linux-kernel - Re: [PATCH 1/2] x86: Check return values from early

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Date:   Wed, 12 Oct 2022 17:26:09 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Ross Philipson <ross.philipson@...cle.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        dpsmith@...rtussolutions.com, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, luto@...capital.net, dave.hansen@...ux.intel.com,
        kanth.ghatraju@...cle.com, trenchboot-devel@...glegroups.com,
        Jan Kiszka <jan.kiszka@...mens.com>,
        jailhouse-dev@...glegroups.com, xen-devel@...ts.xenproject.org,
        Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: [PATCH 1/2] x86: Check return values from early_memremap calls

On 12.10.22 17:13, Ross Philipson wrote:
> On 10/8/22 11:12, Borislav Petkov wrote:
>> Adding Xen and Jailhouse people and MLs to Cc.
>>
>> Folks, thread starts here:
>>
>> https://lore.kernel.org/r/1650035401-22855-1-git-send-email-ross.philipson@oracle.com
>>
>> On Fri, Apr 15, 2022 at 11:10:00AM -0400, Ross Philipson wrote:
>>> There are a number of places where early_memremap is called
>>> but the return pointer is not checked for NULL. The call
>>> can result in a NULL being returned so the checks must
>>> be added.
>>>
>>> Signed-off-by: Ross Philipson <ross.philipson@...cle.com>
>>> ---
>>>   arch/x86/kernel/devicetree.c | 10 ++++++++++
>>>   arch/x86/kernel/e820.c       |  5 +++++
>>>   arch/x86/kernel/jailhouse.c  |  6 ++++++
>>>   arch/x86/kernel/mpparse.c    | 23 +++++++++++++++++++++++
>>>   arch/x86/kernel/setup.c      |  5 +++++
>>>   arch/x86/xen/enlighten_hvm.c |  2 ++
>>>   arch/x86/xen/mmu_pv.c        |  8 ++++++++
>>>   arch/x86/xen/setup.c         |  2 ++
>>>   8 files changed, 61 insertions(+)
>>
>> Ok, a couple of notes:
>>
>> 1. the pr_*("<prefix>:" ... )
>>
>> thing is done using pr_fmt() - grep the tree for examples.
> 
> I am already using the pr_* macros in the patches. Are you asking me to do 
> something or is this just informational?
> 
>>
>> 2. I think you should not panic() the machine but issue a the
>> warning/error and let the machine die a painful death anyway. But Xen
>> folks will know better what would be the optimal thing to do.
> 
> When I was working on the patches I asked Andrew Cooper at Citrix what action I 
> should take if any of the calls in the Xen code failed. I believe he told me it 
> was basically fatal and that panic() would be fine there.

panic() is the way to go. Everything else would make the error harder
to analyze.

BTW, CC-ing the maintainers of the modified code is good practice.


Juergen

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