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>

1 files changed, 18 insertions, 0 deletions

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;