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

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