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From: "adhemerval.zanella at linaro dot org"
 <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/31076] Extra struct vm_area_struct with ---p
 created when PAGE_SIZE < max-page-size
Date: Mon, 27 Nov 2023 17:39:48 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31076

--- Comment #9 from Adhemerval Zanella <adhemerval.zanella at linaro dot or=
g> ---
(In reply to Florian Weimer from comment #8)
> (In reply to Adhemerval Zanella from comment #7)
> > So the mprotect is essentially a hardening feature, assuming that the
> > dynamic object padding/holes might contain gadgets.  It still does not
> > happen for loader and main program itself, since normally they would be
> > mapped by the kernel and its does do anything with holes,
>=20
> There's no expectation that these are contiguous in memory, yes. Such an
> expectation exists for shared objects loaded by glibc.

Right, but my point is if this is a hardening feature that glibc aims to
provide it does not help if the kernel still does not provide it for the lo=
ader
(if this is built with a different page size) and the main program itself.
Should we push for kernel to implement a similar handling?

And the holes seem to be always from the initial read-only segment, which m=
akes
the whole gadget avoidance argument moot. This would make sense back when R=
ELRO
was not wildly used/deployed (even with the current somewhat broken status),
but it still does not make much sense to me.

>=20
> > and IMHO it should
> > up to the static linker to fill the padding with NOP/trap instruction to
> > avoid such issues.=20
>=20
> That requires padding to the maximum page size on disk, though.

But this is what binutils does [1], and while not being optimized it seems =
that
it would be somewhat hard to fix it (at least with Fangrui Song suggestion).

[1] https://sourceware.org/bugzilla/show_bug.cgi?id=3D30612

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