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Date: Wed, 3 Aug 2016 14:59:31 +1000
From: Michael Ellerman <mpe@...erman.id.au>
To: Kees Cook <keescook@...omium.org>
Cc: <linuxppc-dev@...abs.org>,
<linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...l.org>,
Greg Kroah-Hartman <greg@...ah.com>,
kernel-hardening@...ts.openwall.com,
Anton Blanchard <anton@...ba.org>,
<amodra@...il.com>,
Nick Piggin <npiggin@...il.com>
Subject: [PATCH] lkdtm: Mark lkdtm_rodata_do_nothing() notrace
lkdtm_rodata_do_nothing() is an empty function which is generated in
order to test the non-executability of rodata.
Currently if function tracing is enabled then an mcount callsite will be
generated for lkdtm_rodata_do_nothing(), and it will appear in the list
of available functions for function tracing (available_filter_functions).
Given it's purpose purely as a test function, it seems preferable for
lkdtm_rodata_do_nothing() to be marked notrace, so it doesn't appear as
traceable.
This also avoids triggering a linker bug on powerpc:
https://sourceware.org/bugzilla/show_bug.cgi?id=20428
When the linker sees code that needs to generate a call stub, eg. a
branch to mcount(), it assumes the section is executable and
dereferences a NULL pointer leading to a linker segfault. Marking
lkdtm_rodata_do_nothing() notrace avoids triggering the bug because the
function contains no other function calls.
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
---
drivers/misc/lkdtm_rodata.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/misc/lkdtm_rodata.c b/drivers/misc/lkdtm_rodata.c
index 166b1db3969f..3564477b8c2d 100644
--- a/drivers/misc/lkdtm_rodata.c
+++ b/drivers/misc/lkdtm_rodata.c
@@ -4,7 +4,7 @@
*/
#include "lkdtm.h"
-void lkdtm_rodata_do_nothing(void)
+void notrace lkdtm_rodata_do_nothing(void)
{
/* Does nothing. We just want an architecture agnostic "return". */
}
--
2.7.4
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