linux-kernel - [PATCH v2 mips-next 3/4] MIPS: vmlinux.lds.S: catch bad .got, .plt and .rel.dyn at link time

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Date:   Wed, 06 Jan 2021 20:08:29 +0000
From:   Alexander Lobakin <alobakin@...me>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     Alexander Lobakin <alobakin@...me>,
        Nathan Chancellor <natechancellor@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Fangrui Song <maskray@...gle.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Alex Smith <alex.smith@...tec.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Markos Chandras <markos.chandras@...tec.com>,
        linux-mips@...r.kernel.org, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 mips-next 3/4] MIPS: vmlinux.lds.S: catch bad .got, .plt and .rel.dyn at link time

Catch any symbols placed in .got, .got.plt, .plt, .rel.dyn
or .rela.dyn and check for these sections to be zero-sized
at link time.

At least two of them were noticed in real builds:

mips-alpine-linux-musl-ld: warning: orphan section `.rel.dyn'
from `init/main.o' being placed in section `.rel.dyn'

ld.lld: warning: <internal>:(.got) is being placed in '.got'

Adopted from x86/kernel/vmlinux.lds.S.

Reported-by: Nathan Chancellor <natechancellor@...il.com> # .got
Suggested-by: Fangrui Song <maskray@...gle.com> # .rel.dyn
Signed-off-by: Alexander Lobakin <alobakin@...me>
---
 arch/mips/kernel/vmlinux.lds.S | 35 ++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/arch/mips/kernel/vmlinux.lds.S b/arch/mips/kernel/vmlinux.lds.S
index 5d6563970ab2..05eda9d9a7d5 100644
--- a/arch/mips/kernel/vmlinux.lds.S
+++ b/arch/mips/kernel/vmlinux.lds.S
@@ -227,4 +227,39 @@ SECTIONS
 		*(.pdr)
 		*(.reginfo)
 	}
+
+	/*
+	 * Sections that should stay zero sized, which is safer to
+	 * explicitly check instead of blindly discarding.
+	 */
+
+	.got : {
+		*(.got)
+		*(.igot.*)
+	}
+	ASSERT(SIZEOF(.got) == 0, "Unexpected GOT entries detected!")
+
+	.got.plt (INFO) : {
+		*(.got.plt)
+	}
+	ASSERT(SIZEOF(.got.plt) == 0, "Unexpected GOT/PLT entries detected!")
+
+	.plt : {
+		*(.plt)
+		*(.plt.*)
+		*(.iplt)
+	}
+	ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
+
+	.rel.dyn : {
+		*(.rel.*)
+		*(.rel_*)
+	}
+	ASSERT(SIZEOF(.rel.dyn) == 0, "Unexpected run-time relocations (.rel) detected!")
+
+	.rela.dyn : {
+		*(.rela.*)
+		*(.rela_*)
+	}
+	ASSERT(SIZEOF(.rela.dyn) == 0, "Unexpected run-time relocations (.rela) detected!")
 }
-- 
2.30.0