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 19:05:45 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Brijesh Singh <brijesh.singh@....com>,
        Al Viro <viro@...IV.linux.org.uk>
Cc:     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 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!

Paolo