linux-kernel - [PATCH v6 13/29] arm64/build: Assert for unwanted sections

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Date:   Fri, 21 Aug 2020 12:42:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        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 13/29] arm64/build: Assert for unwanted sections

In preparation for warning on orphan 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).

Suggested-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/arm64/kernel/vmlinux.lds.S | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 16eb2ef806cd..6ccf19fd2b39 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -121,6 +121,14 @@ SECTIONS
 		*(.got)			/* Global offset table		*/
 	}
 
+	/*
+	 * Make sure that the .got.plt is either completely empty or it
+	 * contains only the lazy dispatch entries.
+	 */
+	.got.plt : { *(.got.plt) }
+	ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18,
+	       "Unexpected GOT/PLT entries detected!")
+
 	. = ALIGN(SEGMENT_ALIGN);
 	_etext = .;			/* End of text section */
 
@@ -243,6 +251,18 @@ SECTIONS
 	ELF_DETAILS
 
 	HEAD_SYMBOLS
+
+	/*
+	 * Sections that should stay zero sized, which is safer to
+	 * explicitly check instead of blindly discarding.
+	 */
+	.plt : {
+		*(.plt) *(.plt.*) *(.iplt) *(.igot)
+	}
+	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
+
+	.data.rel.ro : { *(.data.rel.ro) }
+	ASSERT(SIZEOF(.data.rel.ro) == 0, "Unexpected RELRO detected!")
 }
 
 #include "image-vars.h"
-- 
2.25.1