Re: [PATCH 13/14] cxl/mem: Add limited Get Log command (0401h)

Konrad Rzeszutek Wilk
2021-02-01T18:31:32Z

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
>