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

[Jason Andryuk <jandryuk@gmail.com>]

On Tue, May 4, 2021 at 9:33 AM Samuel Thibault
<samuel.thibault@ens-lyon.org> wrote:
>
> 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?

Yes, good catch.  vtpmmgr_handle_cmd doesn't check either.

> > +     /* 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.

Sorry about that - it was 8 spaces instead of a tab.

> 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

Yes, will do.

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

Good catch.  I'll do that in a new patch.

> > +     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.

Will drop the break.  I would just leave the log since it matches the
other cases in this case statement.  But I can remove it if you want.

Regards,
Jason