[Bug 1749393] Re: sbrk() not working under qemu-user with a PIE-compiled binary?

[Christian Ehrhardt ]

Focal

old

$ sudo apt install --reinstall qemu-user-static=1:4.2-3ubuntu6.18
Reading package lists... Done
Building dependency tree       
Reading state information... Done
0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded.
Need to get 21.3 MB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu focal-updates/universe amd64 
qemu-user-static amd64 1:4.2-3ubuntu6.18 [21.3 MB]
Fetched 21.3 MB in 1s (16.4 MB/s)           
(Reading database ... 126154 files and directories currently installed.)
Preparing to unpack .../qemu-user-static_1%3a4.2-3ubuntu6.18_amd64.deb ...
Unpacking qemu-user-static (1:4.2-3ubuntu6.18) over (1:4.2-3ubuntu6.18) ...
Setting up qemu-user-static (1:4.2-3ubuntu6.18) ...
Processing triggers for man-db (2.9.1-1) ...

ubuntu@f-1928075-qemuuserstatic:~$ sudo chroot /home/ubuntu/bullseye-arm64 
/bin/sh /debootstrap/debootstrap --second-stage
W: Failure trying to run:  /sbin/ldconfig
W: See //debootstrap/debootstrap.log for details
ubuntu@f-1928075-qemuuserstatic:~$ tail -n 2 
bullseye-arm64/debootstrap/debootstrap.log
qemu: uncaught target signal 11 (Segmentation fault) - core dumped
Segmentation fault (core dumped)

Upgrade


ubuntu@f-1928075-qemuuserstatic:~$ apt-cache policy qemu-user-static
qemu-user-static:
  Installed: 1:4.2-3ubuntu6.18
  Candidate: 1:4.2-3ubuntu6.19
  Version table:
     1:4.2-3ubuntu6.19 500
        500 http://archive.ubuntu.com/ubuntu focal-proposed/universe amd64 
Packages
 *** 1:4.2-3ubuntu6.18 500
        500 http://archive.ubuntu.com/ubuntu focal-updates/universe amd64 
Packages
        100 /var/lib/dpkg/status
     1:4.2-3ubuntu6.17 500
        500 http://security.ubuntu.com/ubuntu focal-security/universe amd64 
Packages
     1:4.2-3ubuntu6 500
        500 http://archive.ubuntu.com/ubuntu focal/universe amd64 Packages
ubuntu@f-1928075-qemuuserstatic:~$ sudo apt install qemu-user-static
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be upgraded:
  qemu-user-static
1 upgraded, 0 newly installed, 0 to remove and 65 not upgraded.
Need to get 21.3 MB of archives.
After this operation, 0 B of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu focal-proposed/universe amd64 
qemu-user-static amd64 1:4.2-3ubuntu6.19 [21.3 MB]
Fetched 21.3 MB in 2s (9092 kB/s)           
(Reading database ... 126160 files and directories currently installed.)
Preparing to unpack .../qemu-user-static_1%3a4.2-3ubuntu6.19_amd64.deb ...
Unpacking qemu-user-static (1:4.2-3ubuntu6.19) over (1:4.2-3ubuntu6.18) ...
Setting up qemu-user-static (1:4.2-3ubuntu6.19) ...
Processing triggers for man-db (2.9.1-1) ...
ubuntu@f-1928075-qemuuserstatic:~$ sudo update-binfmts  --test --display  
qemu-aarch64
qemu-aarch64 (enabled):
     package = qemu-user-static
        type = magic
      offset = 0
       magic = 
\x7f\x45\x4c\x46\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xb7\x00
        mask = 
\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff
 interpreter = /usr/bin/qemu-aarch64-static
    detector = 


Test with new versio

ubuntu@f-1928075-qemuuserstatic:~$ sudo chroot /home/ubuntu/bullseye-arm64 
/bin/sh /debootstrap/debootstrap --second-stage
I: Installing core packages...
W: Failure trying to run:  dpkg --force-depends --install 
/var/cache/apt/archives/base-passwd_3.5.51_arm64.deb
W: See //debootstrap/debootstrap.log for details
ubuntu@f-1928075-qemuuserstatic:~$ tail -n 2 
bullseye-arm64/debootstrap/debootstrap.log
dpkg: error: parsing file '/var/lib/dpkg/status' near line 5 package 'dpkg':
 duplicate value for 'Package' field


That is the good case and also a full run now completes.

$ sudo rm -rf bullseye-arm64; sudo qemu-debootstrap --arch=arm64 bullseye 
bullseye-arm64 http://ftp.debian.org/debian
I: Running command: debootstrap --arch arm64 --foreign bullseye bullseye-arm64 
http://ftp.debian.org/debian
W: Cannot check Release signature; keyring file not available 
/usr/share/keyrings/debian-archive-keyring.gpg
I: Retrieving InRelease 
I: Retrieving Packages 
...
I: Configuring tasksel...
I: Configuring libc-bin...
I: Base system installed successfully.


I can't run the docker test due to networking restrictions, but it was
the same fault and the same fix - so that should be ok. If anyone else
can test -proposed with docker please feel free to do so.

** Tags removed: verification-needed verification-needed-focal
** Tags added: verification-done verification-done-focal

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https://bugs.launchpad.net/bugs/1749393

Title:
  sbrk() not working under qemu-user with a PIE-compiled binary?

Status in QEMU:
  Fix Released
Status in qemu package in Ubuntu:
  Fix Released
Status in qemu source package in Focal:
  Fix Committed

Bug description:
  [Impact]

   * 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.

  [Test Plan]

   * 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...
  done.
  Errors were encountered while processing:
   libc-bin
  E: Sub-process /usr/bin/dpkg returned an error code (1)

  
  Second test from bug 1928075

  $ sudo qemu-debootstrap --arch=arm64 bullseye bullseye-arm64
  http://ftp.debian.org/debian

  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

  [Other Info]

   * n/a

  ---

  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():
  https://git.savannah.gnu.org/cgit/bash.git/tree/lib/malloc/malloc.c

  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:
  https://lists.gnu.org/archive/html/bug-bash/2018-02/threads.html#00080

  You can find the problematic bash binary in that .deb file:
  
http://snapshot.debian.org/archive/debian/20180206T154716Z/pool/main/b/bash/bash_4.4.18-1_i386.deb

  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:
  https://bugs.debian.org/889869
  https://bugs.debian.org/865599

  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:
  https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1518483

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