From: "H.J. Lu" <hjl.tools@gmail.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: GNU C Library <libc-alpha@sourceware.org>,
"Carlos O'Donell" <carlos@redhat.com>,
Michael Hudson-Doyle <michael.hudson@canonical.com>
Subject: Re: [PATCH] elf: Check invalid hole in PT_LOAD segments [BZ #28838]
Date: Mon, 31 Jan 2022 07:59:48 -0800 [thread overview]
Message-ID: <CAMe9rOo7_sWhkYEvoYZqYQEU6j+OvNC25NpDnjWr-Ur7O-TKqg@mail.gmail.com> (raw)
In-Reply-To: <877daf9anu.fsf@oldenburg.str.redhat.com>
On Mon, Jan 31, 2022 at 7:40 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > commit 163f625cf9becbb82dfec63a29e566324129c0cd
> > Author: H.J. Lu <hjl.tools@gmail.com>
> > Date: Tue Dec 21 12:35:47 2021 -0800
> >
> > elf: Remove excessive p_align check on PT_LOAD segments [BZ #28688]
> >
> > removed the p_align check against the page size. It caused the loader
> > crash in shared objects with the invalid p_align. Update _dl_map_segments
> > to detect invalid holes. This fixes BZ #28838.
>
> Commit message should reference commit ID and mention the failing
> test/module name.
>
> > ---
> > elf/dl-map-segments.h | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
> > index 172692b120..fd24cf5d01 100644
> > --- a/elf/dl-map-segments.h
> > +++ b/elf/dl-map-segments.h
> > @@ -113,6 +113,9 @@ _dl_map_segments (struct link_map *l, int fd,
> > unallocated. Then jump into the normal segment-mapping loop to
> > handle the portion of the segment past the end of the file
> > mapping. */
> > + if (__glibc_unlikely (loadcmds[nloadcmds - 1].mapstart <
> > + c->mapend))
> > + return N_("ELF load command address/offset not page-aligned");
> > if (__glibc_unlikely
> > (__mprotect ((caddr_t) (l->l_addr + c->mapend),
> > loadcmds[nloadcmds - 1].mapstart - c->mapend,
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If loadcmds[nloadcmds - 1].mapstart < c->mapend, the length argument
passed to __mprotect is a huge number and invalid.
>
> This seems to be fairly risky because I don't think that so far, we
> enforce increasing LOAD segment addresses (although required by te EHF
> specification).
>
> Given
>
> LDFLAGS-tst-p_alignmod3.so += -Wl,-z,max-page-size=0x100,-z,common-page-size=0x100
>
> and RELRO construction for that
>
> .../elf/tst-p_alignmod3.so: cannot change memory protections
>
> seems to be a valid failure string for this test. However, worst case,
> there could be a different kind of failure, if the RELRO mprotect start
> is page-aligned by chance, and the kernel rounds up the end address to a
> page boundary. The RELRO protection then covers more than what the link
> editor expected, and this can cause crashes later on. But this isn't
> something we can detect easily, I think.
>
> Thanks,
> Florian
>
--
H.J.
next prev parent reply other threads:[~2022-01-31 16:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-31 15:24 H.J. Lu
2022-01-31 15:39 ` Florian Weimer
2022-01-31 15:59 ` H.J. Lu [this message]
2022-01-31 16:07 ` H.J. Lu
2022-01-31 22:19 ` Michael Hudson-Doyle
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