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Re: [PATCH] linux-user/host/s390: Treat EX and EXRL as writes

From: Thomas Huth
Subject: Re: [PATCH] linux-user/host/s390: Treat EX and EXRL as writes
Date: Wed, 4 May 2022 15:46:41 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0

On 04/05/2022 13.48, Ilya Leoshkevich wrote:
clang-built s390x branch-relative-long test fails on clang-built s390x
QEMU due to the following sequence of events:

- The test zeroes out a code page, clang generates exrl+xc for this.

- do_helper_xc() is called. Clang generates exrl+xc there as well.

- Since there already exists a TB for the code in question, its page is
   read-only and SIGSEGV is raised.

- host_signal_handler() calls host_signal_write() and the latter does
   not recognize exrl as a write. Therefore page_unprotect() is not
   called and the signal is forwarded to the test.

Fix by treating EXRL (and EX, just in case) as writes. There may be
false positives, but they will lead only to an extra page_unprotect()

Reported-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
  linux-user/include/host/s390/host-signal.h | 7 +++++++
  1 file changed, 7 insertions(+)

Great, this fixes the crash for me, indeed! Thank you!

Tested-by: Thomas Huth <thuth@redhat.com>

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