ATA Trusted commands in Linux

Question

Colleagues,

I'm implementing support for ATA trusted commands

0x5C, TRUSTED RECEIVE, 
0x5D, TRUSTED RECEIVE DMA, 
0x5E, TRUSTED SEND
0x5F, TRUSTED SEND DMA, 

for Linux (two hosts, Fedora 12 and 14) to support self-encrypting drives. I took a code from this page http://www.jukie.net/bart/blog/ata-via-scsi as the base code. For trusted receive (on this layer it is identical to IDENTIFY, 0xEC):

sg_io.interface_id    = 'S';
sg_io.cmdp            = cdb;
sg_io.cmd_len         = sizeof(cdb);
sg_io.dxferp          = data_in_buffer;
sg_io.dxfer_len       = data_in_length;         // multiple of 512
sg_io.dxfer_direction = SG_DXFER_FROM_DEV;
sg_io.sbp             = sense;
sg_io.mx_sb_len       = sizeof(sense);
sg_io.timeout         = 5000;                   // 5 seconds


cdb[0] = 0x85;           // pass-through ATA16 command (no translation)
cdb[1] = (4 << 1);       // data-in
cdb[2] = 0x2e;           // data-in
cdb[4] = feature_id;     // ATA feature ID
cdb[6] = 1;              // number of sectors
cdb[7] = lba_low >> 8;
cdb[8] = lba_low;
cdb[9] = lba_mid >> 8;
cdb[10] = lba_mid;
cdb[11] = lba_high >> 8;
cdb[12] = lba_high;
cdb[14] = 0x5C;           // TRUSTED RECEIVE

rc = ioctl (fd, SG_IO, &sg_io);

It works perfectly for Identify and all other commands, but not for trusted commands. When I connect protocol analyzer, I see that these commands are not sent to SATA bus. The adaptor is capable to send them, because they are coming OK under Windows (not my code, but I think using ATA_PASS_THROUGH). And yes, I'm running this code as root.

Please help to resolve this mystery :)

Answer 1

See /usr/src/linux/drivers/ata/libata-scsi.c:

/*
 * 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;