From: Dave Hansen <dave.hansen@intel.com>
To: "Huang, Kai" <kai.huang@intel.com>,
"isaku.yamahata@gmail.com" <isaku.yamahata@gmail.com>
Cc: "kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"david@redhat.com" <david@redhat.com>,
"bagasdotme@gmail.com" <bagasdotme@gmail.com>,
"ak@linux.intel.com" <ak@linux.intel.com>,
"Wysocki, Rafael J" <rafael.j.wysocki@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"Chatre, Reinette" <reinette.chatre@intel.com>, "Christopherson,,
Sean" <seanjc@google.com>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"Yamahata, Isaku" <isaku.yamahata@intel.com>,
"kirill.shutemov@linux.intel.com"
<kirill.shutemov@linux.intel.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"Luck, Tony" <tony.luck@intel.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"Shahar, Sagi" <sagis@google.com>,
"imammedo@redhat.com" <imammedo@redhat.com>,
"Gao, Chao" <chao.gao@intel.com>,
"Brown, Len" <len.brown@intel.com>,
"sathyanarayanan.kuppuswamy@linux.intel.com"
<sathyanarayanan.kuppuswamy@linux.intel.com>,
"Huang, Ying" <ying.huang@intel.com>,
"Williams, Dan J" <dan.j.williams@intel.com>
Subject: Re: [PATCH v10 05/16] x86/virt/tdx: Add skeleton to enable TDX on demand
Date: Tue, 14 Mar 2023 08:48:38 -0700 [thread overview]
Message-ID: <5c4a28c8-f17d-7395-cc63-3cbd9b31befb@intel.com> (raw)
In-Reply-To: <a62497059fc3f31706a532b822d6c966bd981468.camel@intel.com>
On 3/13/23 18:50, Huang, Kai wrote:
> On Mon, 2023-03-13 at 16:49 -0700, Isaku Yamahata wrote:
>> On Sun, Mar 12, 2023 at 11:08:44PM +0000,
>> "Huang, Kai" <kai.huang@intel.com> wrote:
>>
>>> On Wed, 2023-03-08 at 14:27 -0800, Isaku Yamahata wrote:
>>>>> +
>>>>> +static int try_init_module_global(void)
>>>>> +{
>>>>> + int ret;
>>>>> +
>>>>> + /*
>>>>> + * The TDX module global initialization only needs to be done
>>>>> + * once on any cpu.
>>>>> + */
>>>>> + spin_lock(&tdx_global_init_lock);
>>>>> +
>>>>> + if (tdx_global_init_status & TDX_GLOBAL_INIT_DONE) {
>>>>> + ret = tdx_global_init_status & TDX_GLOBAL_INIT_FAILED ?
>>>>> + -EINVAL : 0;
>>>>> + goto out;
>>>>> + }
>>>>> +
>>>>> + /* All '0's are just unused parameters. */
>>>>> + ret = seamcall(TDH_SYS_INIT, 0, 0, 0, 0, NULL, NULL);
>>>>> +
>>>>> + tdx_global_init_status = TDX_GLOBAL_INIT_DONE;
>>>>> + if (ret)
>>>>> + tdx_global_init_status |= TDX_GLOBAL_INIT_FAILED;
>>>>
>>>> If entropy is lacking (rdrand failure), TDH_SYS_INIT can return TDX_SYS_BUSY.
>>>> In such case, we should allow the caller to retry or make this function retry
>>>> instead of marking error stickily.
>>>
>>> The spec says:
>>>
>>> TDX_SYS_BUSY The operation was invoked when another TDX module
>>> operation was in progress. The operation may be retried.
>>>
>>> So I don't see how entropy is lacking is related to this error. Perhaps you
>>> were mixing up with KEY.CONFIG?
>>
>> TDH.SYS.INIT() initializes global canary value. TDX module is compiled with
>> strong stack protector enabled by clang and canary value needs to be
>> initialized. By default, the canary value is stored at
>> %fsbase:<STACK_CANARY_OFFSET 0x28>
>>
>> Although this is a job for libc or language runtime, TDX modules has to do it
>> itself because it's stand alone.
>>
>> From tdh_sys_init.c
>> _STATIC_INLINE_ api_error_type tdx_init_stack_canary(void)
>> {
>> ia32_rflags_t rflags = {.raw = 0};
>> uint64_t canary;
>> if (!ia32_rdrand(&rflags, &canary))
>> {
>> return TDX_SYS_BUSY;
>> }
>> ...
>> last_page_ptr->stack_canary.canary = canary;
>>
>>
>
> Then it is a hidden behaviour of the TDX module that is not reflected in the
> spec.
This is true. Could you please go ask the TDX module folks to fix this up?
> I am not sure whether we should handle because:
>
> 1) This is an extremely rare case. Kernel would be basically under attack if
> such error happened. In the current series we don't handle such case in
> KEY.CONFIG either but just leave a comment (see patch 13).
Rare, yes. Under attack? I'm not sure where you get that from. Look
at the SDM:
> Under heavy load, with multiple cores executing RDRAND in parallel, it is possible, though unlikely, for the demand
> of random numbers by software processes/threads to exceed the rate at which the random number generator
> hardware can supply them. This will lead to the RDRAND instruction returning no data transitorily. The RDRAND
> instruction indicates the occurrence of this rare situation by clearing the CF flag.
That doesn't talk about attacks.
> 2) Not sure whether this will be changed in the future.
>
> So I think we should keep as is.
TDX_SYS_BUSY really is missing some nuance. You *REALLY* want to retry
RDRAND failures. But, if you have VMM locking and don't expect two
users calling into the TDX module then TDX_SYS_BUSY from a busy *module*
is a bad (and probably fatal) signal.
I suspect we should just throw a few retries in the seamcall()
infrastructure to retry in the case of TDX_SYS_BUSY. It'll take care of
RDRAND failures. If a retry loop fails to resolve it, then we should
probably dump a warning and return an error.
Just do this once, in common code.
next prev parent reply other threads:[~2023-03-14 15:51 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 14:13 [PATCH v10 00/16] TDX host kernel support Kai Huang
2023-03-06 14:13 ` [PATCH v10 01/16] x86/tdx: Define TDX supported page sizes as macros Kai Huang
2023-03-16 12:37 ` David Hildenbrand
2023-03-16 22:41 ` Huang, Kai
2023-03-06 14:13 ` [PATCH v10 02/16] x86/virt/tdx: Detect TDX during kernel boot Kai Huang
2023-03-16 12:48 ` David Hildenbrand
2023-03-16 22:37 ` Huang, Kai
2023-03-23 17:02 ` David Hildenbrand
2023-03-23 22:15 ` Huang, Kai
2023-03-06 14:13 ` [PATCH v10 03/16] x86/virt/tdx: Make INTEL_TDX_HOST depend on X86_X2APIC Kai Huang
2023-03-16 12:57 ` David Hildenbrand
2023-03-06 14:13 ` [PATCH v10 04/16] x86/virt/tdx: Add SEAMCALL infrastructure Kai Huang
2023-03-06 14:13 ` [PATCH v10 05/16] x86/virt/tdx: Add skeleton to enable TDX on demand Kai Huang
2023-03-08 22:27 ` Isaku Yamahata
2023-03-12 23:08 ` Huang, Kai
2023-03-13 23:49 ` Isaku Yamahata
2023-03-14 1:50 ` Huang, Kai
2023-03-14 4:02 ` Isaku Yamahata
2023-03-14 5:45 ` Dave Hansen
2023-03-14 17:16 ` Isaku Yamahata
2023-03-14 17:38 ` Dave Hansen
2023-03-14 15:48 ` Dave Hansen [this message]
2023-03-15 11:10 ` Huang, Kai
2023-03-16 22:07 ` Huang, Kai
2023-03-23 13:49 ` Dave Hansen
2023-03-23 22:09 ` Huang, Kai
2023-03-23 22:12 ` Dave Hansen
2023-03-23 22:42 ` Huang, Kai
2023-03-16 0:31 ` Isaku Yamahata
2023-03-16 2:45 ` Isaku Yamahata
2023-03-16 2:52 ` Huang, Kai
2023-03-06 14:13 ` [PATCH v10 06/16] x86/virt/tdx: Get information about TDX module and TDX-capable memory Kai Huang
2023-03-06 14:13 ` [PATCH v10 07/16] x86/virt/tdx: Use all system memory when initializing TDX module as TDX memory Kai Huang
2023-03-09 1:38 ` Isaku Yamahata
2023-03-06 14:13 ` [PATCH v10 08/16] x86/virt/tdx: Add placeholder to construct TDMRs to cover all TDX memory regions Kai Huang
2023-03-06 14:13 ` [PATCH v10 09/16] x86/virt/tdx: Fill out " Kai Huang
2023-03-06 14:13 ` [PATCH v10 10/16] x86/virt/tdx: Allocate and set up PAMTs for TDMRs Kai Huang
2023-03-21 7:44 ` Dong, Eddie
2023-03-21 8:05 ` Huang, Kai
2023-03-06 14:13 ` [PATCH v10 11/16] x86/virt/tdx: Designate reserved areas for all TDMRs Kai Huang
2023-03-06 14:13 ` [PATCH v10 12/16] x86/virt/tdx: Configure TDX module with the TDMRs and global KeyID Kai Huang
2023-03-06 14:13 ` [PATCH v10 13/16] x86/virt/tdx: Configure global KeyID on all packages Kai Huang
2023-03-06 14:13 ` [PATCH v10 14/16] x86/virt/tdx: Initialize all TDMRs Kai Huang
2023-03-06 14:14 ` [PATCH v10 15/16] x86/virt/tdx: Flush cache in kexec() when TDX is enabled Kai Huang
2023-03-06 14:14 ` [PATCH v10 16/16] Documentation/x86: Add documentation for TDX host support Kai Huang
2023-03-08 1:11 ` [PATCH v10 00/16] TDX host kernel support Isaku Yamahata
2023-03-16 12:35 ` David Hildenbrand
2023-03-16 22:06 ` Huang, Kai
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