Date:   Thu, 11 Feb 2021 08:01:48 -0800
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     linux-cxl@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-pci@...r.kernel.org, Bjorn Helgaas <helgaas@...nel.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        David Hildenbrand <david@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Jon Masters <jcm@...masters.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>,
        Ariel Sibley <Ariel.Sibley@...rochip.com>
Subject: Re: [PATCH v2 5/8] cxl/mem: Add a "RAW" send command

On 21-02-11 11:19:24, Jonathan Cameron wrote:
> On Tue, 9 Feb 2021 16:02:56 -0800
> Ben Widawsky <ben.widawsky@...el.com> wrote:
> 
> > The CXL memory device send interface will have a number of supported
> > commands. The raw command is not such a command. Raw commands allow
> > userspace to send a specified opcode to the underlying hardware and
> > bypass all driver checks on the command. This is useful for a couple of
> > usecases, mainly:
> > 1. Undocumented vendor specific hardware commands
> 
> This one I get.  There are things we'd love to standardize but often they
> need proving in a generation of hardware before the data is available to
> justify taking it to a standards body.  Stuff like performance stats.
> This stuff will all sit in the vendor defined range.  Maybe there is an
> argument for in driver hooks to allow proper support even for these
> (Ben mentioned this in the other branch of the thread).
> 
> > 2. Prototyping new hardware commands not yet supported by the driver
> 
> For 2, could just have a convenient place to enable this by one line patch.
> Some subsystems (SPI comes to mind) do this for their equivalent of raw
> commands.  The code is all there to enable it but you need to hook it
> up if you want to use it.  Avoids chance of a distro shipping it.
> 

I'm fine to drop #2 as a justification point, or maybe reword the commit message
to say, "you could also just do... but since we have it for #1 already..."

> > 
> > While this all sounds very powerful it comes with a couple of caveats:
> > 1. Bug reports using raw commands will not get the same level of
> >    attention as bug reports using supported commands (via taint).
> > 2. Supported commands will be rejected by the RAW command.
> 
> Perhaps I'm missing reading this point 2 (not sure the code actually does it!)
> 
> As stated what worries me as it means when we add support for a new
> bit of the spec we just broke the userspace ABI.
> 

It does not break ABI. The agreement is userspace must always use the QUERY
command to find out what commands are supported. If it tries to use a RAW
command that is a supported command, it will be rejected. In the case you
mention, that's an application bug. If there is a way to document that better
than what's already in the UAPI kdocs, I'm open to suggestions.

Unlike perhaps other UAPI, this one only promises to give you a way to determine
what commands you can use, not the list of what commands you can use.

> > 
> > With this comes new debugfs knob to allow full access to your toes with
> > your weapon of choice.
> 
> A few trivial things inline,
> 
> Jonathan
> 
> > 
> > Cc: Ariel Sibley <Ariel.Sibley@...rochip.com>
> > Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
> > Reviewed-by: Dan Williams <dan.j.williams@...el.com>
> > ---
> >  drivers/cxl/Kconfig          |  18 +++++
> >  drivers/cxl/mem.c            | 125 ++++++++++++++++++++++++++++++++++-
> >  include/uapi/linux/cxl_mem.h |  12 +++-
> >  3 files changed, 152 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
> > index c4ba3aa0a05d..08eaa8e52083 100644
> > --- a/drivers/cxl/Kconfig
> > +++ b/drivers/cxl/Kconfig
> > @@ -33,6 +33,24 @@ config CXL_MEM
> >  
> >  	  If unsure say 'm'.
> >  
> > +config CXL_MEM_RAW_COMMANDS
> > +	bool "RAW Command Interface for Memory Devices"
> > +	depends on CXL_MEM
> > +	help
> > +	  Enable CXL RAW command interface.
> > +
> > +	  The CXL driver ioctl interface may assign a kernel ioctl command
> > +	  number for each specification defined opcode. At any given point in
> > +	  time the number of opcodes that the specification defines and a device
> > +	  may implement may exceed the kernel's set of associated ioctl function
> > +	  numbers. The mismatch is either by omission, specification is too new,
> > +	  or by design. When prototyping new hardware, or developing / debugging
> > +	  the driver it is useful to be able to submit any possible command to
> > +	  the hardware, even commands that may crash the kernel due to their
> > +	  potential impact to memory currently in use by the kernel.
> > +
> > +	  If developing CXL hardware or the driver say Y, otherwise say N.
> > +
> >  config CXL_MEM_INSECURE_DEBUG
> >  	bool "CXL.mem debugging"
> >  	depends on CXL_MEM
> > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > index ce65630bb75e..6d766a994dce 100644
> > --- a/drivers/cxl/mem.c
> > +++ b/drivers/cxl/mem.c
> > @@ -1,6 +1,8 @@
> >  // SPDX-License-Identifier: GPL-2.0-only
> >  /* Copyright(c) 2020 Intel Corporation. All rights reserved. */
> >  #include <uapi/linux/cxl_mem.h>
> > +#include <linux/security.h>
> > +#include <linux/debugfs.h>
> >  #include <linux/module.h>
> >  #include <linux/mutex.h>
> >  #include <linux/cdev.h>
> > @@ -41,7 +43,14 @@
> >  
> >  enum opcode {
> >  	CXL_MBOX_OP_INVALID		= 0x0000,
> > +	CXL_MBOX_OP_RAW			= CXL_MBOX_OP_INVALID,
> > +	CXL_MBOX_OP_ACTIVATE_FW		= 0x0202,
> >  	CXL_MBOX_OP_IDENTIFY		= 0x4000,
> > +	CXL_MBOX_OP_SET_PARTITION_INFO	= 0x4101,
> > +	CXL_MBOX_OP_SET_LSA		= 0x4103,
> > +	CXL_MBOX_OP_SET_SHUTDOWN_STATE	= 0x4204,
> > +	CXL_MBOX_OP_SCAN_MEDIA		= 0x4304,
> > +	CXL_MBOX_OP_GET_SCAN_MEDIA	= 0x4305,
> >  	CXL_MBOX_OP_MAX			= 0x10000
> >  };
> >  
> > @@ -91,6 +100,8 @@ struct cxl_memdev {
> >  
> >  static int cxl_mem_major;
> >  static DEFINE_IDA(cxl_memdev_ida);
> > +static struct dentry *cxl_debugfs;
> > +static bool raw_allow_all;
> >  
> >  /**
> >   * struct cxl_mem_command - Driver representation of a memory device command
> > @@ -132,6 +143,49 @@ struct cxl_mem_command {
> >   */
> >  static struct cxl_mem_command mem_commands[] = {
> >  	CXL_CMD(IDENTIFY, NONE, 0, 0x43),
> > +#ifdef CONFIG_CXL_MEM_RAW_COMMANDS
> > +	CXL_CMD(RAW, NONE, ~0, ~0),
> > +#endif
> > +};
> > +
> > +/*
> > + * Commands that RAW doesn't permit. The rationale for each:
> > + *
> > + * CXL_MBOX_OP_ACTIVATE_FW: Firmware activation requires adjustment /
> > + * coordination of transaction timeout values at the root bridge level.
> > + *
> > + * CXL_MBOX_OP_SET_PARTITION_INFO: The device memory map may change live
> > + * and needs to be coordinated with HDM updates.
> > + *
> > + * CXL_MBOX_OP_SET_LSA: The label storage area may be cached by the
> > + * driver and any writes from userspace invalidates those contents.
> > + *
> > + * CXL_MBOX_OP_SET_SHUTDOWN_STATE: Set shutdown state assumes no writes
> > + * to the device after it is marked clean, userspace can not make that
> > + * assertion.
> > + *
> > + * CXL_MBOX_OP_[GET_]SCAN_MEDIA: The kernel provides a native error list that
> > + * is kept up to date with patrol notifications and error management.
> > + */
> > +static u16 disabled_raw_commands[] = {
> > +	CXL_MBOX_OP_ACTIVATE_FW,
> > +	CXL_MBOX_OP_SET_PARTITION_INFO,
> > +	CXL_MBOX_OP_SET_LSA,
> > +	CXL_MBOX_OP_SET_SHUTDOWN_STATE,
> > +	CXL_MBOX_OP_SCAN_MEDIA,
> > +	CXL_MBOX_OP_GET_SCAN_MEDIA,
> > +};
> > +
> > +/*
> > + * Command sets that RAW doesn't permit. All opcodes in this set are
> > + * disabled because they pass plain text security payloads over the
> > + * user/kernel boundary. This functionality is intended to be wrapped
> > + * behind the keys ABI which allows for encrypted payloads in the UAPI
> > + */
> > +static u8 security_command_sets[] = {
> > +	0x44, /* Sanitize */
> > +	0x45, /* Persistent Memory Data-at-rest Security */
> > +	0x46, /* Security Passthrough */
> >  };
> >  
> >  #define cxl_for_each_cmd(cmd)                                                  \
> > @@ -162,6 +216,16 @@ static int cxl_mem_wait_for_doorbell(struct cxl_mem *cxlm)
> >  	return 0;
> >  }
> >  
> > +static bool is_security_command(u16 opcode)
> > +{
> > +	int i;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(security_command_sets); i++)
> > +		if (security_command_sets[i] == (opcode >> 8))
> > +			return true;
> > +	return false;
> > +}
> > +
> >  static void cxl_mem_mbox_timeout(struct cxl_mem *cxlm,
> >  				 struct mbox_cmd *mbox_cmd)
> >  {
> > @@ -170,7 +234,8 @@ static void cxl_mem_mbox_timeout(struct cxl_mem *cxlm,
> >  	dev_dbg(dev, "Mailbox command (opcode: %#x size: %zub) timed out\n",
> >  		mbox_cmd->opcode, mbox_cmd->size_in);
> >  
> > -	if (IS_ENABLED(CONFIG_CXL_MEM_INSECURE_DEBUG)) {
> > +	if (!is_security_command(mbox_cmd->opcode) ||
> > +	    IS_ENABLED(CONFIG_CXL_MEM_INSECURE_DEBUG)) {
> >  		print_hex_dump_debug("Payload ", DUMP_PREFIX_OFFSET, 16, 1,
> >  				     mbox_cmd->payload_in, mbox_cmd->size_in,
> >  				     true);
> > @@ -434,6 +499,9 @@ static int handle_mailbox_cmd_from_user(struct cxl_memdev *cxlmd,
> >  		cxl_command_names[cmd->info.id].name, mbox_cmd.opcode,
> >  		cmd->info.size_in);
> >  
> > +	dev_WARN_ONCE(dev, cmd->info.id == CXL_MEM_COMMAND_ID_RAW,
> > +		      "raw command path used\n");
> > +
> >  	rc = cxl_mem_mbox_send_cmd(cxlm, &mbox_cmd);
> >  	cxl_mem_mbox_put(cxlm);
> >  	if (rc)
> > @@ -464,6 +532,29 @@ static int handle_mailbox_cmd_from_user(struct cxl_memdev *cxlmd,
> >  	return rc;
> >  }
> >  
> > +static bool cxl_mem_raw_command_allowed(u16 opcode)
> > +{
> > +	int i;
> > +
> > +	if (!IS_ENABLED(CONFIG_CXL_MEM_RAW_COMMANDS))
> > +		return false;
> > +
> > +	if (security_locked_down(LOCKDOWN_NONE))
> > +		return false;
> > +
> > +	if (raw_allow_all)
> > +		return true;
> > +
> > +	if (is_security_command(opcode))
> Given we are mixing generic calls like security_locked_down()
> and local cxl specific ones like this one, prefix the
> local versions.
> 
> cxl_is_security_command()
> 
> I'd also have a slight preference to do it for cxl_disabled_raw_commands
> and cxl_raw_allow_all though they are less important as more obviously
> local by not being function calls.
> 
> > +		return false;
> > +
> > +	for (i = 0; i < ARRAY_SIZE(disabled_raw_commands); i++)
> > +		if (disabled_raw_commands[i] == opcode)
> > +			return false;
> > +
> > +	return true;
> > +}
> > +
> >  /**
> >   * cxl_validate_cmd_from_user() - Check fields for CXL_MEM_SEND_COMMAND.
> >   * @cxlm: &struct cxl_mem device whose mailbox will be used.
> > @@ -500,6 +591,29 @@ static int cxl_validate_cmd_from_user(struct cxl_mem *cxlm,
> >  	if (send_cmd->in.size > cxlm->payload_size)
> >  		return -EINVAL;
> >  
> > +	/* Checks are bypassed for raw commands but along comes the taint! */
> > +	if (send_cmd->id == CXL_MEM_COMMAND_ID_RAW) {
> > +		const struct cxl_mem_command temp = {
> > +			.info = {
> > +				.id = CXL_MEM_COMMAND_ID_RAW,
> > +				.flags = CXL_MEM_COMMAND_FLAG_NONE,
> > +				.size_in = send_cmd->in.size,
> > +				.size_out = send_cmd->out.size,
> > +			},
> > +			.opcode = send_cmd->raw.opcode
> > +		};
> > +
> > +		if (send_cmd->raw.rsvd)
> > +			return -EINVAL;
> > +
> > +		if (!cxl_mem_raw_command_allowed(send_cmd->raw.opcode))
> > +			return -EPERM;
> > +
> > +		memcpy(out_cmd, &temp, sizeof(temp));
> > +
> > +		return 0;
> > +	}
> > +
> >  	if (send_cmd->flags & ~CXL_MEM_COMMAND_FLAG_MASK)
> >  		return -EINVAL;
> >  
> > @@ -1123,8 +1237,9 @@ static struct pci_driver cxl_mem_driver = {
> >  
> >  static __init int cxl_mem_init(void)
> >  {
> > -	int rc;
> > +	struct dentry *mbox_debugfs;
> >  	dev_t devt;
> > +	int rc;
> 
> Shuffle this back to the place it was introduced to reduce patch noise.
> 
> >  
> >  	rc = alloc_chrdev_region(&devt, 0, CXL_MEM_MAX_DEVS, "cxl");
> >  	if (rc)
> > @@ -1139,11 +1254,17 @@ static __init int cxl_mem_init(void)
> >  		return rc;
> >  	}
> >  
> > +	cxl_debugfs = debugfs_create_dir("cxl", NULL);
> > +	mbox_debugfs = debugfs_create_dir("mbox", cxl_debugfs);
> > +	debugfs_create_bool("raw_allow_all", 0600, mbox_debugfs,
> > +			    &raw_allow_all);
> > +
> >  	return 0;
> >  }
> >  
> >  static __exit void cxl_mem_exit(void)
> >  {
> > +	debugfs_remove_recursive(cxl_debugfs);
> >  	pci_unregister_driver(&cxl_mem_driver);
> >  	unregister_chrdev_region(MKDEV(cxl_mem_major, 0), CXL_MEM_MAX_DEVS);
> >  }
> > diff --git a/include/uapi/linux/cxl_mem.h b/include/uapi/linux/cxl_mem.h
> > index f1f7e9f32ea5..72d1eb601a5d 100644
> > --- a/include/uapi/linux/cxl_mem.h
> > +++ b/include/uapi/linux/cxl_mem.h
> > @@ -22,6 +22,7 @@
> >  #define CXL_CMDS                                                          \
> >  	___C(INVALID, "Invalid Command"),                                 \
> >  	___C(IDENTIFY, "Identify Command"),                               \
> > +	___C(RAW, "Raw device command"),                                  \
> >  	___C(MAX, "Last command")
> >  
> >  #define ___C(a, b) CXL_MEM_COMMAND_ID_##a
> > @@ -112,6 +113,9 @@ struct cxl_mem_query_commands {
> >   * @id: The command to send to the memory device. This must be one of the
> >   *	commands returned by the query command.
> >   * @flags: Flags for the command (input).
> > + * @raw: Special fields for raw commands
> > + * @raw.opcode: Opcode passed to hardware when using the RAW command.
> > + * @raw.rsvd: Must be zero.
> >   * @rsvd: Must be zero.
> >   * @retval: Return value from the memory device (output).
> >   * @in.size: Size of the payload to provide to the device (input).
> > @@ -133,7 +137,13 @@ struct cxl_mem_query_commands {
> >  struct cxl_send_command {
> >  	__u32 id;
> >  	__u32 flags;
> > -	__u32 rsvd;
> > +	union {
> > +		struct {
> > +			__u16 opcode;
> > +			__u16 rsvd;
> > +		} raw;
> > +		__u32 rsvd;
> > +	};
> >  	__u32 retval;
> >  
> >  	struct {
> 

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