[PATCH v5 20/36] arm64/build: Assert for unwanted sections

[Kees Cook]

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 <a...@kernel.org>
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 arch/arm64/kernel/vmlinux.lds.S | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 4cf825301c3a..01485941ed35 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -122,6 +122,14 @@ 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 */
 
@@ -244,6 +252,18 @@ SECTIONS
        ELF_DETAILS
 
        HEAD_SYMBOLS
+
+       /*
+        * Sections that should stay zero sized, which is safer to
+        * explicitly check instead of blindly discarding.
+        */
+       .plt (NOLOAD) : {
+               *(.plt) *(.plt.*) *(.iplt) *(.igot)
+       }
+       ASSERT(SIZEOF(.plt) == 0, "Unexpected run-time procedure linkages 
detected!")
+
+       .data.rel.ro (NOLOAD) : { *(.data.rel.ro) }
+       ASSERT(SIZEOF(.data.rel.ro) == 0, "Unexpected RELRO detected!")
 }
 
 #include "image-vars.h"
-- 
2.25.1