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FreeBSD-EN-23:15.sanitizer                                      Errata Notice
                                                          The FreeBSD Project

Topic:          Clang sanitizer failure with ASLR enabled

Category:       contrib
Module:         compiler-rt
Announced:      2023-12-01
Affects:        FreeBSD 14.0
Corrected:      2023-11-25 09:05:09 UTC (stable/14, 14.0-STABLE)
                2023-12-01 00:38:35 UTC (releng/14.0, 14.0-RELEASE-p1)
                2023-11-25 09:05:14 UTC (stable/13, 13.2-STABLE)

For general information regarding FreeBSD Errata Notices and Security
Advisories, including descriptions of the fields above, security
branches, and the following sections, please visit
<URL:https://security.FreeBSD.org/>.

I.   Background

Compiler-RT is an implementation of various compiler runtime support routines,
provided by the LLVM project. This library also provides a number of so-called
Sanitizers, which help to catch buffer overruns, thread data races, and so on:
AddressSanitizer, ThreadSanitizer, UndefinedBehaviorSanitizer, and more.

II.  Problem Description

Some of the Sanitizers cannot work correctly when ASLR is enabled. Therefore, at
the initialization of such Sanitizers, ASLR is detected via procctl(2). If ASLR
is enabled, it is first disabled, and then the main executable containing the
Sanitizer is re-executed, after printing an appropriate message.

However, the Sanitizers work by intercepting various function calls, and by
mistake the already-intercepted procctl(2) function was used. This causes an
internal error, which usually results in a segfault.

III. Impact

Binaries linked to AddressSanitizer (using -fsanitize=address), MemorySanitizer
(using -fsanitize=memory) or ThreadSanitizer (using -fsanitize=thread) can crash
at startup with a segfault, if ASLR is enabled. Other binaries are not affected.

IV.  Workaround

If ASLR is enabled system-wide, the problem can be worked around by running the
specific binary with proccontrol(1), to temporarily disable ASLR for only that
program. For example:

   proccontrol -m aslr -s disable /path/to/example_program

V.   Solution

Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.

No reboot is necessary, but Sanitized binaries must be re-linked, because the
Sanitizer libraries are statically linked in.

Perform one of the following:

1) To update your system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms,
or the i386 platform on FreeBSD 13 and earlier, can be updated via
the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

No reboot is necessary, but Sanitized binaries must be re-linked, because the
Sanitizer libraries are statically linked in.

2) To update your system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/EN-23:15/sanitizer.patch
# fetch https://security.FreeBSD.org/patches/EN-23:15/sanitizer.patch.asc
# gpg --verify sanitizer.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

VI.  Correction details

This issue is corrected as of the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/14/                              1e4798e9677f    stable/14-n265803
releng/14.0/                            78b4c762b20b  releng/14.0-n265381
stable/13/                              7c25a53a2cb9    stable/13-n256726
- -------------------------------------------------------------------------

Run the following command to see which files were modified by a
particular commit:

# git show --stat <commit hash>

Or visit the following URL, replacing NNNNNN with the hash:

<URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>

To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:

# git rev-list --count --first-parent HEAD

VII. References

<URL:https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=275270>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-23:15.sanitizer.asc>

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