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

Kees Cook
2020-07-31T23:08:56Z

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>
---
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