linux-kernel - Re: [PATCH v5] kallsyms: new /proc/kallmodsyms with builtin modules

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Message-ID: <202109301051.DDD8B5F27@keescook>
Date:   Thu, 30 Sep 2021 10:53:35 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Nick Alcock <nick.alcock@...cle.com>
Cc:     jeyu@...nel.org, masahiroy@...nel.org,
        linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
        arnd@...db.de, eugene.loh@...cle.com, kris.van.hees@...cle.com
Subject: Re: [PATCH v5] kallsyms: new /proc/kallmodsyms with builtin modules

On Thu, Sep 30, 2021 at 06:19:55PM +0100, Nick Alcock wrote:
> On 30 Sep 2021, Kees Cook said:
> > On Wed, Sep 29, 2021 at 10:51:47PM +0100, Nick Alcock wrote:
> >> It would be useful if there were a mapping between kernel symbol and module
> >> name that only changed when the kernel source code is changed.  This mapping
> >> should not change simply because a module becomes built into the kernel.
> >> 
> >> It might also be useful if there were reliable symbol size information to
> >> determine whether an address is within a symbol or outside it, especially
> >> given that there could be huge gaps between symbols.
> >> [...]
> > [...]
> > It would be useful, sure, but is there something that does, in fact,
> > need this, or would like this if it were available? Since this provides
> > a userspace API, what would be consuming that API? For example, when
> > Syscall User Dispatch was added, it was clear it was for Wine[1].
> 
> We have a long-term consumer in DTrace (e.g.
> <https://github.com/oracle/dtrace-utils/blob/dev/libdtrace/dt_module.c#L1323>).
> (But since we control this consumer we are quite happy to change the
> format of kallmodsyms, integrate it with kallsyms so that kallsyms just
> provides the same information if the file format break were acceptable,
> or whatever you think most sensible. We just want this information
> somehow. :) e.g. the code there doesn't yet handle the
> symbol-in-multiple-modules case: I'll have to add that.)

Ah-ha, excellent. That works for me. :) (If there is a v5, maybe add a
note about DTrace to help show the specific need.)

Thanks!

-Kees

-- 
Kees Cook