linux-kernel - Re: [PATCH v2 2/2] misc: amd-sbi: Address copy_to/from

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Message-ID: <0d18ed52-86cf-44a3-913a-d514f7b8d4a7@suswa.mountain>
Date: Wed, 25 Jun 2025 14:43:35 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Akshay Gupta <akshay.gupta@....com>
Cc: linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org, arnd@...db.de,
	shyam-sundar.s-k@....com, gautham.shenoy@....com,
	mario.limonciello@....com, naveenkrishna.chatradhi@....com,
	anand.umarji@....com
Subject: Re: [PATCH v2 2/2] misc: amd-sbi: Address copy_to/from_user()
 warning reported in smatch

On Wed, Jun 25, 2025 at 11:07:07AM +0000, Akshay Gupta wrote:
> Smatch warnings are reported for below commit,
> 
> Commit bb13a84ed6b7 ("misc: amd-sbi: Add support for CPUID protocol")
> from Apr 28, 2025 (linux-next), leads to the following Smatch static
> checker warning:
> 
> drivers/misc/amd-sbi/rmi-core.c:376 apml_rmi_reg_xfer() warn: maybe return -EFAULT instead of the bytes remaining?
> drivers/misc/amd-sbi/rmi-core.c:394 apml_mailbox_xfer() warn: maybe return -EFAULT instead of the bytes remaining?
> drivers/misc/amd-sbi/rmi-core.c:411 apml_cpuid_xfer() warn: maybe return -EFAULT instead of the bytes remaining?
> drivers/misc/amd-sbi/rmi-core.c:428 apml_mcamsr_xfer() warn: maybe return -EFAULT instead of the bytes remaining?
> 
> copy_to/from_user() returns number of bytes, not copied.
> In case data not copied, return "-EFAULT".
> 
> Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> Closes: https://lore.kernel.org/all/aDVyO8ByVsceybk9@stanley.mountain/
> Reviewed-by: Naveen Krishna Chatradhi <naveenkrishna.chatradhi@....com>
> Signed-off-by: Akshay Gupta <akshay.gupta@....com>
> ---
> Changes from v1:
>  - Split patch as per Greg's suggestion
>  drivers/misc/amd-sbi/rmi-core.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/misc/amd-sbi/rmi-core.c b/drivers/misc/amd-sbi/rmi-core.c
> index 3570f3b269a9..9048517c088c 100644
> --- a/drivers/misc/amd-sbi/rmi-core.c
> +++ b/drivers/misc/amd-sbi/rmi-core.c
> @@ -372,7 +372,8 @@ static int apml_rmi_reg_xfer(struct sbrmi_data *data,
>  	mutex_unlock(&data->lock);
>  
>  	if (msg.rflag && !ret)

Unrelated to this patch, but it's always better to do if (ret) {.
Do error handling not success handling etc.

> -		return copy_to_user(arg, &msg, sizeof(struct apml_reg_xfer_msg));
> +		if (copy_to_user(arg, &msg, sizeof(struct apml_reg_xfer_msg)))
> +			return -EFAULT;
>  	return ret;
>  }
>  
> @@ -390,7 +391,9 @@ static int apml_mailbox_xfer(struct sbrmi_data *data, struct apml_mbox_msg __use
>  	if (ret && ret != -EPROTOTYPE)
>  		return ret;
>  
> -	return copy_to_user(arg, &msg, sizeof(struct apml_mbox_msg));
> +	if (copy_to_user(arg, &msg, sizeof(struct apml_mbox_msg)))
> +		return -EFAULT;
> +	return ret;

This fixes the -EPROTOTYPE as well.  In the original code, it would
return success where -EPROTOTYPE was intended.  It's probably worth
mentioning that in the commit message and maybe adding a test cases to
your test platform.

regards,
dan carpenter