arm64/build: Assert for unwanted sections

In preparation for warning on orphan sections, discard
unwanted non-zero-sized generated sections, and enforce other
expected-to-be-zero-sized sections (since discarding them might hide
problems with them suddenly gaining unexpected entries).

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200821194310.3089815-14-keescook@chromium.org

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 16eb2ef..e8847ca 100644 (file)
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -121,6 +121,14 @@ SECTIONS
                *(.got)                 /* Global offset table          */
        }
 
+       /*
+        * Make sure that the .got.plt is either completely empty or it
+        * contains only the lazy dispatch entries.
+        */
+       .got.plt : { *(.got.plt) }
+       ASSERT(SIZEOF(.got.plt) == 0 || SIZEOF(.got.plt) == 0x18,
+              "Unexpected GOT/PLT entries detected!")
+
        . = ALIGN(SEGMENT_ALIGN);
        _etext = .;                     /* End of text section */
 
@@ -243,6 +251,18 @@ SECTIONS
        ELF_DETAILS
 
        HEAD_SYMBOLS
+
+       /*
+        * Sections that should stay zero sized, which is safer to
+        * explicitly check instead of blindly discarding.
+        */
+       .plt : {
+               *(.plt) *(.plt.*) *(.iplt) *(.igot)
+       }
+       ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages detected!")
+
+       .data.rel.ro : { *(.data.rel.ro) }
+       ASSERT(SIZEOF(.data.rel.ro) == 0, "Unexpected RELRO detected!")
 }
 
 #include "image-vars.h"