[PATCH v3 5/9] x86/boot: Warn on orphan section placement

From: Kees Cook <keescook@chromium.org>
To: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	linux-arch@vger.kernel.org, linux-efi@vger.kernel.org,
	Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	x86@kernel.org, Nick Desaulniers <ndesaulniers@google.com>,
	Russell King <linux@armlinux.org.uk>,
	linux-kernel@vger.kernel.org,
	Nathan Chancellor <natechancellor@gmail.com>,
	clang-built-linux@googlegroups.com,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Ingo Molnar <mingo@redhat.com>, James Morse <james.morse@arm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@suse.de>,
	Peter Collingbourne <pcc@google.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: [PATCH v3 5/9] x86/boot: Warn on orphan section placement
Date: Tue, 23 Jun 2020 18:49:36 -0700	[thread overview]
Message-ID: <20200624014940.1204448-6-keescook@chromium.org> (raw)
In-Reply-To: <20200624014940.1204448-1-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.

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@chromium.org>
---
 arch/x86/boot/compressed/Makefile      |  3 ++-
 arch/x86/boot/compressed/vmlinux.lds.S | 11 +++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 7619742f91c9..646720a05f89 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -48,6 +48,7 @@ GCOV_PROFILE := n
 UBSAN_SANITIZE :=n
 
 KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
+KBUILD_LDFLAGS += $(call ld-option,--no-ld-generated-unwind-info)
 # Compressed kernel should be built as PIE since it may be loaded at any
 # address by the bootloader.
 ifeq ($(CONFIG_X86_32),y)
@@ -59,7 +60,7 @@ 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 8f1025d1f681..6fe3ecdfd685 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -75,5 +75,16 @@ SECTIONS
 	. = 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)
+	}
 }
-- 
2.25.1


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