linux-kernel - Re: [PATCH v2 3/5] signal: Add unsafe_copy_siginfo_to

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Message-ID: <7caf5127-36fc-7c77-00f1-7be82d6f26e0@csgroup.eu>
Date:   Fri, 10 Sep 2021 10:27:03 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 3/5] signal: Add unsafe_copy_siginfo_to_user()



On 9/8/21 6:17 PM, Eric W. Biederman wrote:
> Christophe Leroy <christophe.leroy@...roup.eu> writes:
> 
>> Le 02/09/2021 à 20:43, Eric W. Biederman a écrit :
>>> Christophe Leroy <christophe.leroy@...roup.eu> writes:
>>>
>>>> In the same spirit as commit fb05121fd6a2 ("signal: Add
>>>> unsafe_get_compat_sigset()"), implement an 'unsafe' version of
>>>> copy_siginfo_to_user() in order to use it within user access blocks.
>>>>
>>>> For that, also add an 'unsafe' version of clear_user().
>>>
>>> Looking at your use cases you need the 32bit compat version of this
>>> as well.
>>>
>>> The 32bit compat version is too complicated to become a macro, so I
>>> don't think you can make this work correctly for the 32bit compat case.
>>
>> When looking into patch 5/5 that you nacked, I think you missed the fact that we
>> keep using copy_siginfo_to_user32() as it for the 32 bit compat case.
> 
> I did.  My mistake.
> 
> However that mistake was so easy I think it mirrors the comments others
> have made that this looks like a maintenance hazard.
> 
> Is improving the performance of 32bit kernels interesting?

Yes it is, and that's what this series do.

> Is improving the performance of 32bit compat support interesting?

For me this is a corner case, so I left it aside for now.

> 
> If performance one or either of those cases is interesting it looks like
> we already have copy_siginfo_to_external32 the factor you would need
> to build unsafe_copy_siginfo_to_user32.

I'm not sure I understand your saying here. What do you expect me to do 
with copy_siginfo_to_external32() ?

copy_siginfo_to_user32() is for compat only.

Native 32 bits powerpc use copy_siginfo_to_user()

> 
> So I am not going to say impossible but please make something
> maintainable.  I unified all of the compat 32bit siginfo logic because
> it simply did not get enough love and attention when it was implemented
> per architecture.

Yes, and ? I didn't do any modification to the compat case, so what you 
did remains.


> 
> In general I think that concern applies to this case as well.  We really
> need an implementation that shares as much burden as possible with other
> architectures.

I think yes, that's the reason why I made a generic 
unsafe_copy_siginfo_to_user() and didn't make a powerpc dedicated change.

Once this is merged any other architecture can use 
unsafe_copy_siginfo_to_user().

Did I miss something ?

Christophe