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Date:   Mon, 1 Feb 2021 13:28:48 -0500
From:   Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To:     Ben Widawsky <ben.widawsky@intel.com>
Cc:     linux-cxl@vger.kernel.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org,
        linux-pci@vger.kernel.org, Bjorn Helgaas <helgaas@kernel.org>,
        Chris Browy <cbrowy@avery-design.com>,
        Christoph Hellwig <hch@infradead.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Jon Masters <jcm@jonmasters.org>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Rafael Wysocki <rafael.j.wysocki@intel.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Vishal Verma <vishal.l.verma@intel.com>,
        daniel.lll@alibaba-inc.com,
        "John Groves (jgroves)" <jgroves@micron.com>,
        "Kelley, Sean V" <sean.v.kelley@intel.com>
Subject: Re: [PATCH 13/14] cxl/mem: Add limited Get Log command (0401h)
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References: <20210130002438.1872527-1-ben.widawsky@intel.com>
 <20210130002438.1872527-14-ben.widawsky@intel.com>
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On Fri, Jan 29, 2021 at 04:24:37PM -0800, Ben Widawsky wrote:
> The Get Log command returns the actual log entries that are advertised
> via the Get Supported Logs command (0400h). CXL device logs are selected
> by UUID which is part of the CXL spec. Because the driver tries to
> sanitize what is sent to hardware, there becomes a need to restrict the
> types of logs which can be accessed by userspace. For example, the
> vendor specific log might only be consumable by proprietary, or offline
> applications, and therefore a good candidate for userspace.
> 
> The current driver infrastructure does allow basic validation for all
> commands, but doesn't inspect any of the payload data. Along with Get
> Log support comes new infrastructure to add a hook for payload
> validation. This infrastructure is used to filter out the CEL UUID,
> which the userspace driver doesn't have business knowing, and taints on
> invalid UUIDs being sent to hardware.

Perhaps a better option is to reject invalid UUIDs?

And if you really really want to use invalid UUIDs then:

1) Make that code wrapped in CONFIG_CXL_DEBUG_THIS_IS_GOING_TO..?

2) Wrap it with lockdown code so that you can't do this at all
   when in LOCKDOWN_INTEGRITY or such?

> 
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> ---
>  drivers/cxl/mem.c            | 42 +++++++++++++++++++++++++++++++++++-
>  include/uapi/linux/cxl_mem.h |  1 +
>  2 files changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> index b8ca6dff37b5..086268f1dd6c 100644
> --- a/drivers/cxl/mem.c
> +++ b/drivers/cxl/mem.c
> @@ -119,6 +119,8 @@ static const uuid_t log_uuid[] = {
>  				 0x07, 0x19, 0x40, 0x3d, 0x86)
>  };
>  
> +static int validate_log_uuid(void __user *payload, size_t size);
> +
>  /**
>   * struct cxl_mem_command - Driver representation of a memory device command
>   * @info: Command information as it exists for the UAPI
> @@ -132,6 +134,10 @@ static const uuid_t log_uuid[] = {
>   *  * %CXL_CMD_INTERNAL_FLAG_PSEUDO: This is a pseudo command which doesn't have
>   *    a direct mapping to hardware. They are implicitly always enabled.
>   *
> + * @validate_payload: A function called after the command is validated but
> + * before it's sent to the hardware. The primary purpose is to validate, or
> + * fixup the actual payload.
> + *
>   * The cxl_mem_command is the driver's internal representation of commands that
>   * are supported by the driver. Some of these commands may not be supported by
>   * the hardware. The driver will use @info to validate the fields passed in by
> @@ -147,9 +153,11 @@ struct cxl_mem_command {
>  #define CXL_CMD_INTERNAL_FLAG_HIDDEN BIT(0)
>  #define CXL_CMD_INTERNAL_FLAG_MANDATORY BIT(1)
>  #define CXL_CMD_INTERNAL_FLAG_PSEUDO BIT(2)
> +
> +	int (*validate_payload)(void __user *payload, size_t size);
>  };
>  
> -#define CXL_CMD(_id, _flags, sin, sout, f)                                     \
> +#define CXL_CMD_VALIDATE(_id, _flags, sin, sout, f, v)                         \
>  	[CXL_MEM_COMMAND_ID_##_id] = {                                         \
>  	.info =	{                                                              \
>  			.id = CXL_MEM_COMMAND_ID_##_id,                        \
> @@ -159,8 +167,12 @@ struct cxl_mem_command {
>  		},                                                             \
>  	.flags = CXL_CMD_INTERNAL_FLAG_##f,                                    \
>  	.opcode = CXL_MBOX_OP_##_id,                                           \
> +	.validate_payload = v,                                                 \
>  	}
>  
> +#define CXL_CMD(_id, _flags, sin, sout, f)                                     \
> +	CXL_CMD_VALIDATE(_id, _flags, sin, sout, f, NULL)
> +
>  /*
>   * This table defines the supported mailbox commands for the driver. This table
>   * is made up of a UAPI structure. Non-negative values as parameters in the
> @@ -176,6 +188,8 @@ static struct cxl_mem_command mem_commands[] = {
>  	CXL_CMD(GET_PARTITION_INFO, NONE, 0, 0x20, NONE),
>  	CXL_CMD(GET_LSA, NONE, 0x8, ~0, MANDATORY),
>  	CXL_CMD(GET_HEALTH_INFO, NONE, 0, 0x12, MANDATORY),
> +	CXL_CMD_VALIDATE(GET_LOG, MUTEX, 0x18, ~0, MANDATORY,
> +			 validate_log_uuid),
>  };
>  
>  /*
> @@ -563,6 +577,13 @@ static int handle_mailbox_cmd_from_user(struct cxl_memdev *cxlmd,
>  			kvzalloc(cxlm->mbox.payload_size, GFP_KERNEL);
>  
>  	if (cmd->info.size_in) {
> +		if (cmd->validate_payload) {
> +			rc = cmd->validate_payload(u64_to_user_ptr(in_payload),
> +						   cmd->info.size_in);
> +			if (rc)
> +				goto out;
> +		}
> +
>  		mbox_cmd.payload_in = kvzalloc(cmd->info.size_in, GFP_KERNEL);
>  		if (!mbox_cmd.payload_in) {
>  			rc = -ENOMEM;
> @@ -1205,6 +1226,25 @@ struct cxl_mbox_get_log {
>  	__le32 length;
>  } __packed;
>  
> +static int validate_log_uuid(void __user *input, size_t size)
> +{
> +	struct cxl_mbox_get_log __user *get_log = input;
> +	uuid_t payload_uuid;
> +
> +	if (copy_from_user(&payload_uuid, &get_log->uuid, sizeof(uuid_t)))
> +		return -EFAULT;
> +
> +	/* All unspec'd logs shall taint */
> +	if (uuid_equal(&payload_uuid, &log_uuid[CEL_UUID]))
> +		return 0;
> +	if (uuid_equal(&payload_uuid, &log_uuid[DEBUG_UUID]))
> +		return 0;
> +
> +	add_taint(TAINT_RAW_PASSTHROUGH, LOCKDEP_STILL_OK);
> +
> +	return 0;
> +}
> +
>  static int cxl_xfer_log(struct cxl_mem *cxlm, uuid_t *uuid, u32 size, u8 *out)
>  {
>  	u32 remaining = size;
> diff --git a/include/uapi/linux/cxl_mem.h b/include/uapi/linux/cxl_mem.h
> index 766c231d6150..7cdc7f7ce7ec 100644
> --- a/include/uapi/linux/cxl_mem.h
> +++ b/include/uapi/linux/cxl_mem.h
> @@ -39,6 +39,7 @@ extern "C" {
>  	___C(GET_PARTITION_INFO, "Get Partition Information"),            \
>  	___C(GET_LSA, "Get Label Storage Area"),                          \
>  	___C(GET_HEALTH_INFO, "Get Health Info"),                         \
> +	___C(GET_LOG, "Get Log"),                                         \
>  	___C(MAX, "Last command")
>  
>  #define ___C(a, b) CXL_MEM_COMMAND_ID_##a
> -- 
> 2.30.0
>