Re: [PATCH 9/9] vtpmmgr: Support GetRandom passthrough on TPM 2.0

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

Jason Andryuk, le mar. 04 mai 2021 08:48:42 -0400, a ecrit:
> GetRandom passthrough currently fails when using vtpmmgr with a hardware
> TPM 2.0.
> vtpmmgr (8): INFO[VTPM]: Passthrough: TPM_GetRandom
> vtpm (12): vtpm_cmd.c:120: Error: TPM_GetRandom() failed with error code (30)
> 
> When running on TPM 2.0 hardware, vtpmmgr needs to convert the TPM 1.2
> TPM_ORD_GetRandom into a TPM2 TPM_CC_GetRandom command.  Besides the
> differing ordinal, the TPM 1.2 uses 32bit sizes for the request and
> response (vs. 16bit for TPM2).
> 
> Place the random output directly into the tpmcmd->resp and build the
> packet around it.  This avoids bouncing through an extra buffer, but the
> header has to be written after grabbing the random bytes so we have the
> number of bytes to include in the size.
> 
> Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
> ---
>  stubdom/vtpmmgr/marshal.h          | 10 +++++++
>  stubdom/vtpmmgr/vtpm_cmd_handler.c | 48 ++++++++++++++++++++++++++++++
>  2 files changed, 58 insertions(+)
> 
> diff --git a/stubdom/vtpmmgr/marshal.h b/stubdom/vtpmmgr/marshal.h
> index dce19c6439..20da22af09 100644
> --- a/stubdom/vtpmmgr/marshal.h
> +++ b/stubdom/vtpmmgr/marshal.h
> @@ -890,6 +890,15 @@ inline int sizeof_TPM_AUTH_SESSION(const TPM_AUTH_SESSION* auth) {
>  	return rv;
>  }
>  
> +static
> +inline int sizeof_TPM_RQU_HEADER(BYTE* ptr) {
> +	int rv = 0;
> +	rv += sizeof_UINT16(ptr);
> +	rv += sizeof_UINT32(ptr);
> +	rv += sizeof_UINT32(ptr);
> +	return rv;
> +}
> +
>  static
>  inline BYTE* pack_TPM_RQU_HEADER(BYTE* ptr,
>  		TPM_TAG tag,
> @@ -923,5 +932,6 @@ inline int unpack3_TPM_RQU_HEADER(BYTE* ptr, UINT32* pos, UINT32 max,
>  #define pack_TPM_RSP_HEADER(p, t, s, r) pack_TPM_RQU_HEADER(p, t, s, r)
>  #define unpack_TPM_RSP_HEADER(p, t, s, r) unpack_TPM_RQU_HEADER(p, t, s, r)
>  #define unpack3_TPM_RSP_HEADER(p, l, m, t, s, r) unpack3_TPM_RQU_HEADER(p, l, m, t, s, r)
> +#define sizeof_TPM_RSP_HEADER(p) sizeof_TPM_RQU_HEADER(p)
>  
>  #endif
> diff --git a/stubdom/vtpmmgr/vtpm_cmd_handler.c b/stubdom/vtpmmgr/vtpm_cmd_handler.c
> index 2ac14fae77..7ca1d9df94 100644
> --- a/stubdom/vtpmmgr/vtpm_cmd_handler.c
> +++ b/stubdom/vtpmmgr/vtpm_cmd_handler.c
> @@ -47,6 +47,7 @@
>  #include "vtpm_disk.h"
>  #include "vtpmmgr.h"
>  #include "tpm.h"
> +#include "tpm2.h"
>  #include "tpmrsa.h"
>  #include "tcg.h"
>  #include "mgmt_authority.h"
> @@ -772,6 +773,52 @@ static int vtpmmgr_permcheck(struct tpm_opaque *opq)
>  	return 1;
>  }
>  
> +TPM_RESULT vtpmmgr_handle_getrandom(struct tpm_opaque *opaque,
> +				    tpmcmd_t* tpmcmd)
> +{
> +	TPM_RESULT status = TPM_SUCCESS;
> +	TPM_TAG tag;
> +	UINT32 size;
> +	UINT32 rand_offset;
> +	UINT32 rand_size;
> +	TPM_COMMAND_CODE ord;
> +	BYTE *p;
> +
> +	p = unpack_TPM_RQU_HEADER(tpmcmd->req, &tag, &size, &ord);
> +
> +	if (!hw_is_tpm2()) {
> +		size = TCPA_MAX_BUFFER_LENGTH;
> +		TPMTRYRETURN(TPM_TransmitData(tpmcmd->req, tpmcmd->req_len,
> +					      tpmcmd->resp, &size));
> +		tpmcmd->resp_len = size;
> +
> +		return TPM_SUCCESS;
> +	}


We need to check for the size of the request before unpacking (which
doesn't check for it), don't we?

> +	/* TPM_GetRandom req: <header><uint32 num bytes> */
> +	unpack_UINT32(p, &rand_size);
> +
> +	/* Call TPM2_GetRandom but return a TPM_GetRandom response. */
> +	/* TPM_GetRandom resp: <header><uint32 num bytes><num random bytes> */
> +        rand_offset = sizeof_TPM_RSP_HEADER(tpmcmd->resp) +
> +		      sizeof_UINT32(tpmcmd->resp);

There is a spurious indentation here, at first sight I even thought it
was part of the comment.


We also need to check that rand_size is not too large?
- that the returned data won't overflow tpmcmd->resp + rand_offset
- that it fits in a UINT16

Also, TPM2_GetRandom casts bytesRequested into UINT16*, that's bogus, it
should use a local UINT16 variable and assign *bytesRequested.

> +	TPMTRYRETURN(TPM2_GetRandom(&rand_size, tpmcmd->resp + rand_offset));
> +
> +	p = pack_TPM_RSP_HEADER(tpmcmd->resp, TPM_TAG_RSP_COMMAND,
> +				rand_offset + rand_size, status);
> +	p = pack_UINT32(p, rand_size);
> +	tpmcmd->resp_len = rand_offset + rand_size;
> +
> +	return status;
> +
> +abort_egress:
> +	tpmcmd->resp_len = VTPM_COMMAND_HEADER_SIZE;
> +	pack_TPM_RSP_HEADER(tpmcmd->resp, tag + 3, tpmcmd->resp_len, status);
> +
> +	return status;
> +}
> +
>  TPM_RESULT vtpmmgr_handle_cmd(
>  		struct tpm_opaque *opaque,
>  		tpmcmd_t* tpmcmd)
> @@ -842,6 +889,7 @@ TPM_RESULT vtpmmgr_handle_cmd(
>  		switch(ord) {
>  		case TPM_ORD_GetRandom:
>  			vtpmloginfo(VTPM_LOG_VTPM, "Passthrough: TPM_GetRandom\n");
> +			return vtpmmgr_handle_getrandom(opaque, tpmcmd);
>  			break;

Drop the break, then. I would say also move (or drop) the log, like the
other cases.

>  		case TPM_ORD_PcrRead:
>  			vtpmloginfo(VTPM_LOG_VTPM, "Passthrough: TPM_PcrRead\n");
> -- 
> 2.30.2
>