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@chromium.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200821194310.3089815-24-keescook@chromium.org

diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 0cc035c..4b1b936 100644 (file)
--- 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
 /*