linux-hardening - [PATCH] kbuild: merge module sections under CONFIG_LD_DEAD_CODE_DATA

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Message-ID: <20210402123959.5143-1-alobakin@pm.me>
Date:   Fri, 02 Apr 2021 12:40:08 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jessica Yu <jeyu@...nel.org>, Miroslav Benes <mbenes@...e.cz>,
        Emil Velikov <emil.l.velikov@...il.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexander Lobakin <alobakin@...me>,
        linux-hardening@...r.kernel.org, linux-kbuild@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] kbuild: merge module sections under CONFIG_LD_DEAD_CODE_DATA_ELIMINATION too

When building with CONFIG_LD_DEAD_CODE_DATA_ELIMINATION,
-fdata-sections and -ffunction-sections are being enabled by the
top-level Makefile, and module section merging is also needed.
Expand the ifdef (and the comment block) to cover that case too.

Fixes: 6a3193cdd5e5 ("kbuild: lto: Merge module sections if and only if CONFIG_LTO_CLANG is enabled")
Signed-off-by: Alexander Lobakin <alobakin@...me>
---
 scripts/module.lds.S | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 2c52535f9b56..d6bbdfc55e08 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -20,11 +20,14 @@ SECTIONS {

 	__patchable_function_entries : { *(__patchable_function_entries) }

-#ifdef CONFIG_LTO_CLANG
+#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG)
 	/*
 	 * With CONFIG_LTO_CLANG, LLD always enables -fdata-sections and
-	 * -ffunction-sections, which increases the size of the final module.
-	 * Merge the split sections in the final binary.
+	 * -ffunction-sections. With CONFIG_LD_DEAD_CODE_DATA_ELIMINATION,
+	 * -fdata-sections and -ffunction-sections are being enabled by
+	 * the top-level Makefile.
+	 * This increases the size of the final module. Merge the split
+	 * sections in the final binary.
 	 */
 	.bss : {
 		*(.bss .bss.[0-9a-zA-Z_]*)
--
2.31.1