linux-kernel - [PATCH 4/9] x86/boot: Warn on orphan section placement

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Message-Id: <20200228002244.15240-5-keescook@chromium.org>
Date:   Thu, 27 Feb 2020 16:22:39 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Borislav Petkov <bp@...e.de>
Cc:     Kees Cook <keescook@...omium.org>, "H.J. Lu" <hjl.tools@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Peter Collingbourne <pcc@...gle.com>,
        James Morse <james.morse@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>, x86@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kbuild@...r.kernel.org, clang-built-linux@...glegroups.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 4/9] x86/boot: Warn on orphan section placement

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.

Add the common debugging sections. Discard the unused note, rel, plt,
dyn, and hash sections that are not needed in the compressed vmlinux.
Disable .eh_frame generation in the linker and enable orphan section
warnings.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/boot/compressed/Makefile      |  3 ++-
 arch/x86/boot/compressed/vmlinux.lds.S | 13 +++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index c33111341325..e0ea6b0924e8 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -46,6 +46,7 @@ GCOV_PROFILE := n
 UBSAN_SANITIZE :=n
 
 KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
+KBUILD_LDFLAGS += --no-ld-generated-unwind-info
 # Compressed kernel should be built as PIE since it may be loaded at any
 # address by the bootloader.
 ifeq ($(CONFIG_X86_32),y)
@@ -57,7 +58,7 @@ else
 KBUILD_LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \
 	&& echo "-z noreloc-overflow -pie --no-dynamic-linker")
 endif
-LDFLAGS_vmlinux := -T
+LDFLAGS_vmlinux := --orphan-handling=warn -T
 
 hostprogs	:= mkpiggy
 HOST_EXTRACFLAGS += -I$(srctree)/tools/include
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 508cfa6828c5..b5406a8cebe0 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -73,4 +73,17 @@ SECTIONS
 #endif
 	. = ALIGN(PAGE_SIZE);	/* keep ZO size page aligned */
 	_end = .;
+
+	STABS_DEBUG
+	DWARF_DEBUG
+
+	DISCARDS
+	/DISCARD/ : {
+		*(.note.*)
+		*(.rela.*) *(.rela_*)
+		*(.rel.*) *(.rel_*)
+		*(.plt) *(.plt.*)
+		*(.dyn*)
+		*(.hash) *(.gnu.hash)
+	}
 }
-- 
2.20.1