[PATCH v6 04/18] module: ensure __cfi_check alignment

[Sami Tolvanen]

CONFIG_CFI_CLANG_SHADOW assumes the __cfi_check() function is page
aligned and at the beginning of the .text section. While Clang would
normally align the function correctly, it fails to do so for modules
with no executable code.

This change ensures the correct __cfi_check() location and
alignment. It also discards the .eh_frame section, which Clang can
generate with certain sanitizers, such as CFI.

Link: https://bugs.llvm.org/show_bug.cgi?id=46293
Signed-off-by: Sami Tolvanen <samitolvanen at google.com>
Reviewed-by: Kees Cook <keescook at chromium.org>
Acked-by: Jessica Yu <jeyu at kernel.org>
Tested-by: Nathan Chancellor <nathan at kernel.org>
---
 scripts/module.lds.S | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 2c52535f9b56..04c5685c25cf 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -3,10 +3,20 @@
  * Archs are free to supply their own linker scripts.  ld will
  * combine them automatically.
  */
+#ifdef CONFIG_CFI_CLANG
+# include <asm/page.h>
+# define ALIGN_CFI 		ALIGN(PAGE_SIZE)
+# define SANITIZER_DISCARDS	*(.eh_frame)
+#else
+# define ALIGN_CFI
+# define SANITIZER_DISCARDS
+#endif
+
 SECTIONS {
 	/DISCARD/ : {
 		*(.discard)
 		*(.discard.*)
+		SANITIZER_DISCARDS
 	}
 
 	__ksymtab		0 : { *(SORT(___ksymtab+*)) }
@@ -41,7 +51,14 @@ SECTIONS {
 		*(.rodata..L*)
 	}
 
-	.text : { *(.text .text.[0-9a-zA-Z_]*) }
+	/*
+	 * With CONFIG_CFI_CLANG, we assume __cfi_check is at the beginning
+	 * of the .text section, and is aligned to PAGE_SIZE.
+	 */
+	.text : ALIGN_CFI {
+		*(.text.__cfi_check)
+		*(.text .text.[0-9a-zA-Z_]* .text..L.cfi*)
+	}
 #endif
 }
 
-- 
2.31.1.295.g9ea45b61b8-goog