Re: [SeaBIOS] [RFC PATCH v1 6/9] tpm: Implement tpm2_prepboot

[Kevin O'Connor]

On Fri, Jan 15, 2016 at 02:44:36PM -0500, Stefan Berger wrote:
> From: Stefan Berger
>
> Implement tpm2_preboot.
>
> Here we set the platform password to a random password that prevents
> higher layers (OS) to get this password. This avoids bad things like users
> clearing the TPM, erasing EK (primary key) certificates, changing the
> primary key etc.
>
> The clearing of the TPM will still be possible through the TPM 2 menu.
> Signed-off-by: Stefan Berger
>
> src/std/tcg.h |  44 +++++++++++++++++++++++
>  src/tcgbios.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 152 insertions(+), 2 deletions(-)
>
> diff --git a/src/std/tcg.h b/src/std/tcg.h
> index db1155d..e0d6f30 100644
> --- a/src/std/tcg.h
> +++ b/src/std/tcg.h
> @@ -372,14 +372,58 @@ struct tpm_res_sha1complete {
>  #define TPM2_SU_CLEAR               0x0000
>  #define TPM2_SU_STATE               0x0001
>
> +#define TPM2_RS_PW                  0x40000009
> +#define TPM2_RH_PLATFORM            0x4000000c
>
> /* TPM 2 command tags */
>  #define TPM2_ST_NO_SESSIONS         0x8001
> +#define TPM2_ST_SESSIONS            0x8002
>
> /* TPM 2 commands */
> +#define TPM2_CC_HierarchyChangeAuth 0x129
>  #define TPM2_CC_SelfTest            0x143
>  #define TPM2_CC_Startup             0x144
> +#define TPM2_CC_StirRandom          0x146
> +#define TPM2_CC_GetRandom           0x17b
>
> /* TPM 2 error codes */
>  #define TPM2_RC_INITIALIZE          0x100
>
> +/* TPM 2 data structures */
>
> +struct tpm2b_stir {
> u16 size;
> u64 stir;
>
> +} PACKED;
>
> +struct tpm2_req_getrandom {
> struct tpm_req_header hdr;
> u16 bytesRequested;
>
> +} PACKED;
>
> +struct tpm2b_20 {
> u16 size;
> u8 buffer[20];
>
> +} PACKED;
>
> +struct tpm2_res_getrandom {
> struct tpm_rsp_header hdr;
> struct tpm2b_20 rnd;
>
> +} PACKED;
>
> +struct tpm2_authblock {
> u32 handle;
> u16 noncesize;  /* always 0 */
> u8 contsession; /* always TPM2_YES */
> u16 pwdsize;    /* always 0 */
>
> +} PACKED;
>
> +struct tpm2_req_hierarchychangeauth {
> struct tpm_req_header hdr;
> u32 authhandle;
> u32 authblocksize;
> struct tpm2_authblock authblock;
> struct tpm2b_20 newAuth;
>
> +} PACKED;
>
> #endif // tcg.h
> diff --git a/src/tcgbios.c b/src/tcgbios.c
> index 7b6409c..4f5c5bb 100644
> --- a/src/tcgbios.c
> +++ b/src/tcgbios.c
> @@ -204,7 +204,7 @@ tpm_build_and_send_cmd(u8 locty, u32 ordinal, const u8 *append,
>  {
>      struct {
>          struct tpm_req_header trqh;
>    u8 cmd[6];
>    u8 cmd[10];
> } PACKED req = {
>        .trqh.tag = cpu_to_be16(TPM_TAG_RQU_CMD),
>        .trqh.totlen = cpu_to_be32(sizeof(req.trqh) + append_size),
>
> @@ -654,6 +654,112 @@ tpm_setup(void)
>      tpm_add_action(2, "Start Option ROM Scan");
>  }
>
> +static int
> +tpm2_stirrandom(void)
> +{
> struct tpm2b_stir stir = {
>    .size = cpu_to_be16(sizeof(stir.stir)),
>    .stir = rdtscll(),
> };
> /* set more bits to stir with */
> stir.stir += swab64(rdtscll());
> return tpm_build_and_send_cmd(0, TPM2_CC_StirRandom,
>                              (u8 *)&stir, sizeof(stir),
>                              TPM_DURATION_TYPE_SHORT);
>
> +}
>
> +static int
> +tpm2_getrandom(u8 *buf, u16 buf_len)
> +{
> struct tpm2_res_getrandom rsp;
> if (buf_len > sizeof(rsp.rnd.buffer))
>    return -1;
> struct tpm2_req_getrandom trgr = {
>    .hdr.tag = cpu_to_be16(TPM2_ST_NO_SESSIONS),
>    .hdr.totlen = cpu_to_be32(sizeof(trgr)),
>    .hdr.ordinal = cpu_to_be32(TPM2_CC_GetRandom),
>    .bytesRequested = cpu_to_be16(buf_len),
> };
> u32 resp_length = sizeof(rsp);
> int ret = tpmhw_transmit(0, &trgr.hdr, &rsp, &resp_length,
>                         TPM_DURATION_TYPE_MEDIUM);
> if (ret || resp_length != sizeof(rsp) || rsp.hdr.errcode)
>    return -1;
> memcpy(buf, rsp.rnd.buffer, buf_len);
> return 0;
>
> +}
>
> +static int
> +tpm2_hierarchychangeauth(u8 auth[20])
> +{
> struct tpm2_req_hierarchychangeauth trhca = {
>    .hdr.tag = cpu_to_be16(TPM2_ST_SESSIONS),
>    .hdr.totlen = cpu_to_be32(sizeof(trhca)),
>    .hdr.ordinal = cpu_to_be32(TPM2_CC_HierarchyChangeAuth),
>    .authhandle = cpu_to_be32(TPM2_RH_PLATFORM),
>    .authblocksize = cpu_to_be32(sizeof(trhca.authblock)),
>    .authblock = {
>        .handle = cpu_to_be32(TPM2_RS_PW),
>        .noncesize = cpu_to_be16(0),
>        .contsession = TPM2_YES,
>        .pwdsize = cpu_to_be16(0),
>    },
>    .newAuth = {
>        .size = cpu_to_be16(sizeof(trhca.newAuth.buffer)),
>    },
> };
> memcpy(trhca.newAuth.buffer, auth, sizeof(trhca.newAuth.buffer));
> struct tpm_rsp_header rsp;
> u32 resp_length = sizeof(rsp);
> int ret = tpmhw_transmit(0, &trhca.hdr, &rsp, &resp_length,
>                         TPM_DURATION_TYPE_MEDIUM);
> if (ret || resp_length != sizeof(rsp) || rsp.errcode)
>    return -1;
> return 0;
>
> +}
>
> +static void
> +tpm2_prepboot(void)
> +{
> int ret = tpm2_stirrandom();
> dprintf(DEBUG_tcg, "TCGBIOS: Return value from sending TPM2_StirRandom = 0x%08x\n",
>        ret);
> if (ret)
>     goto err_exit;
> u8 auth[20];
> ret = tpm2_getrandom(&auth[0], sizeof(auth));
> dprintf(DEBUG_tcg, "TCGBIOS: Return value from sending TPM2_GetRandom = 0x%08x\n",
>        ret);
> if (ret)
>    goto err_exit;
> ret = tpm2_hierarchychangeauth(auth);
> dprintf(DEBUG_tcg, "TCGBIOS: Return value from sending TPM2_HierarchyChangeAuth = 0x%08x\n",
>        ret);

Minor nit - I think it would be better for an error dprintf to be done
in the function that raised the error instead of the callers of that
function.

-Kevin