Re: [PATCH v4] cxl/mbox: Fix Payload Length check for Get Log command

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 19 Jan 2023 10:49:34 +0100
Robert Richter <rrichter@amd.com> wrote:

> Commit 2aeaf663b85e introduced strict checking for variable length
> payload size validation. The payload length of received data must
> match the size of the requested data by the caller except for the case
> where the min_out value is set.
> 
> The Get Log command does not have a header with a length field set.
> The Log size is determined by the Get Supported Logs command (CXL 3.0,
> 8.2.9.5.1). However, the actual size can be smaller and the number of
> valid bytes in the payload output must be determined reading the
> Payload Length field (CXL 3.0, Table 8-36, Note 2).
> 
> Two issues arise: The command can successfully complete with a payload
> length of zero. And, the valid payload length must then also be
> consumed by the caller.
> 
> Change cxl_xfer_log() to pass the number of payload bytes back to the
> caller to determine the number of log entries. Implement the payload
> handling as a special case where mbox_cmd->size_out is consulted when
> cxl_internal_send_cmd() returns -EIO. A WARN_ONCE() is added to check
> that -EIO is only returned in case of an unexpected output size.
> 
> Logs can be bigger than the maximum payload length and multiple Get
> Log commands can be issued. If the received payload size is smaller
> than the maximum payload size we can assume all valid bytes have been
> fetched. Stop sending further Get Log commands then.
> 
> On that occasion, change debug messages to also report the opcodes of
> supported commands.
> 
> The variable payload commands GET_LSA and SET_LSA are not affected by
> this strict check: SET_LSA cannot be broken because SET_LSA does not
> return an output payload, and GET_LSA never expects short reads.
> 
> Fixes: 2aeaf663b85e ("cxl/mbox: Add variable output size validation for internal commands")
> Signed-off-by: Robert Richter <rrichter@amd.com>
LGTM

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
> v4:
>  * Fixed a build issue.
> v3:
>  * Added comment to the WARN_ONCE(). (Jonathan)
>  * Passing a size pointer to report the payload size back. (Jonathan)
>  * Moved logging of supported opcodes out of this patch for a separate
>    change. (Jonathan)
> 
>  drivers/cxl/core/mbox.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index b03fba212799..a48ade466d6a 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -170,6 +170,12 @@ int cxl_internal_send_cmd(struct cxl_dev_state *cxlds,
>  	out_size = mbox_cmd->size_out;
>  	min_out = mbox_cmd->min_out;
>  	rc = cxlds->mbox_send(cxlds, mbox_cmd);
> +	/*
> +	 * EIO is reserved for a payload size mismatch and mbox_send()
> +	 * may not return this error.
> +	 */
> +	if (WARN_ONCE(rc == -EIO, "Bad return code: -EIO"))
> +		return -ENXIO;
>  	if (rc)
>  		return rc;
>  
> @@ -550,9 +556,9 @@ int cxl_send_cmd(struct cxl_memdev *cxlmd, struct cxl_send_command __user *s)
>  	return 0;
>  }
>  
> -static int cxl_xfer_log(struct cxl_dev_state *cxlds, uuid_t *uuid, u32 size, u8 *out)
> +static int cxl_xfer_log(struct cxl_dev_state *cxlds, uuid_t *uuid, u32 *size, u8 *out)
>  {
> -	u32 remaining = size;
> +	u32 remaining = *size;
>  	u32 offset = 0;
>  
>  	while (remaining) {
> @@ -576,6 +582,17 @@ static int cxl_xfer_log(struct cxl_dev_state *cxlds, uuid_t *uuid, u32 size, u8
>  		};
>  
>  		rc = cxl_internal_send_cmd(cxlds, &mbox_cmd);
> +
> +		/*
> +		 * The output payload length that indicates the number
> +		 * of valid bytes can be smaller than the Log buffer
> +		 * size.
> +		 */
> +		if (rc == -EIO && mbox_cmd.size_out < xfer_size) {
> +			offset += mbox_cmd.size_out;
> +			break;
> +		}
> +
>  		if (rc < 0)
>  			return rc;
>  
> @@ -584,6 +601,8 @@ static int cxl_xfer_log(struct cxl_dev_state *cxlds, uuid_t *uuid, u32 size, u8
>  		offset += xfer_size;
>  	}
>  
> +	*size = offset;
> +
>  	return 0;
>  }
>  
> @@ -694,7 +713,7 @@ int cxl_enumerate_cmds(struct cxl_dev_state *cxlds)
>  			goto out;
>  		}
>  
> -		rc = cxl_xfer_log(cxlds, &uuid, size, log);
> +		rc = cxl_xfer_log(cxlds, &uuid, &size, log);
>  		if (rc) {
>  			kvfree(log);
>  			goto out;
> 
> base-commit: 1b929c02afd37871d5afb9d498426f83432e71c2