Re: [PATCH v2 3/5] signal: Add unsafe_copy_siginfo_to_user()

[Christophe Leroy]

On 9/8/21 6:17 PM, Eric W. Biederman wrote:
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> writes:
>
> > Le 02/09/2021 à 20:43, Eric W. Biederman a écrit :
> > > Christophe Leroy <christophe.leroy@xxxxxxxxxx> 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