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authorChristian Krinitsin <mail@krinitsin.com>2025-07-07 17:23:11 +0000
committerChristian Krinitsin <mail@krinitsin.com>2025-07-07 17:23:11 +0000
commitc50b0c4da17b6e83640e4ed2380fffb5f507c846 (patch)
treeb4f203fce1380e2ea3578a784bb8ee060fe42cbd /results/classifier/zero-shot-user-mode/output/instruction/1749393
parent61361f925d4914a6608a0076e64cc2399311ed5f (diff)
downloadqemu-analysis-c50b0c4da17b6e83640e4ed2380fffb5f507c846.tar.gz
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add zero-shot results
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+instruction: 0.613
+runtime: 0.288
+syscall: 0.099
+
+
+
+sbrk() not working under qemu-user with a PIE-compiled binary?
+
+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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