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Date:   Wed, 13 Oct 2021 11:16:51 -0700
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Subject: [PATCH v5 08/15] lkdtm: Use an opaque type for lkdtm_rodata_do_nothing
From:   Sami Tolvanen <samitolvanen@google.com>
To:     x86@kernel.org
Cc:     Kees Cook <keescook@chromium.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Sedat Dilek <sedat.dilek@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        linux-hardening@vger.kernel.org, linux-kernel@vger.kernel.org,
        llvm@lists.linux.dev, Sami Tolvanen <samitolvanen@google.com>
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Use an opaque type for lkdtm_rodata_do_nothing to stop the compiler
from generating a CFI jump table entry that jumps to .rodata.

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Acked-by: Kees Cook <keescook@chromium.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
---
 drivers/misc/lkdtm/lkdtm.h  | 2 +-
 drivers/misc/lkdtm/perms.c  | 2 +-
 drivers/misc/lkdtm/rodata.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h
index c212a253edde..35535c422939 100644
--- a/drivers/misc/lkdtm/lkdtm.h
+++ b/drivers/misc/lkdtm/lkdtm.h
@@ -137,7 +137,7 @@ void lkdtm_REFCOUNT_TIMING(void);
 void lkdtm_ATOMIC_TIMING(void);
 
 /* rodata.c */
-void lkdtm_rodata_do_nothing(void);
+DECLARE_NOT_CALLED_FROM_C(lkdtm_rodata_do_nothing);
 
 /* usercopy.c */
 void __init lkdtm_usercopy_init(void);
diff --git a/drivers/misc/lkdtm/perms.c b/drivers/misc/lkdtm/perms.c
index 2dede2ef658f..fa2bd90bd8ee 100644
--- a/drivers/misc/lkdtm/perms.c
+++ b/drivers/misc/lkdtm/perms.c
@@ -151,7 +151,7 @@ void lkdtm_EXEC_VMALLOC(void)
 
 void lkdtm_EXEC_RODATA(void)
 {
-	execute_location(lkdtm_rodata_do_nothing, CODE_AS_IS);
+	execute_location((void *)lkdtm_rodata_do_nothing, CODE_AS_IS);
 }
 
 void lkdtm_EXEC_USERSPACE(void)
diff --git a/drivers/misc/lkdtm/rodata.c b/drivers/misc/lkdtm/rodata.c
index baacb876d1d9..17ed0ad4e6ae 100644
--- a/drivers/misc/lkdtm/rodata.c
+++ b/drivers/misc/lkdtm/rodata.c
@@ -3,7 +3,7 @@
  * This includes functions that are meant to live entirely in .rodata
  * (via objcopy tricks), to validate the non-executability of .rodata.
  */
-#include "lkdtm.h"
+void lkdtm_rodata_do_nothing(void);
 
 void noinstr lkdtm_rodata_do_nothing(void)
 {
-- 
2.33.0.1079.g6e70778dc9-goog