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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 09:20:18 -0000
SRU template updated, PPA rebuilt, Merge requests updated.
Also bundled another bug fix.
Waiting for MR review now.
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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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