linux-kernel - Re: [PATCH] arch:x86:coco:sev: Initialize ctxt variable

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Message-ID: <182fc3f3-2b9d-5c86-b058-5d1208305cbb@amd.com>
Date: Mon, 18 Nov 2024 13:50:55 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: "Ragavendra B.N." <ragavendra.bn@...il.com>
Cc: Ard Biesheuvel <ardb@...nel.org>, Ingo Molnar <mingo@...nel.org>,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, ashish.kalra@....com,
 tzimmermann@...e.de, bhelgaas@...gle.com, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arch:x86:coco:sev: Initialize ctxt variable

On 11/18/24 13:43, Ragavendra B.N. wrote:
> On Mon, Nov 18, 2024 at 08:53:04AM -0600, Tom Lendacky wrote:
>> On 11/18/24 08:44, Tom Lendacky wrote:
>>> On 11/15/24 16:55, Ard Biesheuvel wrote:
>>>> On Fri, 15 Nov 2024 at 20:53, Ragavendra B.N. <ragavendra.bn@...il.com> wrote:
>>>>>
>>>>> On Fri, Nov 15, 2024 at 12:02:27PM +0100, Ard Biesheuvel wrote:
>>>>>> On Fri, 15 Nov 2024 at 12:01, Ingo Molnar <mingo@...nel.org> wrote:
>>>>>>>
>>>>>>>
>>>>>>> * Ragavendra <ragavendra.bn@...il.com> wrote:
>>>>>>>
>>>>>>>> Updating the ctxt value to NULL in the svsm_perform_ghcb_protocol as
>>>>>>>> it was not initialized.
>>>>>>>>
>>>>>>>> Fixes: 2e1b3cc9d7f7 (grafted) Merge tag 'arm-fixes-6.12-2' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc
>>>>>>>
>>>>>>> This 'Fixes' tag looks bogus.
>>>>>>>
>>>>>>
>>>>>> So does the patch itself - 'struct es_em_ctxt ctxt' is not a pointer.
>>>>> Thank you very much for your response. I am relatively new to kernel development.
>>>>>
>>>>> I know we can use kmalloc for memory allocation. Please advice.
>>>>>
>>>>> struct es_em_ctxt ctxt = kmalloc(sizeof(struct es_em_ctxt), GFP_KERNEL);
>>>>>
>>>>> I am thinking to update like above, but like you mentioned, ctxt is not a pointer. I can update this to be a pointer if needed.
>>>>>
>>>>
>>>> The code is fine as is. Let's end this thread here, shall we?
>>>
>>> I was assuming he got some kind of warning from some compiler options or
>>> a static checker. Is that the case Ragavendra?
>>>
>>> When I look at the code, it is possible for ctxt->fi.error_code to be
>>> left uninitialized. The simple fix is to just initialize ctxt as:
>>>
>>> 	struct es_em_ctxt ctxt = {};
>>
>> Although to cover all cases now and going forwared, the es_em_ctxt fi
>> member should just be zeroed in verify_exception_info() when
>> ES_EXCEPTION is going to be returned.
>>
>> Thanks,
>> Tom
>>
>>>
>>> Thanks,
>>> Tom
> 
> Yes Tom, that is exactly the reason I worked on it the first place. The issue was reported by the Coverity tool.
> 
> I can send the below fix if that is fine.
>>> 	struct es_em_ctxt ctxt = {};
> 
> For the es_em_ctxt fi member to be zeroed, I can go ahead and assign 0 to all the three long members like below in verify_exception_info()
> 
> 
> 	if (info & SVM_EVTINJ_VALID_ERR) {
> 		ctxt->fi.error_code = info >> 32;
> 	} else {
> 		ctxt->fi.error_code = 0;
> 		ctxt->fi.vector = 0;
> 		ctxt->fi.cr2 = 0;

But then the cr2 value isn't set/zeroed in the true path of the if
statement. I think a simple memset() at the beginning of the if path
that will return ES_EXCEPTION is simplest.

Thanks,
Tom

> 
> 	}
> 
> return ES_EXCEPTION;
> 
> Thanks,
> Ragavendra N.