[PATCH v2 2/3] x86/build: Warn on orphan section placement

From: Kees Cook <keescook@chromium.org>
To: Borislav Petkov <bp@suse.de>
Cc: Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	clang-built-linux@googlegroups.com, linux-arch@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2 2/3] x86/build: Warn on orphan section placement
Date: Mon, 22 Jun 2020 13:53:40 -0700	[thread overview]
Message-ID: <20200622205341.2987797-3-keescook@chromium.org> (raw)
In-Reply-To: <20200622205341.2987797-1-keescook@chromium.org>

We don't want to depend on the linker's orphan section placement
heuristics as these can vary between linkers, and may change between
versions. All sections need to be explicitly named in the linker
script.

Discards the unused rela, plt, and got sections that are not needed
in the final vmlinux, and enable orphan section warnings.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
 arch/x86/Makefile             | 4 ++++
 arch/x86/kernel/vmlinux.lds.S | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 00e378de8bc0..f8a5b2333729 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -51,6 +51,10 @@ ifdef CONFIG_X86_NEED_RELOCS
         LDFLAGS_vmlinux := --emit-relocs --discard-none
 endif
 
+# We never want expected sections to be placed heuristically by the
+# linker. All sections should be explicitly named in the linker script.
+LDFLAGS_vmlinux += --orphan-handling=warn
+
 #
 # Prevent GCC from generating any FP code by mistake.
 #
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 3bfc8dd8a43d..bb085ceeaaad 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -412,6 +412,12 @@ SECTIONS
 	DWARF_DEBUG
 
 	DISCARDS
+	/DISCARD/ : {
+		*(.rela.*) *(.rela_*)
+		*(.rel.*) *(.rel_*)
+		*(.got) *(.got.*)
+		*(.igot.*) *(.iplt)
+	}
 }
 
 
-- 
2.25.1

