Re: [Xen-devel] [PATCH] x86emul/fuzz: adjust canonicalization in sanitize_input()

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Mar 29, 2019, at 3:23 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
> 
>>>> On 29.03.19 at 16:14, <George.Dunlap@xxxxxxxxxx> wrote:
> 
>> 
>>> On Mar 29, 2019, at 2:51 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>> 
>>> Drop it entirely for %rbp - this register is not special purpose enough
>>> to warrant such special treatment. Add a comment to clarify the purpose
>>> of the canonicalization of %rip and %rsp.
>>> 
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> 
>> FAOD:
>> 1. I don’t oppose this, but
>> 2. I don’t support it either; however,
>> 3. I don’t think my Ack is necessary.
> 
> Well, preferably I would address your concerns despite 3. So could
> you clarify what you would suggest instead? Keep things as they
> are? Drop all canonicalization? I've basically tried to find a middle
> ground between the two extremes.

I appreciate that. :-) But the main reason I wrote this was #3: I didn’t want 
my silence interpreted as a nack.

I don’t think it will help fuzzing to remove canonicalization of ebp; it may 
help to have it in.  In fact I’d prefer to CANONICALIZE_MAYBE() more registers.

But I don’t think the question is so clear, or so important, that it’s worth 
having a long discussion about.  Absent some sort of rigorous testing, we’re 
all just guessing which is better; you & Andy are guessing one way, I’m 
guessing the other way.  This patch is about as close to middle-ground as there 
is.

Peace,
 -George
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