elf: Check invalid hole in PT_LOAD segments [BZ #28838]
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Build for i686
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Commit Message
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.
---
elf/dl-map-segments.h | 3 +++
1 file changed, 3 insertions(+)
Comments
* 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,
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
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
>
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.
How about this?
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 on elf/tst-p_align3 when loading elf/tst-p_alignmod3.so, which has
the invalid p_align in PT_LOAD segments, added by
commit d8d94863ef125a392b929732b37e07dc927fbcd1
Author: H.J. Lu <hjl.tools@gmail.com>
Date: Tue Dec 21 13:42:28 2021 -0800
The loader crash is random, depending on architecture and toolchain.
Update _dl_map_segments to detect invalid holes. This fixes BZ #28838.
> > ---
> > 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,
>
> 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
>
On Tue, 1 Feb 2022 at 04:24, H.J. Lu <hjl.tools@gmail.com> wrote:
> 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.
>
I am not competent to have an opinion on the correctness of the change, but
the test passes on Launchapd's i386 and amd64 builders with it.
Cheers,
mwh
> ---
> 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,
> --
> 2.34.1
>
>
@@ -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,