linux-kernel - [PATCH AUTOSEL 4.19 33/39] kbuild: mkcompile_h: consider timestamp if KBUILD_BUILD

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20210714194625.55303-33-sashal@kernel.org>
Date:   Wed, 14 Jul 2021 15:46:18 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Matthias Maennich <maennich@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sasha Levin <sashal@...nel.org>, linux-kbuild@...r.kernel.org
Subject: [PATCH AUTOSEL 4.19 33/39] kbuild: mkcompile_h: consider timestamp if KBUILD_BUILD_TIMESTAMP is set

From: Matthias Maennich <maennich@...gle.com>

[ Upstream commit a979522a1a88556e42a22ce61bccc58e304cb361 ]

To avoid unnecessary recompilations, mkcompile_h does not regenerate
compile.h if just the timestamp changed.
Though, if KBUILD_BUILD_TIMESTAMP is set, an explicit timestamp for the
build was requested, in which case we should not ignore it.

If a user follows the documentation for reproducible builds [1] and
defines KBUILD_BUILD_TIMESTAMP as the git commit timestamp, a clean
build will have the correct timestamp. A subsequent cherry-pick (or
amend) changes the commit timestamp and if an incremental build is done
with a different KBUILD_BUILD_TIMESTAMP now, that new value is not taken
into consideration. But it should for reproducibility.

Hence, whenever KBUILD_BUILD_TIMESTAMP is explicitly set, do not ignore
UTS_VERSION when making a decision about whether the regenerated version
of compile.h should be moved into place.

[1] https://www.kernel.org/doc/html/latest/kbuild/reproducible-builds.html

Signed-off-by: Matthias Maennich <maennich@...gle.com>
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 scripts/mkcompile_h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/scripts/mkcompile_h b/scripts/mkcompile_h
index 87f1fc9801d7..662fe19da990 100755
--- a/scripts/mkcompile_h
+++ b/scripts/mkcompile_h
@@ -78,15 +78,23 @@ UTS_TRUNCATE="cut -b -$UTS_LEN"
 # Only replace the real compile.h if the new one is different,
 # in order to preserve the timestamp and avoid unnecessary
 # recompilations.
-# We don't consider the file changed if only the date/time changed.
+# We don't consider the file changed if only the date/time changed,
+# unless KBUILD_BUILD_TIMESTAMP was explicitly set (e.g. for
+# reproducible builds with that value referring to a commit timestamp).
 # A kernel config change will increase the generation number, thus
 # causing compile.h to be updated (including date/time) due to the
 # changed comment in the
 # first line.
 
+if [ -z "$KBUILD_BUILD_TIMESTAMP" ]; then
+   IGNORE_PATTERN="UTS_VERSION"
+else
+   IGNORE_PATTERN="NOT_A_PATTERN_TO_BE_MATCHED"
+fi
+
 if [ -r $TARGET ] && \
-      grep -v 'UTS_VERSION' $TARGET > .tmpver.1 && \
-      grep -v 'UTS_VERSION' .tmpcompile > .tmpver.2 && \
+      grep -v $IGNORE_PATTERN $TARGET > .tmpver.1 && \
+      grep -v $IGNORE_PATTERN .tmpcompile > .tmpver.2 && \
       cmp -s .tmpver.1 .tmpver.2; then
    rm -f .tmpcompile
 else
-- 
2.30.2