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FreeBSD-EN-22:27.loader                                         Errata Notice
                                                          The FreeBSD Project

Topic:          UEFI loader failing to boot older amd64 kernels

Category:       core
Module:         loader
Announced:      2022-11-01
Affects:        FreeBSD 13.1
Corrected:      2022-10-14 03:06:13 UTC (stable/13, 13.1-STABLE)
                2022-11-01 18:03:25 UTC (releng/13.1, 13.1-RELEASE-p3)

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

The UEFI loader is the first stage of the FreeBSD boot process on UEFI systems.
Loader is responsible for loading the boot configuration, kernel and modules,
and handing control off to the kernel.

II.  Problem Description

As of FreeBSD 13.1, the UEFI loader on amd64 systems will detect if the kernel
it loaded is capable of being relocated to a different physical address than the
historical load address.  This detection relied on an ELF symbol lookup that was
not correctly filtering symbols based on their type, which caused a false
positive result for older amd64 kernels.

III. Impact

The UEFI loader would relocate the kernel to a different physical address than
expected, and the resulting kernel would fail to boot.

IV.  Workaround

This problem can be worked around by entering the loader prompt and issuing the
command: `copy_staging enable`.  Non-amd64 systems are not affected.

V.   Solution

Upgrade your system to a supported FreeBSD stable or release / security
branch (releng) dated after the correction date.  The UEFI system partition will
need to be updated with the new loader.efi.

Perform one of the following:

1) To update your system via a binary patch:

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

# freebsd-update fetch
# freebsd-update install

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-22:27/loader.patch
# fetch https://security.FreeBSD.org/patches/EN-22:27/loader.patch.asc
# gpg --verify loader.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 by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/13/                              2b31059ea701    stable/13-n252746
releng/13.1/                            1ee7e4ba70e1  releng/13.1-n250166
- -------------------------------------------------------------------------

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

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-EN-22:27.loader.asc>
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