From: Dave Gerlach <d-gerlach@ti.com>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Arnd Bergmann <arnd@arndb.de>, Tony Lindgren <tony@atomide.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <linux-omap@vger.kernel.org>,
Shawn Guo <shawnguo@kernel.org>,
Alexandre Belloni <alexandre.belloni@free-electrons.com>,
Keerthy J <j-keerthy@ti.com>
Subject: Re: [PATCH] misc: sram-exec: Use aligned fncpy instead of memcpy
Date: Thu, 6 Apr 2017 14:14:12 -0500 [thread overview]
Message-ID: <9a970ac7-cb8f-28f4-3b84-ad8bedf1242c@ti.com> (raw)
In-Reply-To: <20170406190747.GP23750@n2100.armlinux.org.uk>
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@ti.com>
>>> ---
>>> 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.
Regards,
Dave
WARNING: multiple messages have this Message-ID (diff)
From: Dave Gerlach <d-gerlach@ti.com>
To: Russell King - ARM Linux <linux@armlinux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>, Tony Lindgren <tony@atomide.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org,
Alexandre Belloni <alexandre.belloni@free-electrons.com>,
Keerthy J <j-keerthy@ti.com>,
linux-omap@vger.kernel.org, Shawn Guo <shawnguo@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] misc: sram-exec: Use aligned fncpy instead of memcpy
Date: Thu, 6 Apr 2017 14:14:12 -0500 [thread overview]
Message-ID: <9a970ac7-cb8f-28f4-3b84-ad8bedf1242c@ti.com> (raw)
In-Reply-To: <20170406190747.GP23750@n2100.armlinux.org.uk>
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@ti.com>
>>> ---
>>> 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.
Regards,
Dave
WARNING: multiple messages have this Message-ID (diff)
From: d-gerlach@ti.com (Dave Gerlach)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] misc: sram-exec: Use aligned fncpy instead of memcpy
Date: Thu, 6 Apr 2017 14:14:12 -0500 [thread overview]
Message-ID: <9a970ac7-cb8f-28f4-3b84-ad8bedf1242c@ti.com> (raw)
In-Reply-To: <20170406190747.GP23750@n2100.armlinux.org.uk>
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@ti.com>
>>> ---
>>> 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.
Regards,
Dave
next prev parent reply other threads:[~2017-04-06 19:15 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-05 19:21 [PATCH] misc: sram-exec: Use aligned fncpy instead of memcpy Dave Gerlach
2017-04-05 19:21 ` Dave Gerlach
2017-04-05 19:21 ` Dave Gerlach
2017-04-05 19:22 ` Dave Gerlach
2017-04-05 19:22 ` Dave Gerlach
2017-04-05 19:22 ` Dave Gerlach
2017-04-06 19:07 ` Russell King - ARM Linux
2017-04-06 19:07 ` Russell King - ARM Linux
2017-04-06 19:14 ` Dave Gerlach [this message]
2017-04-06 19:14 ` Dave Gerlach
2017-04-06 19:14 ` Dave Gerlach
2017-04-06 19:29 ` Russell King - ARM Linux
2017-04-06 19:29 ` Russell King - ARM Linux
2017-04-06 19:35 ` Dave Gerlach
2017-04-06 19:35 ` Dave Gerlach
2017-04-06 19:35 ` Dave Gerlach
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