linux-kernel - Re: [PATCH v3] cxl/mbox: Fix Payload Length check for Get Log command

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Message-ID: <Y8kHps1w9SVM/kg+@rric.localdomain>
Date:   Thu, 19 Jan 2023 10:04:38 +0100
From:   Robert Richter <rrichter@....com>
To:     Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>
CC:     Jonathan Cameron <jonathan.cameron@...wei.com>,
        <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] cxl/mbox: Fix Payload Length check for Get Log command

On 19.01.23 09:20:53, Robert Richter 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@....com>
> ---
> 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)

Please ignore that version, I accidentally sent it out untested. Sorry
for that. I will send a v4 instead.

-Robert