libata: Disable ATA8-ACS proposed Trusted Computing features by default

Historically word 48 in the identify data was used to mean 32bit I/O
was supported for VLB IDE etc. ATA8 reassigns this word to the Trusted
Computing Group, where it is used for TCG features. This means that
an ATA8 TCG drive is going to trigger 32bit I/O on some systems which
will be funny.

Anyway we need to sort this out ready for ATA8 so:
- Reorder the ata.h header a bit so the ata_version function occurs early
  in it
- Make dword_io check the ATA version
- Add an ATA8 version checking TCG presence test

While we are at it the current drafts have a flaw where it may not be
possible to disable TCG features at boot (and opt out of the trusted
model) as TCG intends because it relies on presence of a different
optional feature (DCS). Handle this in software by refusing the TCG
commands if libata.allow_tpm is not set. (We must make it possible
as some environments such as proprietary VDR devices will doubtless
want to use it to lock up content)

Finally as with CPRM print a warning so that the user knows they may
not be able to full access and use the device.

Signed-off-by: Alan Cox <alan@redhat.com>

4 files changed, 51 insertions, 2 deletions

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 6380726f7538..9b7f3c477730 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -119,6 +119,10 @@ int libata_noacpi = 0;
 module_param_named(noacpi, libata_noacpi, int, 0444);
 MODULE_PARM_DESC(noacpi, "Disables the use of ACPI in probe/suspend/resume when set");
 
+int libata_allow_tpm = 0;
+module_param_named(allow_tpm, libata_allow_tpm, int, 0444);
+MODULE_PARM_DESC(allow_tpm, "Permit the use of TPM commands");
+
 MODULE_AUTHOR("Jeff Garzik");
 MODULE_DESCRIPTION("Library module for ATA devices");
 MODULE_LICENSE("GPL");
@@ -2161,8 +2165,14 @@ int ata_dev_configure(struct ata_device *dev)
                                                "supports DRM functions and may "
                                                "not be fully accessable.\n");
                         snprintf(revbuf, 7, "CFA");
-                } else
+                } else {
                         snprintf(revbuf, 7, "ATA-%d", ata_id_major_version(id));
+                        /* Warn the user if the device has TPM extensions */
+                        if (ata_id_has_tpm(id))
+                                ata_dev_printk(dev, KERN_WARNING,
+                                               "supports DRM functions and may "
+                                               "not be fully accessable.\n");
+                }
 
                 dev->n_sectors = ata_id_n_sectors(id);
 
diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
index 14daf4848f09..f802dbce41ae 100644
--- a/drivers/ata/libata-scsi.c
+++ b/drivers/ata/libata-scsi.c
@@ -2690,6 +2690,24 @@ static unsigned int ata_scsi_pass_thru(struct ata_queued_cmd *qc)
         if ((tf->protocol = ata_scsi_map_proto(cdb[1])) == ATA_PROT_UNKNOWN)
                 goto invalid_fld;
 
+        /*
+         * Filter TPM commands by default. These provide an
+         * essentially uncontrolled encrypted "back door" between
+         * applications and the disk. Set libata.allow_tpm=1 if you
+         * have a real reason for wanting to use them. This ensures
+         * that installed software cannot easily mess stuff up without
+         * user intent. DVR type users will probably ship with this enabled
+         * for movie content management.
+         *
+         * Note that for ATA8 we can issue a DCS change and DCS freeze lock
+         * for this and should do in future but that it is not sufficient as
+         * DCS is an optional feature set. Thus we also do the software filter
+         * so that we comply with the TC consortium stated goal that the user
+         * can turn off TC features of their system.
+         */
+        if (tf->command >= 0x5C && tf->command <= 0x5F && !libata_allow_tpm)
+                goto invalid_fld;
+
         /* We may not issue DMA commands if no DMA mode is set */
         if (tf->protocol == ATA_PROT_DMA && dev->dma_mode == 0)
                 goto invalid_fld;
diff --git a/drivers/ata/libata.h b/drivers/ata/libata.h
index bbe59c2fd1e2..048e26cfb339 100644
--- a/drivers/ata/libata.h
+++ b/drivers/ata/libata.h
@@ -60,6 +60,7 @@ extern int atapi_dmadir;
 extern int atapi_passthru16;
 extern int libata_fua;
 extern int libata_noacpi;
+extern int libata_allow_tpm;
 extern struct ata_queued_cmd *ata_qc_new_init(struct ata_device *dev);
 extern int ata_build_rw_tf(struct ata_taskfile *tf, struct ata_device *dev,
                            u64 block, u32 n_block, unsigned int tf_flags,
diff --git a/include/linux/ata.h b/include/linux/ata.h
index e672e80202a8..3fbe6d7784ab 100644
--- a/include/linux/ata.h
+++ b/include/linux/ata.h
@@ -379,7 +379,6 @@ struct ata_taskfile {
 #define ata_id_has_ncq(id)      ((id)[76] & (1 << 8))
 #define ata_id_queue_depth(id)  (((id)[75] & 0x1f) + 1)
 #define ata_id_removeable(id)   ((id)[0] & (1 << 7))
-#define ata_id_has_dword_io(id) ((id)[48] & (1 << 0))
 #define ata_id_has_atapi_AN(id) \
         ( (((id)[76] != 0x0000) && ((id)[76] != 0xffff)) && \
           ((id)[78] & (1 << 5)) )
@@ -415,6 +414,7 @@ static inline bool ata_id_has_dipm(const u16 *id)
         return val & (1 << 3);
 }
 
+
 static inline int ata_id_has_fua(const u16 *id)
 {
         if ((id[84] & 0xC000) != 0x4000)
@@ -519,6 +519,26 @@ static inline int ata_id_is_sata(const u16 *id)
         return ata_id_major_version(id) >= 5 && id[93] == 0;
 }
 
+static inline int ata_id_has_tpm(const u16 *id)
+{
+        /* The TPM bits are only valid on ATA8 */
+        if (ata_id_major_version(id) < 8)
+                return 0;
+        if ((id[48] & 0xC000) != 0x4000)
+                return 0;
+        return id[48] & (1 << 0);
+}
+
+static inline int ata_id_has_dword_io(const u16 *id)
+{
+        /* ATA 8 reuses this flag for "trusted" computing */
+        if (ata_id_major_version(id) > 7)
+                return 0;
+        if (id[48] & (1 << 0))
+                return 1;
+        return 0;
+}
+
 static inline int ata_id_current_chs_valid(const u16 *id)
 {
         /* For ATA-1 devices, if the INITIALIZE DEVICE PARAMETERS command