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

[tip-bot2 for Kees Cook]

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@xxxxxxxxxxxx>
AuthorDate:    Fri, 21 Aug 2020 12:43:04 -07:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
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@xxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200821194310.3089815-24-keescook@xxxxxxxxxxxx
---
 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
 /*