linux-kernel - Re: [PATCH 1/3] dell-laptop: Clear buffer before each SMBIOS call

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Date:	Wed, 1 Jul 2015 17:45:44 -0700
From:	Darren Hart <dvhart@...radead.org>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org,
	Gabriele Mazzotta <gabriele.mzt@...il.com>
Subject: Re: [PATCH 1/3] dell-laptop: Clear buffer before each SMBIOS call

On Wed, Jul 01, 2015 at 08:08:19PM +0200, Pali Rohár wrote:
> Make sure that before initializing SMBIOS call input buffer does not contain
> any garbage (e.g values from previous SMBIOS call). This fix problem with
> passing undefined/random parameters to SMBIOS functions.
> 
> Signed-off-by: Pali Rohár <pali.rohar@...il.com>
> ---
>  drivers/platform/x86/dell-laptop.c |   11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/x86/dell-laptop.c b/drivers/platform/x86/dell-laptop.c
> index 35758cb..6728487 100644
> --- a/drivers/platform/x86/dell-laptop.c
> +++ b/drivers/platform/x86/dell-laptop.c
> @@ -310,10 +310,15 @@ static DEFINE_MUTEX(buffer_mutex);
>  
>  static int hwswitch_state;
>  
> +static void clear_buffer(void)
> +{
> +	memset(buffer, 0, sizeof(struct calling_interface_buffer));
> +}
> +
>  static void get_buffer(void)
>  {
>  	mutex_lock(&buffer_mutex);
> -	memset(buffer, 0, sizeof(struct calling_interface_buffer));
> +	clear_buffer();
>  }
>  
>  static void release_buffer(void)
> @@ -557,6 +562,8 @@ static int dell_rfkill_set(void *data, bool blocked)
>  	    !(buffer->output[1] & BIT(16)))
>  		disable = 1;
>  
> +	clear_buffer();
> +
>  	buffer->input[0] = (1 | (radio<<8) | (disable << 16));
>  	dell_send_request(buffer, 17, 11);
>  
> @@ -571,6 +578,7 @@ static void dell_rfkill_update_sw_state(struct rfkill *rfkill, int radio,
>  	if (status & BIT(0)) {
>  		/* Has hw-switch, sync sw_state to BIOS */
>  		int block = rfkill_blocked(rfkill);
> +		clear_buffer();
>  		buffer->input[0] = (1 | (radio << 8) | (block << 16));
>  		dell_send_request(buffer, 17, 11);
>  	} else {
> @@ -774,6 +782,7 @@ static int __init dell_setup_rfkill(void)
>  	dell_send_request(buffer, 17, 11);
>  	status = buffer->output[1];
>  	buffer->input[0] = 0x2;
> +	clear_buffer();
>  	dell_send_request(buffer, 17, 11);

This clears the buffer after modifying input[0] and right before
dell_send_request... so you're sending a completely empty buffer? Is that
intentional here? I guess I would have expected the clear_buffer to be one line
earlier.

>  	hwswitch_state = buffer->output[1];
>  	release_buffer();
> -- 
> 1.7.9.5
> 
> 

-- 
Darren Hart
Intel Open Source Technology Center
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