On 04/06/2017 02:29 PM, Russell King - ARM Linux wrote:
On Thu, Apr 06, 2017 at 02:14:12PM -0500, Dave Gerlach wrote:
On 04/06/2017 02:07 PM, Russell King - ARM Linux wrote:
On Wed, Apr 05, 2017 at 02:22:33PM -0500, Dave Gerlach wrote:
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.
Sorry, it does not. Please read the comments in asm/fncpy.h.
Deviating from the proscribed usage means your code is, quite simply,
buggy. There's no two ways about that.
I understand there are many constraints to using fncpy, as this is what we
used before to copy our executable code. Apart from users being aware of
what these constraints are (8-byte aligned, position independent) and making
sure the code they are moving meets them, are you saying we need some sort
of additional strict enforcement of them? Because fncpy today will throw a
bug if you fail to align src and dst properly, so adding another check will
just double the messages to the user.
Yes, fncpy() will throw a bug, but as I've already explained:
sram = alloc();
sram_func = fncpy(sram, func, func_size);
sram_func();
is the _only_ valid usage.
You must not do:
sram = alloc();
fncpy(sram, func, func_size);
sram();
because that will not work with Thumb code. The only permitted usage
is as per the first example above, everything else is buggy.
I see exactly what you mean now. I missed that before, thank you for clarifying.
Will update this patch and send a new version.
Regards,
Dave
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