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

Ben Widawsky
2021-02-02T23:52:05Z

On 21-02-01 13:28:48, Konrad Rzeszutek Wilk wrote:
> 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?
>

The commit message needs update btw as CEL is allowed in the latest rev of the
patches.

We could potentially combine this with the now added (in a branch) CONFIG_RAW
config option. Indeed I think that makes sense. Dan, thoughts?

> >
> > 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
> >