linux-kernel - [tip: core/build] x86/build: Enforce an empty .got.plt section

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Message-ID: <159896087384.20229.7620654432209669942.tip-bot2@tip-bot2>
Date:   Tue, 01 Sep 2020 11:47:53 -0000
From:   "tip-bot2 for Kees Cook" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...nel.org>,
        x86 <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [tip: core/build] x86/build: Enforce an empty .got.plt section

The following commit has been merged into the core/build branch of tip:

Commit-ID:     815d680771ae09080d2da83dac2647c08cdf99ce
Gitweb:        https://git.kernel.org/tip/815d680771ae09080d2da83dac2647c08cdf99ce
Author:        Kees Cook <keescook@...omium.org>
AuthorDate:    Fri, 21 Aug 2020 12:43:04 -07:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 01 Sep 2020 10:03:18 +02:00

x86/build: Enforce an empty .got.plt section

The .got.plt section should always be zero (or filled only with the
linker-generated lazy dispatch entry). Enforce this with an assert and
mark the section as INFO. This is more sensitive than just blindly
discarding the section.

Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/20200821194310.3089815-24-keescook@chromium.org
---
 arch/x86/kernel/vmlinux.lds.S | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 0cc035c..4b1b936 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -414,8 +414,20 @@ SECTIONS
 	ELF_DETAILS
 
 	DISCARDS
-}
 
+	/*
+	 * Make sure that the .got.plt is either completely empty or it
+	 * contains only the lazy dispatch entries.
+	 */
+	.got.plt (INFO) : { *(.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!")
+}
 
 #ifdef CONFIG_X86_32
 /*