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[Bug 1749393] Re: sbrk() not working under qemu-user with a PIE-compiled
[Bug 1749393] Re: sbrk() not working under qemu-user with a PIE-compiled binary?
Tue, 30 Nov 2021 19:28:22 -0000
Hello Raphaël, or anyone else affected,
Accepted qemu into focal-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/qemu/1:4.2-3ubuntu6.19
in a few hours, and then in the -proposed repository.
Please help us by testing this new package. See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed. Your feedback will aid us getting this
update out to other Ubuntu users.
If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
focal to verification-done-focal. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-focal. In either case, without details of your testing we will
not be able to proceed.
Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in
advance for helping!
N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.
** Changed in: qemu (Ubuntu Focal)
Status: In Progress => Fix Committed
** Tags added: verification-needed verification-needed-focal
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sbrk() not working under qemu-user with a PIE-compiled binary?
Status in QEMU:
Status in qemu package in Ubuntu:
Status in qemu source package in Focal:
* The current space reserved can be too small and we can end up
with no space at all for BRK. It can happen to any case, but is
much more likely with the now common PIE binaries.
* Backport the upstream fix which reserves a bit more space while loading
and giving it back after interpreter and stack is loaded.
* On x86 run:
sudo apt install -y qemu-user-static docker.io
sudo docker run --rm arm64v8/debian:bullseye bash -c 'apt update && apt
install -y wget'
Running hooks in /etc/ca-certificates/update.d...
Errors were encountered while processing:
E: Sub-process /usr/bin/dpkg returned an error code (1)
Second test from bug 1928075
$ sudo qemu-debootstrap --arch=arm64 bullseye bullseye-arm64
In the bad case this is failing like
W: Failure trying to run: /sbin/ldconfig
W: See //debootstrap/debootstrap.log for detail
And in that log file you'll see the segfault
$ tail -n 2 bullseye-arm64/debootstrap/debootstrap.log
qemu: uncaught target signal 11 (Segmentation fault) - core dumped
Segmentation fault (core dumped)
[Where problems could occur]
* Regressions would be around use-cases of linux-user that is
emulation not of a system but of binaries.
Commonly uses for cross-tests and cross-builds so that is the
space to watch for regressions
In Debian unstable, we recently switched bash to be a PIE-compiled
binary (for hardening). Unfortunately this resulted in bash being
broken when run under qemu-user (for all target architectures, host
being amd64 for me).
$ sudo chroot /srv/chroots/sid-i386/ qemu-i386-static /bin/bash
bash: xmalloc: .././shell.c:1709: cannot allocate 10 bytes (0 bytes allocated)
bash has its own malloc implementation based on sbrk():
When we disable this internal implementation and rely on glibc's
malloc, then everything is fine. But it might be that glibc has a
fallback when sbrk() is not working properly and it might hide the
underlying problem in qemu-user.
This issue has also been reported to the bash upstream author and he
suggested that the issue might be in qemu-user so I'm opening a ticket here.
Here's the discussion with the bash upstream author:
You can find the problematic bash binary in that .deb file:
The version of qemu I have been using is 2.11 (Debian package qemu-
user-static version 1:2.11+dfsg-1) but I have had reports that the
problem is reproducible with older versions (back to 2.8 at least).
Here are the related Debian bug reports:
It's worth noting that bash used to have this problem (when compiled as a PIE
binary) even when run directly but then something got fixed in the kernel and
now the problem only appears when run under qemu-user:
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