>>>>> +		clear_waitpkg(entry);
>>>>>> +}
>>>>>> +
>>>>>> +static bool tdx_unsupported_cpuid(const struct kvm_cpuid_entry2 *entry)
>>>>>> +{
>>>>>> +	return has_tsx(entry) || has_waitpkg(entry);
>>>>>> +}
>>>>>
>>>>> No need to check TSX/WAITPKG explicitly because setup_tdparams_cpuids() already
>>>>> ensures that unconfigurable bits are not set by userspace.
>>>>
>>>> Aren't they configurable?
>>>
>>> They are cleared from the configurable bitmap by tdx_clear_unsupported_cpuid(),
>>> so they are not configurable from a userspace perspective. Did I miss anything?
>>> KVM should check user inputs against its adjusted configurable bitmap, right?
>>
>> Maybe I misunderstand but we rely on the TDX module to reject
>> invalid configuration.  We don't check exactly what is configurable
>> for the TDX Module.
> 
> Ok, this is what I missed. I thought KVM validated user input and masked
> out all unsupported features. sorry for this.
> 
>>
>> TSX and WAITPKG are not invalid for the TDX Module, but KVM
>> must either support them by restoring their MSRs, or disallow
>> them.  This patch disallows them for now.
> 
> Yes. I agree. what if a new feature (supported by a future TDX module) also
> needs KVM to restore some MSRs? current KVM will allow it to be exposed (since
> only TSX/WAITPKG are checked); then some MSRs may get corrupted. I may think
> this is not a good design. Current KVM should work with future TDX modules.

With respect to CPUID, I gather this kind of thing has been
discussed, such as here:

	https://lore.kernel.org/all/ZhVsHVqaff7AKagu@google.com/

and Rick and Xiaoyao are working on something.

In general, I would expect a new TDX Module would advertise support for
new features, but KVM would have to opt in to use them.