[PATCH v4 08/15] lkdtm: Use an opaque type for lkdtm_rodata_do_nothing

Sami Tolvanen
2021-09-30T18:06:03Z

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>
---
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..2da74236c005 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_ASM_FUNC_SYMBOL(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)
{
--
2.33.0.800.g4c38ced690-goog