linux-kernel - [PATCH 1/2] kbuild: Fix CFI failures with GCOV

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Message-ID: <20230623001140.1111494-5-samitolvanen@google.com>
Date:   Fri, 23 Jun 2023 00:11:42 +0000
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Kees Cook <keescook@...omium.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>, Tom Rix <trix@...hat.com>,
        linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Joe Fradley <joefradley@...gle.com>
Subject: [PATCH 1/2] kbuild: Fix CFI failures with GCOV

With GCOV_PROFILE_ALL, Clang injects __llvm_gcov_* functions to
each object file, and the functions are indirectly called during
boot. However, when code is injected to object files that are not
part of vmlinux.o, it's also not processed by objtool, which breaks
CFI hash randomization as the hashes in these files won't be
included in the .cfi_sites section and thus won't be randomized.

Similarly to commit 42633ed852de ("kbuild: Fix CFI hash
randomization with KASAN"), disable GCOV for .vmlinux.export.o and
init/version-timestamp.o to avoid emitting unnecessary functions to
object files that don't otherwise have executable code.

Fixes: 0c3e806ec0f9 ("x86/cfi: Add boot time hash randomization")
Reported-by: Joe Fradley <joefradley@...gle.com>
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 init/Makefile            | 1 +
 scripts/Makefile.vmlinux | 1 +
 2 files changed, 2 insertions(+)

diff --git a/init/Makefile b/init/Makefile
index 26de459006c4..ec557ada3c12 100644
--- a/init/Makefile
+++ b/init/Makefile
@@ -60,3 +60,4 @@ include/generated/utsversion.h: FORCE
 $(obj)/version-timestamp.o: include/generated/utsversion.h
 CFLAGS_version-timestamp.o := -include include/generated/utsversion.h
 KASAN_SANITIZE_version-timestamp.o := n
+GCOV_PROFILE_version-timestamp.o := n
diff --git a/scripts/Makefile.vmlinux b/scripts/Makefile.vmlinux
index 10176dec97ea..3cd6ca15f390 100644
--- a/scripts/Makefile.vmlinux
+++ b/scripts/Makefile.vmlinux
@@ -19,6 +19,7 @@ quiet_cmd_cc_o_c = CC      $@
 
 ifdef CONFIG_MODULES
 KASAN_SANITIZE_.vmlinux.export.o := n
+GCOV_PROFILE_.vmlinux.export.o := n
 targets += .vmlinux.export.o
 vmlinux: .vmlinux.export.o
 endif
-- 
2.41.0.162.gfafddb0af9-goog