linux-kernel - Re: [PATCH] retpoline/module: Taint kernel for missing retpoline in module

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Message-ID: <20180113153644.GA25956@kroah.com>
Date:   Sat, 13 Jan 2018 16:36:44 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     tglx@...utronix.de, dwmw@...zon.co.uk,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        arjan.van.de.ven@...el.com, peterz@...radead.org,
        Andi Kleen <ak@...ux.intel.com>, jeyu@...nel.org
Subject: Re: [PATCH] retpoline/module: Taint kernel for missing retpoline in
 module

On Sat, Jan 13, 2018 at 06:53:00AM -0800, Andi Kleen wrote:
> > > When the a module hasn't been compiled with a retpoline
> > > aware compiler, print a warning and set a taint flag.
> > 
> > Isn't that caught by the "build with a different compiler/version" check
> > that we have?  Or used to have?  If not, can't we just make it into that
> 
> - the compiler version number may not change if a distribution backports
> the gcc changes for the new flag
> - the module might be using a custom make file that does not correctly
> set the flag, even if the compiler supports it
> 
> > type of check to catch this type of problem no matter what type of
> > feature/option it is trying to catch?
> 
> I suspect that would be far more complicated.

Really?  As Arjan points out, just mix it into the modversion symbol
generation, that should cause it to be caught properly and trivially.

> Also what's the point of putting this information into every symbol?

It makes it easy to check :)

> Once per module is good enough.
> 
> We already have similar checks for staging etc.

Sure, but this is more of a "Hey, your version of GCC is doing something
different than what you built the kernel with, watch out!" which is much
more generic and good to know.  A whole taint for one CPU bug type seems
overkill to me.

thanks,

greg k-h