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

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Date:   Fri, 27 Jan 2023 21:59:02 +0100
From:   Robert Richter <rrichter@....com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     Alison Schofield <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Dave Jiang <dave.jiang@...el.com>,
        Jonathan Cameron <jonathan.cameron@...wei.com>,
        <linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] cxl/mbox: Fix Payload Length check for Get Log command

On 27.01.23 11:48:59, Dan Williams wrote:
> 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>
> > ---
> > 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(-)
> 
> Looks good Robert. Do you think this is v6.2-rc material or can it wait
> for v6.3? It sounds like you have a real device that needs, so I am
> inclined to add it to cxl/fixes for this cycle.

6.3 is ok to me.

Thanks,

-Robert