Re: [PATCH v4 4/9] cxl/mem: Add basic IOCTL interface

Ben Widawsky
2021-02-16T17:54:26Z

On 21-02-16 15:22:23, Jonathan Cameron wrote:
> On Mon, 15 Feb 2021 17:45:33 -0800
> Ben Widawsky <ben.widawsky@intel.com> wrote:
>
> > Add a straightforward IOCTL that provides a mechanism for userspace to
> > query the supported memory device commands. CXL commands as they appear
> > to userspace are described as part of the UAPI kerneldoc. The command
> > list returned via this IOCTL will contain the full set of commands that
> > the driver supports, however, some of those commands may not be
> > available for use by userspace.
> >
> > Memory device commands first appear in the CXL 2.0 specification. They
> > are submitted through a mailbox mechanism specified in the CXL 2.0
> > specification.
> >
> > The send command allows userspace to issue mailbox commands directly to
> > the hardware. The list of available commands to send are the output of
> > the query command. The driver verifies basic properties of the command
> > and possibly inspect the input (or output) payload to determine whether
> > or not the command is allowed (or might taint the kernel).
> >
> > Reported-by: kernel test robot <lkp@intel.com> # bug in earlier revision
> > Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
> > Reviewed-by: Dan Williams <dan.j.williams@intel.com> (v2)
>
> I may be missreading this but I think the logic to ensure commands
> using a variable sized buffer have enough space is broken.
>
> Jonathan
>
> > ---
> > .clang-format | 1 +
> > .../userspace-api/ioctl/ioctl-number.rst | 1 +
> > drivers/cxl/mem.c | 288 +++++++++++++++++-
> > include/uapi/linux/cxl_mem.h | 154 ++++++++++
> > 4 files changed, 443 insertions(+), 1 deletion(-)
> > create mode 100644 include/uapi/linux/cxl_mem.h
> >
> > diff --git a/.clang-format b/.clang-format
> > index 10dc5a9a61b3..3f11c8901b43 100644
> > --- a/.clang-format
> > +++ b/.clang-format
> > @@ -109,6 +109,7 @@ ForEachMacros:
> > - 'css_for_each_child'
> > - 'css_for_each_descendant_post'
> > - 'css_for_each_descendant_pre'
> > + - 'cxl_for_each_cmd'
> > - 'device_for_each_child_node'
> > - 'dma_fence_chain_for_each'
> > - 'do_for_each_ftrace_op'
> > diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
> > index a4c75a28c839..6eb8e634664d 100644
> > --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
> > +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
> > @@ -352,6 +352,7 @@ Code Seq# Include File Comments
> > <mailto:michael.klein@puffin.lb.shuttle.de>
> > 0xCC 00-0F drivers/misc/ibmvmc.h pseries VMC driver
> > 0xCD 01 linux/reiserfs_fs.h
> > +0xCE 01-02 uapi/linux/cxl_mem.h Compute Express Link Memory Devices
> > 0xCF 02 fs/cifs/ioctl.c
> > 0xDB 00-0F drivers/char/mwave/mwavepub.h
> > 0xDD 00-3F ZFCP device driver see drivers/s390/scsi/
> > diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
> > index 410adb1bdffc..a4298cb1182d 100644
> > --- a/drivers/cxl/mem.c
> > +++ b/drivers/cxl/mem.c
> > @@ -1,5 +1,6 @@
> > // SPDX-License-Identifier: GPL-2.0-only
> > /* Copyright(c) 2020 Intel Corporation. All rights reserved. */
> > +#include <uapi/linux/cxl_mem.h>
> > #include <linux/module.h>
> > #include <linux/mutex.h>
> > #include <linux/cdev.h>
> > @@ -40,6 +41,7 @@
> > #define CXL_MAILBOX_TIMEOUT_MS (2 * HZ)
> >
> > enum opcode {
> > + CXL_MBOX_OP_INVALID = 0x0000,
> > CXL_MBOX_OP_IDENTIFY = 0x4000,
> > CXL_MBOX_OP_MAX = 0x10000
> > };
> > @@ -91,6 +93,49 @@ struct cxl_memdev {
> > static int cxl_mem_major;
> > static DEFINE_IDA(cxl_memdev_ida);
> >
> > +/**
> > + * struct cxl_mem_command - Driver representation of a memory device command
> > + * @info: Command information as it exists for the UAPI
> > + * @opcode: The actual bits used for the mailbox protocol
> > + *
> > + * 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
> > + * the user then submit the @opcode to the hardware.
> > + *
> > + * See struct cxl_command_info.
> > + */
> > +struct cxl_mem_command {
> > + struct cxl_command_info info;
> > + enum opcode opcode;
> > +};
> > +
> > +#define CXL_CMD(_id, sin, sout) \
> > + [CXL_MEM_COMMAND_ID_##_id] = { \
> > + .info = { \
> > + .id = CXL_MEM_COMMAND_ID_##_id, \
> > + .size_in = sin, \
> > + .size_out = sout, \
> > + }, \
> > + .opcode = CXL_MBOX_OP_##_id, \
> > + }
> > +
> > +/*
> > + * 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
> > + * table will be validated against the user's input. For example, if size_in is
> > + * 0, and the user passed in 1, it is an error.
> > + */
> > +static struct cxl_mem_command mem_commands[] = {
> > + CXL_CMD(IDENTIFY, 0, 0x43),
> > +};
> > +
> > +#define cxl_for_each_cmd(cmd) \
> > + for ((cmd) = &mem_commands[0]; \
> > + ((cmd) - mem_commands) < ARRAY_SIZE(mem_commands); (cmd)++)
> > +
> > +#define cxl_cmd_count ARRAY_SIZE(mem_commands)
> > +
> > static int cxl_mem_wait_for_doorbell(struct cxl_mem *cxlm)
> > {
> > const unsigned long start = jiffies;
> > @@ -312,6 +357,247 @@ static void cxl_mem_mbox_put(struct cxl_mem *cxlm)
> > mutex_unlock(&cxlm->mbox_mutex);
> > }
> >
> > +/**
> > + * handle_mailbox_cmd_from_user() - Dispatch a mailbox command for userspace.
> > + * @cxlm: The CXL memory device to communicate with.
> > + * @cmd: The validated command.
> > + * @in_payload: Pointer to userspace's input payload.
> > + * @out_payload: Pointer to userspace's output payload.
> > + * @size_out: (Input) Max payload size to copy out.
> > + * (Output) Payload size hardware generated.
> > + * @retval: Hardware generated return code from the operation.
> > + *
> > + * Return:
> > + * * %0 - Mailbox transaction succeeded. This implies the mailbox
> > + * protocol completed successfully not that the operation itself
> > + * was successful.
> > + * * %-ENOMEM - Couldn't allocate a bounce buffer.
> > + * * %-EFAULT - Something happened with copy_to/from_user.
> > + * * %-EINTR - Mailbox acquisition interrupted.
> > + * * %-* - Transaction level failures.
> > + *
> > + * Creates the appropriate mailbox command and dispatches it on behalf of a
> > + * userspace request. The input and output payloads are copied between
> > + * userspace.
> > + *
> > + * See cxl_send_cmd().
> > + */
> > +static int handle_mailbox_cmd_from_user(struct cxl_mem *cxlm,
> > + const struct cxl_mem_command *cmd,
> > + u64 in_payload, u64 out_payload,
> > + s32 *size_out, u32 *retval)
> > +{
> > + struct device *dev = &cxlm->pdev->dev;
> > + struct mbox_cmd mbox_cmd = {
> > + .opcode = cmd->opcode,
> > + .size_in = cmd->info.size_in,
> > + };
> > + int rc;
> > +
> > + if (cmd->info.size_out) {
> > + mbox_cmd.payload_out = kvzalloc(cmd->info.size_out, GFP_KERNEL);
> > + if (!mbox_cmd.payload_out)
> > + return -ENOMEM;
> > + }
> > +
> > + if (cmd->info.size_in) {
> > + mbox_cmd.payload_in = kvzalloc(cmd->info.size_in, GFP_KERNEL);
> > + if (!mbox_cmd.payload_in) {
> > + rc = -ENOMEM;
> > + goto out;
> > + }
> > +
> > + if (copy_from_user(mbox_cmd.payload_in,
> > + u64_to_user_ptr(in_payload),
> > + cmd->info.size_in)) {
> > + rc = -EFAULT;
> > + goto out;
> > + }
> > + }
> > +
> > + rc = cxl_mem_mbox_get(cxlm);
> > + if (rc)
> > + goto out;
> > +
> > + dev_dbg(dev,
> > + "Submitting %s command for user\n"
> > + "\topcode: %x\n"
> > + "\tsize: %ub\n",
> > + cxl_command_names[cmd->info.id].name, mbox_cmd.opcode,
> > + cmd->info.size_in);
> > +
> > + rc = __cxl_mem_mbox_send_cmd(cxlm, &mbox_cmd);
> > + cxl_mem_mbox_put(cxlm);
> > + if (rc)
> > + goto out;
> > +
> > + /*
> > + * @size_out contains the max size that's allowed to be written back out
> > + * to userspace. While the payload may have written more output than
> > + * this it will have to be ignored.
> > + */
>
> See below for why I don't think this works. The size of mbox_cmd.payload_out
> seems to always be the size userspace specified, never the 1MB this code
> is assuming. So if the hardware returns more than userspace asks for you
> have a buffer overrun.
>
>
> > + if (mbox_cmd.size_out) {
> > + if (copy_to_user(u64_to_user_ptr(out_payload),
> > + mbox_cmd.payload_out, *size_out)) {
> > + rc = -EFAULT;
> > + goto out;
> > + }
> > + }
> > +
> > + /*
> > + * Reporting the actual size, even if it was greater than @size_out
> > + * allows userspace to try the command again with a bigger buffer.
> > + */
> > + *size_out = mbox_cmd.size_out;
> > + *retval = mbox_cmd.return_code;
> > +
> > +out:
> > + kvfree(mbox_cmd.payload_in);
> > + kvfree(mbox_cmd.payload_out);
> > + return rc;
> > +}
> > +
> > +/**
> > + * cxl_validate_cmd_from_user() - Check fields for CXL_MEM_SEND_COMMAND.
> > + * @cxlm: &struct cxl_mem device whose mailbox will be used.
> > + * @send_cmd: &struct cxl_send_command copied in from userspace.
> > + * @out_cmd: Sanitized and populated &struct cxl_mem_command.
> > + *
> > + * Return:
> > + * * %0 - @out_cmd is ready to send.
> > + * * %-ENOTTY - Invalid command specified.
> > + * * %-EINVAL - Reserved fields or invalid values were used.
> > + * * %-ENOMEM - Input or output buffer wasn't sized properly.
> > + *
> > + * The result of this command is a fully validated command in @out_cmd that is
> > + * safe to send to the hardware.
> > + *
> > + * See handle_mailbox_cmd_from_user()
> > + */
> > +static int cxl_validate_cmd_from_user(struct cxl_mem *cxlm,
> > + const struct cxl_send_command *send_cmd,
> > + struct cxl_mem_command *out_cmd)
> > +{
> > + const struct cxl_command_info *info;
> > + struct cxl_mem_command *c;
> > +
> > + if (send_cmd->id == 0 || send_cmd->id >= CXL_MEM_COMMAND_ID_MAX)
> > + return -ENOTTY;
> > +
> > + /*
> > + * The user can never specify an input payload larger than what hardware
> > + * supports, but output can be arbitrarily large (simply write out as
> > + * much data as the hardware provides).
> > + */
> > + if (send_cmd->in.size > cxlm->payload_size)
> > + return -EINVAL;
> > +
> > + if (send_cmd->flags & ~CXL_MEM_COMMAND_FLAG_MASK)
> > + return -EINVAL;
> > +
> > + if (send_cmd->rsvd)
> > + return -EINVAL;
> > +
> > + if (send_cmd->in.rsvd || send_cmd->out.rsvd)
> > + return -EINVAL;
> > +
> > + /* Convert user's command into the internal representation */
> > + c = &mem_commands[send_cmd->id];
> > + info = &c->info;
> > +
> > + /* Check the input buffer is the expected size */
> > + if (info->size_in >= 0 && info->size_in != send_cmd->in.size)
> > + return -ENOMEM;
> > +
> > + /* Check the output buffer is at least large enough */
> > + if (info->size_out >= 0 && send_cmd->out.size < info->size_out)
> > + return -ENOMEM;
> > +
> > + memcpy(out_cmd, c, sizeof(*c));
> > + out_cmd->info.size_in = send_cmd->in.size;
> > + out_cmd->info.size_out = send_cmd->out.size;
> > +
> > + return 0;
> > +}
> > +
> > +static int cxl_query_cmd(struct cxl_memdev *cxlmd,
> > + struct cxl_mem_query_commands __user *q)
> > +{
> > + struct device *dev = &cxlmd->dev;
> > + struct cxl_mem_command *cmd;
> > + u32 n_commands;
> > + int j = 0;
> > +
> > + dev_dbg(dev, "Query IOCTL\n");
> > +
> > + if (get_user(n_commands, &q->n_commands))
> > + return -EFAULT;
> > +
> > + /* returns the total number if 0 elements are requested. */
> > + if (n_commands == 0)
> > + return put_user(cxl_cmd_count, &q->n_commands);
> > +
> > + /*
> > + * otherwise, return max(n_commands, total commands) cxl_command_info
> > + * structures.
> > + */
> > + cxl_for_each_cmd(cmd) {
> > + const struct cxl_command_info *info = &cmd->info;
> > +
> > + if (copy_to_user(&q->commands[j++], info, sizeof(*info)))
> > + return -EFAULT;
> > +
> > + if (j == n_commands)
> > + break;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static int cxl_send_cmd(struct cxl_memdev *cxlmd,
> > + struct cxl_send_command __user *s)
> > +{
> > + struct cxl_mem *cxlm = cxlmd->cxlm;
> > + struct device *dev = &cxlmd->dev;
> > + struct cxl_send_command send;
> > + struct cxl_mem_command c;
> > + int rc;
> > +
> > + dev_dbg(dev, "Send IOCTL\n");
> > +
> > + if (copy_from_user(&send, s, sizeof(send)))
> > + return -EFAULT;
> > +
> > + rc = cxl_validate_cmd_from_user(cxlmd->cxlm, &send, &c);
> > + if (rc)
> > + return rc;
>
> Userspace will pass in send.out set to the size of it's available buffer.
> Then cxl_validate_cmd_from_user() will fill
> c.info.size_out with send.out.size
>
> > +
> > + /* Prepare to handle a full payload for variable sized output */
> > + if (c.info.size_out < 0)
>
> So this check only works if userspace set the command to have variable size.
> That's not what the docs below suggest should happen.
>

Another good catch. This bug was introduced after the last change was made. I
still don't want to have a size_out as part of the mailbox command.

Validate should not alter the size_out field except in the case of RAW commands.

I believe this is the right fix, handle_mailbox_cmd_from_user() already will
only copy_to the right number of byte, but your eyes on it are appreciated.

diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index 237b956f0be0..4ca4f5afd9d2 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -686,7 +686,11 @@ static int cxl_validate_cmd_from_user(struct cxl_mem *cxlm,

memcpy(out_cmd, c, sizeof(*c));
out_cmd->info.size_in = send_cmd->in.size;
- out_cmd->info.size_out = send_cmd->out.size;
+ /*
+ * XXX: out_cmd->info.size_out will be controlled by the driver, and the
+ * specified number of bytes @send_cmd->out.size will be copied back out
+ * to userspace.
+ */

return 0;
}

> > + c.info.size_out = cxlm->payload_size;
> > +
> > + rc = handle_mailbox_cmd_from_user(cxlm, &c, send.in.payload,
> > + send.out.payload, &send.out.size,
> > + &send.retval);
> > + if (rc)
> > + return rc;
> > +
> > + return copy_to_user(s, &send, sizeof(send));
> > +}
> > +
> > +static long __cxl_memdev_ioctl(struct cxl_memdev *cxlmd, unsigned int cmd,
> > + unsigned long arg)
> > +{
> > + switch (cmd) {
> > + case CXL_MEM_QUERY_COMMANDS:
> > + return cxl_query_cmd(cxlmd, (void __user *)arg);
> > + case CXL_MEM_SEND_COMMAND:
> > + return cxl_send_cmd(cxlmd, (void __user *)arg);
> > + default:
> > + return -ENOTTY;
> > + }
> > +}
> > +
> > static long cxl_memdev_ioctl(struct file *file, unsigned int cmd,
> > unsigned long arg)
> > {
> > @@ -325,7 +611,7 @@ static long cxl_memdev_ioctl(struct file *file, unsigned int cmd,
> > if (!percpu_ref_tryget_live(&cxlmd->ops_active))
> > return -ENXIO;
> >
> > - /* TODO: ioctl body */
> > + rc = __cxl_memdev_ioctl(cxlmd, cmd, arg);
> >
> > percpu_ref_put(&cxlmd->ops_active);
> >
> > diff --git a/include/uapi/linux/cxl_mem.h b/include/uapi/linux/cxl_mem.h
> > new file mode 100644
> > index 000000000000..18cea908ad0b
> > --- /dev/null
> > +++ b/include/uapi/linux/cxl_mem.h
> > @@ -0,0 +1,154 @@
> > +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> > +/*
> > + * CXL IOCTLs for Memory Devices
> > + */
> > +
> > +#ifndef _UAPI_CXL_MEM_H_
> > +#define _UAPI_CXL_MEM_H_
> > +
> > +#include <linux/types.h>
> > +
> > +/**
> > + * DOC: UAPI
> > + *
> > + * Not all of all commands that the driver supports are always available for use
> > + * by userspace. Userspace must check the results from the QUERY command in
> > + * order to determine the live set of commands.
> > + */
> > +
> > +#define CXL_MEM_QUERY_COMMANDS _IOR(0xCE, 1, struct cxl_mem_query_commands)
> > +#define CXL_MEM_SEND_COMMAND _IOWR(0xCE, 2, struct cxl_send_command)
> > +
> > +#define CXL_CMDS \
> > + ___C(INVALID, "Invalid Command"), \
> > + ___C(IDENTIFY, "Identify Command"), \
> > + ___C(MAX, "invalid / last command")
> > +
> > +#define ___C(a, b) CXL_MEM_COMMAND_ID_##a
> > +enum { CXL_CMDS };
> > +
> > +#undef ___C
> > +#define ___C(a, b) { b }
> > +static const struct {
> > + const char *name;
> > +} cxl_command_names[] = { CXL_CMDS };
> > +
> > +/*
> > + * Here's how this actually breaks out:
> > + * cxl_command_names[] = {
> > + * [CXL_MEM_COMMAND_ID_INVALID] = { "Invalid Command" },
> > + * [CXL_MEM_COMMAND_ID_IDENTIFY] = { "Identify Command" },
> > + * ...
> > + * [CXL_MEM_COMMAND_ID_MAX] = { "invalid / last command" },
> > + * };
> > + */
>
> Thanks, this is great.
>
> > +
> > +#undef ___C
> > +
> > +/**
> > + * struct cxl_command_info - Command information returned from a query.
> > + * @id: ID number for the command.
> > + * @flags: Flags that specify command behavior.
> > + * @size_in: Expected input size, or -1 if variable length.
> > + * @size_out: Expected output size, or -1 if variable length.
> > + *
> > + * Represents a single command that is supported by both the driver and the
> > + * hardware. This is returned as part of an array from the query ioctl. The
> > + * following would be a command that takes a variable length input and returns 0
> > + * bytes of output.
> > + *
> > + * - @id = 10
> > + * - @flags = 0
> > + * - @size_in = -1
> > + * - @size_out = 0
> > + *
> > + * See struct cxl_mem_query_commands.
> > + */
> > +struct cxl_command_info {
> > + __u32 id;
> > +
> > + __u32 flags;
> > +#define CXL_MEM_COMMAND_FLAG_MASK GENMASK(0, 0)
> > +
> > + __s32 size_in;
> > + __s32 size_out;
> > +};
> > +
> > +/**
> > + * struct cxl_mem_query_commands - Query supported commands.
> > + * @n_commands: In/out parameter. When @n_commands is > 0, the driver will
> > + * return min(num_support_commands, n_commands). When @n_commands
> > + * is 0, driver will return the number of total supported commands.
> > + * @rsvd: Reserved for future use.
> > + * @commands: Output array of supported commands. This array must be allocated
> > + * by userspace to be at least min(num_support_commands, @n_commands)
> > + *
> > + * Allow userspace to query the available commands supported by both the driver,
> > + * and the hardware. Commands that aren't supported by either the driver, or the
> > + * hardware are not returned in the query.
> > + *
> > + * Examples:
> > + *
> > + * - { .n_commands = 0 } // Get number of supported commands
> > + * - { .n_commands = 15, .commands = buf } // Return first 15 (or less)
> > + * supported commands
> > + *
> > + * See struct cxl_command_info.
> > + */
> > +struct cxl_mem_query_commands {
> > + /*
> > + * Input: Number of commands to return (space allocated by user)
> > + * Output: Number of commands supported by the driver/hardware
> > + *
> > + * If n_commands is 0, kernel will only return number of commands and
> > + * not try to populate commands[], thus allowing userspace to know how
> > + * much space to allocate
> > + */
>
> This is fairly well described in the docs above the structure.
> Perhaps combine the two.
>
> > + __u32 n_commands;
> > + __u32 rsvd;
> > +
> > + struct cxl_command_info __user commands[]; /* out: supported commands */
> > +};
> > +
> > +/**
> > + * struct cxl_send_command - Send a command to a memory device.
> > + * @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).
> > + * @rsvd: Must be zero.
> > + * @retval: Return value from the memory device (output).
> > + * @in.size: Size of the payload to provide to the device (input).
> > + * @in.rsvd: Must be zero.
> > + * @in.payload: Pointer to memory for payload input, payload is little endian.
> > + * @out.size: Size of the payload received from the device (input/output). This
> > + * field is filled in by userspace to let the driver know how much
> > + * space was allocated for output. It is populated by the driver to
> > + * let userspace know how large the output payload actually was.
> > + * @out.rsvd: Must be zero.
> > + * @out.payload: Pointer to memory for payload output, payload is little endian.
> > + *
> > + * Mechanism for userspace to send a command to the hardware for processing. The
> > + * driver will do basic validation on the command sizes. In some cases even the
> > + * payload may be introspected. Userspace is required to allocate large enough
> > + * buffers for size_out which can be variable length in certain situations.
> > + */
> > +struct cxl_send_command {
> > + __u32 id;
> > + __u32 flags;
> > + __u32 rsvd;
> > + __u32 retval;
> > +
> > + struct {
> > + __s32 size;
> > + __u32 rsvd;
> > + __u64 payload;
> > + } in;
> > +
> > + struct {
> > + __s32 size;
> > + __u32 rsvd;
> > + __u64 payload;
> > + } out;
> > +};
> > +
> > +#endif
>