module: sign with sha512 instead of sha1 by default

Switch away from using sha1 for module signing by default and use the
more modern sha512 instead, which is what among others Arch, Fedora,
RHEL, and Ubuntu are currently using for their kernels.

Sha1 has not been considered secure against well-funded opponents since
2005[1]; since 2011 the NIST and other organizations furthermore
recommended its replacement[2]. This is why OpenSSL on RHEL9, Fedora
Linux 41+[3], and likely some other current and future distributions
reject the creation of sha1 signatures, which leads to a build error of
allmodconfig configurations:

  80A20474797F0000:error:03000098:digital envelope routines:do_sigver_init:invalid digest:crypto/evp/m_sigver.c:342:
  make[4]: *** [.../certs/Makefile:53: certs/signing_key.pem] Error 1
  make[4]: *** Deleting file 'certs/signing_key.pem'
  make[4]: *** Waiting for unfinished jobs....
  make[3]: *** [.../scripts/Makefile.build:478: certs] Error 2
  make[2]: *** [.../Makefile:1936: .] Error 2
  make[1]: *** [.../Makefile:224: __sub-make] Error 2
  make[1]: Leaving directory '...'
  make: *** [Makefile:224: __sub-make] Error 2

This change makes allmodconfig work again and sets a default that is
more appropriate for current and future users, too.

Link: https://www.schneier.com/blog/archives/2005/02/cryptanalysis_o.html
Link: https://csrc.nist.gov/projects/hash-functions
Link: https://fedoraproject.org/wiki/Changes/OpenSSLDistrustsha1SigVer
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Tested-by: kdevops <kdevops@lists.linux.dev> [0]
Link: https://github.com/linux-kdevops/linux-modules-kpd/actions/runs/11420092929/job/31775404330
Link: https://lore.kernel.org/r/52ee32c0c92afc4d3263cea1f8a1cdc809728aff.1729088288.git.linux@leemhuis.info
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>

diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig
index 7b329057997ad2ec310133ca84617d9bfcdb7e9f..74fe976e3b010f7c0516cfc16fb15018d5561d8b 100644 (file)
--- a/kernel/module/Kconfig
+++ b/kernel/module/Kconfig
@@ -231,6 +231,7 @@ comment "Do not forget to sign required modules with scripts/sign-file"
 choice
        prompt "Hash algorithm to sign modules"
        depends on MODULE_SIG || IMA_APPRAISE_MODSIG
+       default MODULE_SIG_SHA512
        help
          This determines which sort of hashing algorithm will be used during
          signature generation.  This algorithm _must_ be built into the kernel