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SubjectRe: [PATCH] KVM: SVM: Fix sparse: incorrect type in argument 1 (different base types)
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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.

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