linux-kernel - [PATCH v5 32/36] x86/boot/compressed: Reorganize zero-size section asserts

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Message-Id: <20200731230820.1742553-33-keescook@chromium.org>
Date:   Fri, 31 Jul 2020 16:08:16 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Gleixner <tglx@...utronix.de>, Will Deacon <will@...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 v5 32/36] x86/boot/compressed: Reorganize zero-size section asserts

For readability, move the zero-sized sections to the end after DISCARDS
and mark them NOLOAD for good measure.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/x86/boot/compressed/vmlinux.lds.S | 42 +++++++++++++++-----------
 1 file changed, 25 insertions(+), 17 deletions(-)

diff --git a/arch/x86/boot/compressed/vmlinux.lds.S b/arch/x86/boot/compressed/vmlinux.lds.S
index 3c2ee9a5bf43..42dea70a5091 100644
--- a/arch/x86/boot/compressed/vmlinux.lds.S
+++ b/arch/x86/boot/compressed/vmlinux.lds.S
@@ -42,18 +42,16 @@ SECTIONS
 		*(.rodata.*)
 		_erodata = . ;
 	}
-	.rel.dyn : {
-		*(.rel.*)
-	}
-	.rela.dyn : {
-		*(.rela.*)
-	}
-	.got : {
-		*(.got)
-	}
 	.got.plt : {
 		*(.got.plt)
 	}
+	ASSERT(SIZEOF(.got.plt) == 0 ||
+#ifdef CONFIG_X86_64
+	       SIZEOF(.got.plt) == 0x18,
+#else
+	       SIZEOF(.got.plt) == 0xc,
+#endif
+	       "Unexpected GOT/PLT entries detected!")
 
 	.data :	{
 		_data = . ;
@@ -85,13 +83,23 @@ SECTIONS
 	ELF_DETAILS
 
 	DISCARDS
-}
 
-ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
-#ifdef CONFIG_X86_64
-ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18, "Unexpected GOT/PLT entries detected!")
-#else
-ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0xc, "Unexpected GOT/PLT entries detected!")
-#endif
+	/*
+	 * Sections that should stay zero sized, which is safer to
+	 * explicitly check instead of blindly discarding.
+	 */
+	.got (NOLOAD) : {
+		*(.got)
+	}
+	ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
 
-ASSERT(SIZEOF(.rel.dyn) == 0 && SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations detected!")
+	/* ld.lld does not like .rel* sections being made "NOLOAD". */
+	.rel.dyn : {
+		*(.rel.*)
+	}
+	ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
+	.rela.dyn : {
+		*(.rela.*)
+	}
+	ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
+}
-- 
2.25.1