Fix has been merged:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=965018bea7ce79e1987
** Changed in: qemu
Status: New => Fix Committed
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https://bugs.launchpad.net/bugs/1815024
Title:
SIGILL on instruction "stck" under qemu-s390x in user mode
Status in QEMU:
Fix Committed
Bug description:
qemu-s390x in user mode crashes with SIGILL (under host architecture
x86_64, running Debian unstable) when executing target instruction
"stck" ("STORE CLOCK", see
https://www-01.ibm.com/support/docview.wss?uid=isg26480faec85f44e2385256d5200627dee&aid=1),
which is basically a kind of equivalent of Intel "rdtsc". The same
instruction works fine under qemu-s390x in system mode. The bug is
reproducible with both the qemu version distributed in Debian unstable
and with the latest upstream master (commit
47994e16b1d66411953623e7c0bf0cdcd50bd507).
This bug manifested itself as a crash of ssh-keygen program, which
uses "stck" to obtain some bits of randomness during key creation.
Bisection of the code led to the attached minimal example. Compile
with (inside an s390x system):
$ gcc -c -o test.o test.c
$ gcc -c -o rdtsc.o rdtsc.S
$ gcc -o test test.o rdtsc.o
Then run test. It will crash with SIGILL in user mode and run fine in
system mode. Also, compare with the original file at
https://github.com/openssl/openssl/blob/master/crypto/s390xcpuid.pl#L139
(there the instruction "stckf" is also used; it is probable that it
has the same problem if it is supported altogether, but it did not
test for this).
Running qemu-s390x with options -d
in_asm,out_asm,op,op_opt,exec,nochain,cpu gives the trace attached in
log.txt.
Thanks, Giovanni.
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