linux-hardening - Re: [PATCH v10 01/15] modpost: fix removing numeric suffixes

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Message-ID: <CAK7LNAQus0vcWLCgSdMZNcYKam4fKYj9c8Zrb3HggZ7dTBUrxQ@mail.gmail.com>
Date:   Tue, 24 May 2022 22:40:51 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
Cc:     linux-hardening@...r.kernel.org, X86 ML <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
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Subject: Re: [PATCH v10 01/15] modpost: fix removing numeric suffixes

On Tue, May 24, 2022 at 8:34 PM Alexander Lobakin
<alexandr.lobakin@...el.com> wrote:
>
> From: Masahiro Yamada <masahiroy@...nel.org>
> Date: Tue, 24 May 2022 03:04:00 +0900
>
> > On Thu, Feb 10, 2022 at 3:59 AM Alexander Lobakin
> > <alexandr.lobakin@...el.com> wrote:
> > >
> > > `-z unique-symbol` linker flag which is planned to use with FG-KASLR
> > > to simplify livepatching (hopefully globally later on) triggers the
> > > following:
> > >
> > > ERROR: modpost: "param_set_uint.0" [vmlinux] is a static EXPORT_SYMBOL
> > >
> > > The reason is that for now the condition from remove_dot():
> > >
> > > if (m && (s[n + m] == '.' || s[n + m] == 0))
> > >
> > > which was designed to test if it's a dot or a '\0' after the suffix
> > > is never satisfied.
> > > This is due to that `s[n + m]` always points to the last digit of a
> > > numeric suffix, not on the symbol next to it (from a custom debug
> > > print added to modpost):
> > >
> > > param_set_uint.0, s[n + m] is '0', s[n + m + 1] is '\0'
> > >
> > > So it's off-by-one and was like that since 2014.
> > > Fix this for the sake of upcoming features, but don't bother
> > > stable-backporting, as it's well hidden -- apart from that LD flag,
> > > can be triggered only by GCC LTO which never landed upstream.
> > >
> > > Fixes: fcd38ed0ff26 ("scripts: modpost: fix compilation warning")
> > > Signed-off-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> > > ---
> > >  scripts/mod/modpost.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> > > index 6bfa33217914..4648b7afe5cc 100644
> > > --- a/scripts/mod/modpost.c
> > > +++ b/scripts/mod/modpost.c
> > > @@ -1986,7 +1986,7 @@ static char *remove_dot(char *s)
> > >
> > >         if (n && s[n]) {
> > >                 size_t m = strspn(s + n + 1, "0123456789");
> > > -               if (m && (s[n + m] == '.' || s[n + m] == 0))
> > > +               if (m && (s[n + m + 1] == '.' || s[n + m + 1] == 0))
> > >                         s[n] = 0;
> > >
> > >                 /* strip trailing .lto */
> > > --
> > > 2.34.1
> > >
> >
> > This trivial patch has not been picked up yet.
> >
> > I can apply this to my tree, if you want.
>
> It's a good idea, I'd like to!
> I don't use `-z unique-symbol` for FG-KALSR anymore*, but this fix
> is not directly related to it and can be taken independently.
> Should I change the commit message or it's ok to take it as it is?


I am fine with either way.

If you want to resubmit this with a fresh commit log,
please send it to:
  linux-kbuild@...r.kernel.org

Then, I will take care of it in this MW.

Thanks.




> >
> > Please let me know your thoughts.
> >
> >
> > --
> > Best Regards
> > Masahiro Yamada
>
> * I'm planning to submit a new rev of FG-KASLR series soon, but
> since I'm too busy with XDP for now, it will happen no sooner than
> in a couple months =\
>
> Thanks!
> Al



-- 
Best Regards
Masahiro Yamada