[PATCH] HID: hyperv: avoid struct memcpy overrun warning

[PATCH] HID: hyperv: avoid struct memcpy overrun warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

A previous patch addressed the fortified memcpy warning for most
builds, but I still see this one with gcc-9:

In file included from include/linux/string.h:254,
                 from drivers/hid/hid-hyperv.c:8:
In function 'fortify_memcpy_chk',
    inlined from 'mousevsc_on_receive' at drivers/hid/hid-hyperv.c:272:3:
include/linux/fortify-string.h:583:4: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
  583 |    __write_overflow_field(p_size_field, size);
      |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

My guess is that the WARN_ON() itself is what confuses gcc, so it no
longer sees that there is a correct range check. Rework the code in a
way that helps readability and avoids the warning.

Fixes: 542f25a944715 ("HID: hyperv: Replace one-element array with flexible-array member")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/hid/hid-hyperv.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
index 49d4a26895e76..f33485d83d24f 100644
--- a/drivers/hid/hid-hyperv.c
+++ b/drivers/hid/hid-hyperv.c
@@ -258,19 +258,17 @@ static void mousevsc_on_receive(struct hv_device *device,
 
 	switch (hid_msg_hdr->type) {
 	case SYNTH_HID_PROTOCOL_RESPONSE:
+		len = struct_size(pipe_msg, data, pipe_msg->size);
+
 		/*
 		 * While it will be impossible for us to protect against
 		 * malicious/buggy hypervisor/host, add a check here to
 		 * ensure we don't corrupt memory.
 		 */
-		if (struct_size(pipe_msg, data, pipe_msg->size)
-			> sizeof(struct mousevsc_prt_msg)) {
-			WARN_ON(1);
+		if (WARN_ON(len > sizeof(struct mousevsc_prt_msg)))
 			break;
-		}
 
-		memcpy(&input_dev->protocol_resp, pipe_msg,
-				struct_size(pipe_msg, data, pipe_msg->size));
+		memcpy(&input_dev->protocol_resp, pipe_msg, len);
 		complete(&input_dev->wait_event);
 		break;
 
-- 
2.39.2

RE: [PATCH] HID: hyperv: avoid struct memcpy overrun warning

[Michael Kelley (LINUX)]

From: Arnd Bergmann <arnd@kernel.org> Sent: Wednesday, July 5, 2023 7:02 AM
> 
> A previous patch addressed the fortified memcpy warning for most
> builds, but I still see this one with gcc-9:
> 
> In file included from include/linux/string.h:254,
>                  from drivers/hid/hid-hyperv.c:8:
> In function 'fortify_memcpy_chk',
>     inlined from 'mousevsc_on_receive' at drivers/hid/hid-hyperv.c:272:3:
> include/linux/fortify-string.h:583:4: error: call to '__write_overflow_field' declared with
> attribute warning: detected write beyond size of field (1st parameter); maybe use
> struct_group()? [-Werror=attribute-warning]
>   583 |    __write_overflow_field(p_size_field, size);
>       |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> My guess is that the WARN_ON() itself is what confuses gcc, so it no
> longer sees that there is a correct range check. Rework the code in a
> way that helps readability and avoids the warning.
> 
> Fixes: 542f25a944715 ("HID: hyperv: Replace one-element array with flexible-array member")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/hid/hid-hyperv.c | 10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
> index 49d4a26895e76..f33485d83d24f 100644
> --- a/drivers/hid/hid-hyperv.c
> +++ b/drivers/hid/hid-hyperv.c
> @@ -258,19 +258,17 @@ static void mousevsc_on_receive(struct hv_device *device,
> 
>  	switch (hid_msg_hdr->type) {
>  	case SYNTH_HID_PROTOCOL_RESPONSE:
> +		len = struct_size(pipe_msg, data, pipe_msg->size);
> +
>  		/*
>  		 * While it will be impossible for us to protect against
>  		 * malicious/buggy hypervisor/host, add a check here to
>  		 * ensure we don't corrupt memory.
>  		 */
> -		if (struct_size(pipe_msg, data, pipe_msg->size)
> -			> sizeof(struct mousevsc_prt_msg)) {
> -			WARN_ON(1);
> +		if (WARN_ON(len > sizeof(struct mousevsc_prt_msg)))
>  			break;
> -		}
> 
> -		memcpy(&input_dev->protocol_resp, pipe_msg,
> -				struct_size(pipe_msg, data, pipe_msg->size));
> +		memcpy(&input_dev->protocol_resp, pipe_msg, len);
>  		complete(&input_dev->wait_event);
>  		break;
> 
> --
> 2.39.2

Reviewed-by: Michael Kelley <mikelley@microsoft.com>

Re: [PATCH] HID: hyperv: avoid struct memcpy overrun warning

[Benjamin Tissoires]

On Wed, 05 Jul 2023 16:02:24 +0200, Arnd Bergmann wrote:
> A previous patch addressed the fortified memcpy warning for most
> builds, but I still see this one with gcc-9:
> 
> In file included from include/linux/string.h:254,
>                  from drivers/hid/hid-hyperv.c:8:
> In function 'fortify_memcpy_chk',
>     inlined from 'mousevsc_on_receive' at drivers/hid/hid-hyperv.c:272:3:
> include/linux/fortify-string.h:583:4: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
>   583 |    __write_overflow_field(p_size_field, size);
>       |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> [...]

Applied to https://git.kernel.org/pub/scm/linux/kernel/git/hid/hid.git (for-6.5/upstream-fixes), thanks!

[1/1] HID: hyperv: avoid struct memcpy overrun warning
      https://git.kernel.org/hid/hid/c/5f151364b1da

Cheers,
-- 
Benjamin Tissoires <bentiss@kernel.org>

Re: [PATCH] HID: hyperv: avoid struct memcpy overrun warning

[Andy Shevchenko]

On Wed, Jul 05, 2023 at 04:02:24PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> A previous patch addressed the fortified memcpy warning for most
> builds, but I still see this one with gcc-9:

JFYI: as of today I have run Linux Next with `make W=1 allmodconfig` on x86_64
and it seems there are still tons of similar issues which break the build.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH] HID: hyperv: avoid struct memcpy overrun warning

[Arnd Bergmann]

On Mon, Jul 17, 2023, at 11:36, Andy Shevchenko wrote:
> On Wed, Jul 05, 2023 at 04:02:24PM +0200, Arnd Bergmann wrote:
>> From: Arnd Bergmann <arnd@arndb.de>
>> 
>> A previous patch addressed the fortified memcpy warning for most
>> builds, but I still see this one with gcc-9:
>
> JFYI: as of today I have run Linux Next with `make W=1 allmodconfig` on x86_64
> and it seems there are still tons of similar issues which break the build.

It's a bit more complex:

- yes, there are lots of warnings for memcpy() read overflow when you
  build allmodconfig kernels with W=1. I have patches for all of these and
  plan to submit them over time.

- This particular one is a memcpy /write/ overflow, i.e. the
  destination type overflows with the length according to gcc's
  understanding of the structures. This warning is enabled even
  without W=1, though it may only show up in certain configurations
  or compiler versions.

      Arnd