linux-kernel - Re: [PATCH] KVM: SVM: Fix sparse: incorrect type in argument 1 (different base types)

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Date:   Fri, 23 Feb 2018 12:26:40 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Al Viro <viro@...IV.linux.org.uk>
Cc:     brijesh.singh@....com, kvm@...r.kernel.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Borislav Petkov <bp@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: SVM: Fix sparse: incorrect type in argument 1
 (different base types)



On 02/23/2018 12:05 PM, Paolo Bonzini wrote:
> On 22/02/2018 16:56, Brijesh Singh wrote:
>>
>>
>> On 02/21/2018 02:18 PM, Al Viro wrote:
>>> On Wed, Feb 21, 2018 at 01:59:55PM -0600, Brijesh Singh wrote:
>>>
>>>> Sure, checking access_ok() does not guarantee that later
>>>> copy_from_user() will not fail. But it does eliminate one possible
>>>> reason for the failure. We are trying to validate most of the user
>>>> inputs before we invoke  SEV command.
>>>
>>> That makes no sense whatsoever.  If user is deliberately fuzzing
>>> your code or trying to DoS it, that "validation" doesn't buy you
>>> anything - they can just as well feed you NULL, after all.
>>>
>>
>>
>> Currently, we let user query the blob length with params.len == 0 ||
>> param.uaddr == NULL. We could limit it to just params.len == 0.
>>
>>
>>> What is the rationale for that?  "Userland is accidentally feeding
>>> us garbage pointers" is the case where slowness is the least of your
>>> concerns...
>>>
>>
>> My intent was to do some obvious failure checks on user inputs before
>> invoking the HW. I do see your point that if userspace is feeding us
>> garbage then slowness is least of our concern. If you think that we
>> should not be using access_ok() in this particular case then I am okay
>> with it.
> 
> Can you please send a patch?  Thanks!
> 

Sure, I will send patch soon.

-Brijesh