linux-hardening - Re: [PATCH] platform/surface: Split memcpy() of struct ssam

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Date:   Tue, 27 Sep 2022 15:15:30 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Kees Cook <keescook@...omium.org>,
        Maximilian Luz <luzmaximilian@...il.com>
Cc:     Mark Gross <markgross@...nel.org>,
        platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] platform/surface: Split memcpy() of struct ssam_event
 flexible array

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@...il.com>
> Cc: Hans de Goede <hdegoede@...hat.com>
> Cc: Mark Gross <markgross@...nel.org>
> Cc: platform-driver-x86@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.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;