You are of course correct. The TPM is a slave device and certainly
can't go out on the bus and read memory.
You can locally store the bytes any way you like, as an array or as a
pointer to an array. So can the TPM. When you marshal/serialize the
structure, the result must be the bit map, not a pointer to a bitmap.
This is explained at the beginning of the document:
~~~~~~
2.1.6 Structure Definitions
This is not a MIDL compatible specification. The syntax of a structure
definition is just a hint. It should be used with Description column to
determine the nature of a structure member.
4. BYTE* is an array of bytes whose length is specified by a previous
structure member. The array is not present if the length is zero.
~~~~~~
and the description of the pcrSelect is:
"This SHALL be a bit map that indicates if a PCR is active or not"
It is NOT "a C language pointer to a bitmap"
On 3/2/2014 6:21 PM, Robert Sutton II wrote:
>
> typedef struct tdTPM_PCR_SELECTION {
> UINT16 sizeOfSelect;
> [size_is(sizeOfSelect)] BYTE* pcrSelect;
> } TPM_PCR_SELECTION;
>
> Is pcrSelect really a pointer into memory? This seems really odd. So
> when I save pcrSelect on my stack and pass the pointer to the TPM, does
> this mean the TPM is reading pcrSelect off my stack? Why not just
> include the bytes directly in the structure, instead of a pointer to
> memory? This makes more sense because pcrSelect will never be more than
> a couple of bytes. I honestly didn't even know the TPM could read
> directly from memory like that.
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