[PATCH v4 17/17] x86/boot: Warn on orphan section placement

Kees Cook
2020-06-29T06:18:40Z

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 | 10 ++++++++++
2 files changed, 12 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 d88612e3091f..9afb8737896f 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -75,7 +75,17 @@ SECTIONS
. = ALIGN(PAGE_SIZE); /* keep ZO size page aligned */
_end = .;

+ STABS_DEBUG
+ DWARF_DEBUG
ELF_DETAILS

DISCARDS
+ /DISCARD/ : {
+ *(.note.*)
+ *(.rela.*) *(.rela_*)
+ *(.rel.*) *(.rel_*)
+ *(.plt) *(.plt.*)
+ *(.dyn*)
+ *(.hash) *(.gnu.hash)
+ }
}
--
2.25.1