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

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Message-ID: <30558bc8-c22c-1ce1-f59a-66c057fdd06f@amd.com>
Date: Mon, 18 Nov 2024 08:53:04 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Ard Biesheuvel <ardb@...nel.org>,
 "Ragavendra B.N." <ragavendra.bn@...il.com>
Cc: 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 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