module: Remove SHA-1 support for module signing

SHA-1 is considered deprecated and insecure due to vulnerabilities that can
lead to hash collisions. Most distributions have already been using SHA-2
for module signing because of this. The default was also changed last year
from SHA-1 to SHA-512 in commit f3b93547b9 ("module: sign with sha512
instead of sha1 by default"). This was not reported to cause any issues.
Therefore, it now seems to be a good time to remove SHA-1 support for
module signing.

Commit 16ab7cb582 ("crypto: pkcs7 - remove sha1 support") previously
removed support for reading PKCS#7/CMS signed with SHA-1, along with the
ability to use SHA-1 for module signing. This change broke iwd and was
subsequently completely reverted in commit 203a6763ab ("Revert "crypto:
pkcs7 - remove sha1 support""). However, dropping only the support for
using SHA-1 for module signing is unrelated and can still be done
separately.

Note that this change only removes support for new modules to be SHA-1
signed, but already signed modules can still be loaded.

Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Reviewed-by: Aaron Tomlin <atomlin@atomlin.com>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

kernel/module/Kconfig

@@ -299,10 +299,6 @@ choice
 	  possible to load a signed module containing the algorithm to check
 	  the signature on that module.
 
-config MODULE_SIG_SHA1
-	bool "SHA-1"
-	select CRYPTO_SHA1
-
 config MODULE_SIG_SHA256
 	bool "SHA-256"
 	select CRYPTO_SHA256
@@ -332,7 +328,6 @@ endchoice
 config MODULE_SIG_HASH
 	string
 	depends on MODULE_SIG || IMA_APPRAISE_MODSIG
-	default "sha1" if MODULE_SIG_SHA1
 	default "sha256" if MODULE_SIG_SHA256
 	default "sha384" if MODULE_SIG_SHA384
 	default "sha512" if MODULE_SIG_SHA512