linux-kernel - [PATCH v6 27/29] x86/boot/compressed: Remove, discard, or assert for unwanted sections

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Date:   Fri, 21 Aug 2020 12:43:08 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Peter Collingbourne <pcc@...gle.com>,
        James Morse <james.morse@....com>,
        Borislav Petkov <bp@...e.de>, Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Arnd Bergmann <arnd@...db.de>, x86@...nel.org,
        clang-built-linux@...glegroups.com, linux-arch@...r.kernel.org,
        linux-efi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v6 27/29] 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@...omium.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 753d57266757..5b7f6e175b03 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/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)
diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index ca544a16724b..02f6feb0e55b 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/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!")
 }
-- 
2.25.1