Virtualization - Sep 2023 - [PATCH] virtio_console: Annotate struct port_buffer with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct port_buffer.

[1]
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Amit Shah <amit at kernel.org>
Cc: Arnd Bergmann <arnd at arndb.de>
Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Cc: virtualization at lists.linux-foundation.org
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 drivers/char/virtio_console.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 680d1ef2a217..431e9e5bf9c1 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -106,7 +106,7 @@ struct port_buffer {
 	unsigned int sgpages;
 
 	/* sg is used if spages > 0. sg must be the last in is struct */
-	struct scatterlist sg[];
+	struct scatterlist sg[] __counted_by(sgpages);
 };
 
 /*
-- 
2.34.1

On 9/22/23 11:51, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct port_buffer.
> 
> [1]
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Amit Shah <amit at kernel.org>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Cc: virtualization at lists.linux-foundation.org
> Signed-off-by: Kees Cook <keescook at chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars at kernel.org>

Thanks
-- 
Gustavo
> ---
>   drivers/char/virtio_console.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 680d1ef2a217..431e9e5bf9c1 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -106,7 +106,7 @@ struct port_buffer {
>   	unsigned int sgpages;
>   
>   	/* sg is used if spages > 0. sg must be the last in is struct */
> -	struct scatterlist sg[];
> +	struct scatterlist sg[] __counted_by(sgpages);
>   };
>   
>   /*

On Fri, 2023-09-22 at 10:51 -0700, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct port_buffer.
> 
> [1]
https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> Cc: Amit Shah <amit at kernel.org>
> Cc: Arnd Bergmann <arnd at arndb.de>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Cc: virtualization at lists.linux-foundation.org
> Signed-off-by: Kees Cook <keescook at chromium.org>
> ---
>  drivers/char/virtio_console.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index 680d1ef2a217..431e9e5bf9c1 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -106,7 +106,7 @@ struct port_buffer {
>  	unsigned int sgpages;
>  
>  	/* sg is used if spages > 0. sg must be the last in is struct */
> -	struct scatterlist sg[];
> +	struct scatterlist sg[] __counted_by(sgpages);
>  };
Reviewed-by: Amit Shah <amit at kernel.org>

Greg, please pick this up.

Thanks,

		Amit

On Fri, 22 Sep 2023 10:51:15 -0700, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct port_buffer.
> 
> [...]
Applied to for-next/hardening, thanks!

[1/1] virtio_console: Annotate struct port_buffer with __counted_by
      https://git.kernel.org/kees/c/bf5abc17bc43

Take care,

-- 
Kees Cook