x86/boot/compressed: Remove, discard, or assert for unwanted sections

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>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200821194310.3089815-28-keescook@chromium.org

arch/x86/boot/compressed/Makefile

@@ -50,6 +50,7 @@ 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)

arch/x86/boot/compressed/vmlinux.lds.S

@@ -72,6 +72,11 @@ SECTIONS
 	ELF_DETAILS
 
 	DISCARDS
+	/DISCARD/ : {
+		*(.dynamic) *(.dynsym) *(.dynstr) *(.dynbss)
+		*(.hash) *(.gnu.hash)
+		*(.note.*)
+	}
 
 	.got.plt (INFO) : {
 		*(.got.plt)
@@ -93,13 +98,18 @@ SECTIONS
 	}
 	ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
 
+	.plt : {
+		*(.plt) *(.plt.*)
+	}
+	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
+
 	.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!")
 }