[PATCH] platform/surface: Split memcpy() of struct ssam_event flexible array

[PATCH] platform/surface: Split memcpy() of struct ssam_event flexible array

[Kees Cook]

To work around a misbehavior of the compiler's ability to see into
composite flexible array structs (as detailed in the coming memcpy()
hardening series[1]), split the memcpy() of the header and the payload
so no false positive run-time overflow warning will be generated.

[1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org

Cc: Maximilian Luz <luzmaximilian@gmail.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Mark Gross <markgross@kernel.org>
Cc: platform-driver-x86@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
 drivers/platform/surface/surface_acpi_notify.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/platform/surface/surface_acpi_notify.c b/drivers/platform/surface/surface_acpi_notify.c
index 44e317970557..50500e562963 100644
--- a/drivers/platform/surface/surface_acpi_notify.c
+++ b/drivers/platform/surface/surface_acpi_notify.c
@@ -355,7 +355,8 @@ static u32 san_evt_bat_nf(struct ssam_event_notifier *nf,
 	INIT_DELAYED_WORK(&work->work, san_evt_bat_workfn);
 	work->dev = d->dev;
 
-	memcpy(&work->event, event, sizeof(struct ssam_event) + event->length);
+	work->event = *event;
+	memcpy(work->event.data, event->data, event->length);
 
 	queue_delayed_work(san_wq, &work->work, delay);
 	return SSAM_NOTIF_HANDLED;
-- 
2.34.1

Re: [PATCH] platform/surface: Split memcpy() of struct ssam_event flexible array

[Gustavo A. R. Silva]

On Mon, Sep 26, 2022 at 05:40:11PM -0700, Kees Cook wrote:
> To work around a misbehavior of the compiler's ability to see into
> composite flexible array structs (as detailed in the coming memcpy()
> hardening series[1]), split the memcpy() of the header and the payload
> so no false positive run-time overflow warning will be generated.
> 
> [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org
> 
> Cc: Maximilian Luz <luzmaximilian@gmail.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Mark Gross <markgross@kernel.org>
> Cc: platform-driver-x86@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
--
Gustavo

> ---
>  drivers/platform/surface/surface_acpi_notify.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/surface/surface_acpi_notify.c b/drivers/platform/surface/surface_acpi_notify.c
> index 44e317970557..50500e562963 100644
> --- a/drivers/platform/surface/surface_acpi_notify.c
> +++ b/drivers/platform/surface/surface_acpi_notify.c
> @@ -355,7 +355,8 @@ static u32 san_evt_bat_nf(struct ssam_event_notifier *nf,
>  	INIT_DELAYED_WORK(&work->work, san_evt_bat_workfn);
>  	work->dev = d->dev;
>  
> -	memcpy(&work->event, event, sizeof(struct ssam_event) + event->length);
> +	work->event = *event;
> +	memcpy(work->event.data, event->data, event->length);
>  
>  	queue_delayed_work(san_wq, &work->work, delay);
>  	return SSAM_NOTIF_HANDLED;
> -- 
> 2.34.1
> 

Re: [PATCH] platform/surface: Split memcpy() of struct ssam_event flexible array

[Maximilian Luz]

On 9/27/22 02:40, Kees Cook wrote:
> To work around a misbehavior of the compiler's ability to see into
> composite flexible array structs (as detailed in the coming memcpy()
> hardening series[1]), split the memcpy() of the header and the payload
> so no false positive run-time overflow warning will be generated.
> 
> [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org
> 
> Cc: Maximilian Luz <luzmaximilian@gmail.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Mark Gross <markgross@kernel.org>
> Cc: platform-driver-x86@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thanks!

Reviewed-by: Maximilian Luz <luzmaximilian@gmail.com>

Regards,
Max

> ---
>   drivers/platform/surface/surface_acpi_notify.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/surface/surface_acpi_notify.c b/drivers/platform/surface/surface_acpi_notify.c
> index 44e317970557..50500e562963 100644
> --- a/drivers/platform/surface/surface_acpi_notify.c
> +++ b/drivers/platform/surface/surface_acpi_notify.c
> @@ -355,7 +355,8 @@ static u32 san_evt_bat_nf(struct ssam_event_notifier *nf,
>   	INIT_DELAYED_WORK(&work->work, san_evt_bat_workfn);
>   	work->dev = d->dev;
>   
> -	memcpy(&work->event, event, sizeof(struct ssam_event) + event->length);
> +	work->event = *event;
> +	memcpy(work->event.data, event->data, event->length);
>   
>   	queue_delayed_work(san_wq, &work->work, delay);
>   	return SSAM_NOTIF_HANDLED;

Re: [PATCH] platform/surface: Split memcpy() of struct ssam_event flexible array

[Hans de Goede]

Hi,

On 9/27/22 02:40, Kees Cook wrote:
> To work around a misbehavior of the compiler's ability to see into
> composite flexible array structs (as detailed in the coming memcpy()
> hardening series[1]), split the memcpy() of the header and the payload
> so no false positive run-time overflow warning will be generated.
> 
> [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org
> 
> Cc: Maximilian Luz <luzmaximilian@gmail.com>
> Cc: Hans de Goede <hdegoede@redhat.com>
> Cc: Mark Gross <markgross@kernel.org>
> Cc: platform-driver-x86@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Thank you for your patch, I've applied this patch to my review-hans 
branch:
https://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86.git/log/?h=review-hans

Note it will show up in my review-hans branch once I've pushed my
local branch there, which might take a while.

Once I've run some tests on this branch the patches there will be
added to the platform-drivers-x86/for-next branch and eventually
will be included in the pdx86 pull-request to Linus for the next
merge-window.

Regards,

Hans

> ---
>  drivers/platform/surface/surface_acpi_notify.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/surface/surface_acpi_notify.c b/drivers/platform/surface/surface_acpi_notify.c
> index 44e317970557..50500e562963 100644
> --- a/drivers/platform/surface/surface_acpi_notify.c
> +++ b/drivers/platform/surface/surface_acpi_notify.c
> @@ -355,7 +355,8 @@ static u32 san_evt_bat_nf(struct ssam_event_notifier *nf,
>  	INIT_DELAYED_WORK(&work->work, san_evt_bat_workfn);
>  	work->dev = d->dev;
>  
> -	memcpy(&work->event, event, sizeof(struct ssam_event) + event->length);
> +	work->event = *event;
> +	memcpy(work->event.data, event->data, event->length);
>  
>  	queue_delayed_work(san_wq, &work->work, delay);
>  	return SSAM_NOTIF_HANDLED;