[PATCH v2 04/17] module: ensure __cfi_check alignment

From: Sami Tolvanen <samitolvanen@google.com>
To: Kees Cook <keescook@chromium.org>
Cc: Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Will Deacon <will@kernel.org>, Jessica Yu <jeyu@kernel.org>,
	Arnd Bergmann <arnd@arndb.de>, Tejun Heo <tj@kernel.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	bpf@vger.kernel.org, linux-hardening@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kbuild@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Sami Tolvanen <samitolvanen@google.com>
Subject: [PATCH v2 04/17] module: ensure __cfi_check alignment
Date: Thu, 18 Mar 2021 10:10:58 -0700	[thread overview]
Message-ID: <20210318171111.706303-5-samitolvanen@google.com> (raw)
In-Reply-To: <20210318171111.706303-1-samitolvanen@google.com>

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@google.com>
---
 scripts/module.lds.S | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/scripts/module.lds.S b/scripts/module.lds.S
index 168cd27e6122..93518579cf5d 100644
--- a/scripts/module.lds.S
+++ b/scripts/module.lds.S
@@ -3,10 +3,19 @@
  * Archs are free to supply their own linker scripts.  ld will
  * combine them automatically.
  */
+#include <asm/page.h>
+
+#ifdef CONFIG_CFI_CLANG
+# define ALIGN_CFI ALIGN(PAGE_SIZE)
+#else
+# define ALIGN_CFI
+#endif
+
 SECTIONS {
 	/DISCARD/ : {
 		*(.discard)
 		*(.discard.*)
+		*(.eh_frame)
 	}
 
 	__ksymtab		0 : { *(SORT(___ksymtab+*)) }
@@ -40,7 +49,14 @@ 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*)
+	}
 }
 
 /* bring in arch-specific sections */
-- 
2.31.0.291.g576ba9dcdaf-goog

