Russell,
On 04/05/2017 02:21 PM, Dave Gerlach wrote:
Currently the sram-exec functionality, which allows allocation of
executable memory and provides an API to move code to it, is only
selected in configs for the ARM architecture. Based on commit
5756e9dd0de6 ("ARM: 6640/1: Thumb-2: Symbol manipulation macros for
function body copying") simply copying a C function pointer address
using memcpy without consideration of alignment and Thumb is unsafe on
ARM platforms.
The aforementioned patch introduces the fncpy macro which is a safe way
to copy executable code on ARM platforms, so let's make use of that here
rather than the unsafe plain memcpy that was previously used by
sram_exec_copy.
In the future, architectures hoping to make use of the sram-exec
functionality must define an fncpy macro just as ARM has done to
guarantee or check for safe copying to executable memory before allowing
the arch to select CONFIG_SRAM_EXEC.
Signed-off-by: Dave Gerlach <d-gerlach@xxxxxx>
---
drivers/misc/sram-exec.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/misc/sram-exec.c b/drivers/misc/sram-exec.c
index ac522417c462..0057eabe5c03 100644
--- a/drivers/misc/sram-exec.c
+++ b/drivers/misc/sram-exec.c
@@ -19,6 +19,7 @@
#include <linux/sram.h>
#include <asm/cacheflush.h>
+#include <asm/fncpy.h>
#include "sram.h"
@@ -93,7 +94,7 @@ int sram_exec_copy(struct gen_pool *pool, void *dst, void *src,
set_memory_nx((unsigned long)base, pages);
set_memory_rw((unsigned long)base, pages);
- memcpy(dst, src, size);
+ fncpy(dst, src, size);
set_memory_ro((unsigned long)base, pages);
set_memory_x((unsigned long)base, pages);
Does this address your concerns from here [1]? Because the only user of this
code is ARM right now I already only build the sram-exec code in if CONFIG_ARM
is selected. I originally split the sram-exec code into its own file as it
already depends on the changes you made to set_memory_* APIs for ARM which we
have a hard dependency on here, and not all platforms support this. So this
allowed me to constrain the sram_exec code to platforms with the proper
set_memory_* APIs defined, but also now this lets us directly use the fncpy
macro in this driver. For future platforms that want to make use of sram_exec we
set the constraint that an arch must:
* Support the required set_memory_* APIs
* Define a fncpy macro that guarantees safe movement of a function.
This seems reasonable to me and gives support for ARM right away with a path
forward for additional architectures to support sram_exec.
Regards,
Dave
[1] https://www.spinics.net/lists/arm-kernel/msg574481.html
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