Re: [PATCH v2 01/22] x86/include/asm/intel-txt.h: constants and accessors for TXT registers and heap

[Sergii Dmytruk <sergii.dmytruk@3mdeb.com>]

On Wed, May 21, 2025 at 05:19:57PM +0200, Jan Beulich wrote:
> > +/*
> > + * The same set of registers is exposed twice (with different permissions) and
> > + * they are allocated continuously with page alignment.
> > + */
> > +#define NR_TXT_CONFIG_SIZE \
> > +    (TXT_PUB_CONFIG_REGS_BASE - TXT_PRIV_CONFIG_REGS_BASE)
>
> What does the NR_ in the identifier try to express?

That's a leftover from the original name inside tboot.c, I'll rename it
to TXT_CONFIG_SPACE_SIZE.

> > +/*
> > + * Secure Launch defined OS/MLE TXT Heap table
> > + */
> > +struct txt_os_mle_data {
> > +    uint32_t version;
> > +    uint32_t reserved;
> > +    uint64_t slrt;
> > +    uint64_t txt_info;
> > +    uint32_t ap_wake_block;
> > +    uint32_t ap_wake_block_size;
> > +    uint8_t mle_scratch[64];
> > +} __packed;
>
> This being x86-specific, what's the __packed intended to achieve here?

This structure is passed to Xen by a bootloader, __packed makes sure the
structure has a compatible layout.

> > +/*
> > + * TXT specification defined BIOS data TXT Heap table
> > + */
> > +struct txt_bios_data {
> > +    uint32_t version; /* Currently 5 for TPM 1.2 and 6 for TPM 2.0 */
> > +    uint32_t bios_sinit_size;
> > +    uint64_t reserved1;
> > +    uint64_t reserved2;
> > +    uint32_t num_logical_procs;
> > +    /* Versions >= 3 && < 5 */
> > +    uint32_t sinit_flags;
> > +    /* Versions >= 5 with updates in version 6 */
> > +    uint32_t mle_flags;
> > +    /* Versions >= 4 */
> > +    /* Ext Data Elements */
> > +} __packed;
>
> It does affect sizeof() here, which I'm unsure is going to matter.

It doesn't hurt anything and makes sure offsets match those in the
specification.

> > +static inline uint64_t txt_bios_data_size(void *heap)
>
> Here, below, and in general: Please try to have code be const-correct, i.e.
> use pointers-to-const wherever applicable.

I assume this doesn't apply to functions returning `void *`.  The
approach used in libc is to accept pointers-to-const but then cast the
constness away for the return value, but this header isn't a widely-used
code.

> > +{
> > +    return *((uint64_t *)heap) - sizeof(uint64_t);
>
> For readability it generally helps if excess parentheses like the ones here
> are omitted.

OK.

> > +static inline uint64_t txt_os_mle_data_size(void *heap)
> > +{
> > +    return *((uint64_t *)(txt_bios_data_start(heap) +
> > +                          txt_bios_data_size(heap))) -
> > +        sizeof(uint64_t);
>
> This line wants indenting a little further, such that the"sizeof" aligns
> with the start of the expression. (Same elsewhere below.)
>
> Jan

Will update.

Regards