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Date: Sat, 26 Sep 2020 11:09:52 +0200
From: Szabolcs Nagy <nsz@port70.net>
To: Fangrui Song <i@maskray.me>
Cc: musl@lists.openwall.com, Rich Felker <dalias@libc.org>
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	Rich Felker <dalias@libc.org>
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Subject: Re: [musl] SIGSEGV with TEXTREL

* Fangrui Song <i@maskray.me> [2020-09-25 21:14:18 -0700]:
> On Fri, Sep 25, 2020 at 7:53 PM Dominic Chen <d.c.ddcc@gmail.com> wrote:
> >
> > On 9/25/2020 6:46 PM, Rich Felker wrote:
> > >
> > > The right way to make this more friendly, I think, would be tracking
> > > the writable mapping range for each DSO (technically this is
> > > incomplete since it could be multiple ranges, but in that case we'd
> > > just take the convex hull of them and accept false negatives because
> > > anything else is almost surely too big a performance hit), and
> > > erroring out before processing a relocation at an address that's not
> > > writable for its DSO. This would also go part of the way towards
> > > making it possible for ldd to process untrusted files.
> >
> > I agree that that seems to be a better solution, and it was also
> > discussed in the previous mailing list thread. But my point is just that
> > given how this issue has been reoccurring, I think it'd be useful to do
> > something now (e.g. emit a non-fail warning if TEXTRELs are present),
> > rather than deferring any changes.
> >
> > Thanks,
> >
> > Dominic
> 
> binutils 2.35 can be configured with --enable-textrel-check=yes, and
> Linux/x86 defaults to 'yes'. ld emits a warning upon a text
> relocation:
> 
> warning: creating DT_TEXTREL in a PIE
> 
> (LLD always disallows text relocations by default (-z text). You need
> -z notext to enable DF_TEXTREL and text relocations.)

nice

and gcc passes -z text for static pie code so that case should
not end up with text rels.