[SLOF] [PATCH v3 2/2] tpm: Implement firmware API call pass-through-to-tpm

[Stefan Berger]

On 10/31/24 9:52 PM, Alexey Kardashevskiy wrote:
> 
> 
> On Tue, 29 Oct 2024, at 23:49, Stefan Berger wrote:
>> From: Stefan Berger <stefanb at linux.ibm.com>
>>
>> Implement the firmware API call pass-through-to-tpm that allows a caller
>> to pass a TPM command to the TPM. Since the buffer provided by the user
>> will be used for returning the TPM's response it must be sufficiently
>> large. To be safe, it should be of the size returned by the firmware API
>> call tpm-get-maximum-cmd-size.
>>
>> Signed-off-by: Stefan Berger <stefanb at linux.ibm.com>
>> ---
>> board-qemu/slof/vio-vtpm-cdriver.fs | 11 +++++++++++
>> lib/libtpm/tcgbios.c                | 25 +++++++++++++++++++++++++
>> lib/libtpm/tcgbios.h                |  1 +
>> lib/libtpm/tpm.code                 | 11 +++++++++++
>> lib/libtpm/tpm.in                   |  1 +
>> 5 files changed, 49 insertions(+)
>>
>> diff --git a/board-qemu/slof/vio-vtpm-cdriver.fs b/board-qemu/slof/vio-vtpm-cdriver.fs
>> index 21c2190..ced2ac0 100644
>> --- a/board-qemu/slof/vio-vtpm-cdriver.fs
>> +++ b/board-qemu/slof/vio-vtpm-cdriver.fs
>> @@ -57,6 +57,17 @@ LOG-SIZE BUFFER: log-base
>>       THEN
>> ;
>>   
>> +\ firmware API call
>> +: pass-through-to-tpm ( buf-addr cmd-size -- rsp-size )
>> +    vtpm-debug? IF
>> +        ." Call to pass-through-to-tpm" cr
>> +    THEN
>> +    tpm-pass-through-to-tpm                ( rsp-size )
>> +    vtpm-debug? IF
>> +        ." VTPM: tpm-pass-through-to-tpm returned size: " dup . cr
>> +    THEN
>> +;
>> +
>> \ firmware API call
>> : get-maximum-cmd-size ( -- max-size )
>>       vtpm-debug? IF
>> diff --git a/lib/libtpm/tcgbios.c b/lib/libtpm/tcgbios.c
>> index a64afde..366eda9 100644
>> --- a/lib/libtpm/tcgbios.c
>> +++ b/lib/libtpm/tcgbios.c
>> @@ -972,6 +972,31 @@ uint32_t tpm_get_maximum_cmd_size(void)
>> return PAPR_VTPM_MAX_BUFFER_SIZE;
>> }
>>   
>> +uint32_t tpm_pass_through_to_tpm(void *buffer, uint32_t cmd_size)
>> +{
>> + unsigned char respbuffer[PAPR_VTPM_MAX_BUFFER_SIZE];
>> + uint32_t respbufferlen = sizeof(respbuffer);
>> + struct tpm_req_header *hdr = buffer;
>> + uint32_t totlen;
> 
> uint32_t totlen = be32_to_cpu(hdr->totlen);
> and drop memcpy(&totlen,...) below?

I did this not wanting to assume alignment.

> 
>> + int ret;
> 
> A nit: not really needed, could do "if (spapr_transmit())"
> (only because I am commenting on other things)
> 
>> +
>> + if (cmd_size < sizeof(struct tpm_req_header))
>> + return 0;
>> +
>> + memcpy(&totlen, &hdr->totlen, sizeof(totlen));
>> + if (cmd_size != be32_to_cpu(totlen))
> 
> So the caller has to pass the length twice - in @buffer (==header) and in @cmd_size, can we drop @cmd_size?

cmd_size is redundant.

> Is it a total size of the buffer (and then passing @cmd_size makes sense but checking cmd_size!=totlen does not) or a size of a TPM command (looks like this is the case but then this function does not know if @buffer is big enough for the response)?

The spec says: "The method takes as arguments the address and size of a 
fully formed TPM command – which is passed to the vTPM. The entire 
response is copied back over the input buffer – which must be large 
enough to accept the expected response or else the buffer will be overrun ."

> 
>> + return 0;
>> +
>> + ret = spapr_transmit(0, buffer, respbuffer, &respbufferlen,
>> +      TPM_DURATION_TYPE_LONG);
>> + if (ret)
>> + return 0;
>> +
>> + memcpy(buffer, respbuffer, respbufferlen);
> 
> This assumes @buffer has enough space and respbufferlen<=cmd_size but does not check for this.
> Probably may be also worth checking if the returned hdr->totlen not out of boundaries too, or the returned buffer does not have a header? Thanks,

See quote from spec.