[PATCH v5 33/36] x86/boot/compressed: Remove, discard, or assert for unwanted sections

Kees Cook
2020-07-31T23:09:13Z

In preparation for warning on orphan sections, stop the linker from
generating the .eh_frame* sections, discard unwanted non-zero-sized
generated sections, and enforce other expected-to-be-zero-sized sections
(since discarding them might hide problems with them suddenly gaining
unexpected entries).

Signed-off-by: Kees Cook <keescook@chromium.org>
---
arch/x86/boot/compressed/Makefile | 1 +
arch/x86/boot/compressed/vmlinux.lds.S | 14 ++++++++++++--
2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 96d53e300ab6..43b49e1f5b6d 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -49,6 +49,7 @@ 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.
LDFLAGS_vmlinux := -pie $(call ld-option, --no-dynamic-linker)
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 42dea70a5091..1fb9809a9e61 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -83,6 +83,11 @@ SECTIONS
ELF_DETAILS

DISCARDS
+ /DISCARD/ : {
+ *(.dynamic) *(.dynsym) *(.dynstr) *(.dynbss)
+ *(.hash) *(.gnu.hash)
+ *(.note.*)
+ }

/*
* Sections that should stay zero sized, which is safer to
@@ -93,13 +98,18 @@ SECTIONS
}
ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")

+ .plt (NOLOAD) : {
+ *(.plt) *(.plt.*)
+ }
+ ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
+
/* ld.lld does not like .rel* sections being made "NOLOAD". */
.rel.dyn : {
- *(.rel.*)
+ *(.rel.*) *(.rel_*)
}
ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
.rela.dyn : {
- *(.rela.*)
+ *(.rela.*) *(.rela_*)
}
ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
}
--
2.25.1