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

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Message-ID: <ZzurZX_wm08tyD79@desktop>
Date: Mon, 18 Nov 2024 13:02:29 -0800
From: "Ragavendra B.N." <ragavendra.bn@...il.com>
To: Tom Lendacky <thomas.lendacky@....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 Mon, Nov 18, 2024 at 02:37:58PM -0600, Tom Lendacky wrote:
> On 11/18/24 14:22, Ragavendra B.N. wrote:
> > On Mon, Nov 18, 2024 at 01:50:55PM -0600, Tom Lendacky wrote:
> >> 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.
> > 
> > I am assuming something like below.
> > 
> > /* Check if exception information from hypervisor is sane. */
> > if ((info & SVM_EVTINJ_VALID) &&
> > 		((v == X86_TRAP_GP) || (v == X86_TRAP_UD)) &&
> > 		((info & SVM_EVTINJ_TYPE_MASK) == SVM_EVTINJ_TYPE_EXEPT)) {
> > 
> > 	memset(ctxt->fi, 0, sizeof(es_fault_info));
> > 
> > 	ctxt->fi.vector = v;
> > 
> > PS - My C skills is not that great as well, as I am from Java/ C# background.
> 
> Yes, that is the general idea.
> 
> Please be sure that whatever you submit builds properly before
> submitting. For example, the above will fail to build (as would have
> your first patch).
> 
> Be sure to read Documentation/process/coding-style.rst and
> Documentation/process/submitting-patches.rst.
> 
> Thanks,
> Tom
> 
> > 
> > 
> > Thanks,
> > Ragavendra N.

Sure Tom, I will certainly check if I can build correctly and read the suggested documentation as well before sending my patch.


Thanks & regards,
Ragavendra