linux-kernel - [PATCH 7/9] arm64/build: Warn on orphan section placement

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Date:   Thu, 27 Feb 2020 16:22:42 -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 7/9] arm64/build: 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.

Explicitly include debug sections when they're present. Add .eh_frame*
to discard as it seems that these are still generated even though
-fno-asynchronous-unwind-tables is being specified. Add .plt and
.data.rel.ro to discards as they are not actually used. Add .got.plt
to the image as it does appear to be mapped near .data. Finally enable
orphan section warnings.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm64/Makefile             | 4 ++++
 arch/arm64/kernel/vmlinux.lds.S | 5 ++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
index dca1a97751ab..c682a65b3ab8 100644
--- a/arch/arm64/Makefile
+++ b/arch/arm64/Makefile
@@ -30,6 +30,10 @@ LDFLAGS_vmlinux	+= --fix-cortex-a53-843419
   endif
 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
+
 ifeq ($(CONFIG_ARM64_USE_LSE_ATOMICS), y)
   ifneq ($(CONFIG_ARM64_LSE_ATOMICS), y)
 $(warning LSE atomics not supported by binutils)
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index c61d9ab3211c..6141d5b72f8f 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -98,7 +98,8 @@ SECTIONS
 	/DISCARD/ : {
 		*(.interp .dynamic)
 		*(.dynsym .dynstr .hash .gnu.hash)
-		*(.eh_frame)
+		*(.plt) *(.data.rel.ro)
+		*(.eh_frame) *(.init.eh_frame)
 	}
 
 	. = KIMAGE_VADDR + TEXT_OFFSET;
@@ -212,6 +213,7 @@ SECTIONS
 	_data = .;
 	_sdata = .;
 	RW_DATA(L1_CACHE_BYTES, PAGE_SIZE, THREAD_ALIGN)
+	.got.plt : ALIGN(8) { *(.got.plt) }
 
 	/*
 	 * Data written with the MMU off but read with the MMU on requires
@@ -246,6 +248,7 @@ SECTIONS
 	_end = .;
 
 	STABS_DEBUG
+	DWARF_DEBUG
 
 	HEAD_SYMBOLS
 }
-- 
2.20.1