Re: [PATCH v3 2/4] firmware: Add support for Qualcomm Secure Execution Environment SCM interface

[Maximilian Luz]

On 3/7/23 16:32, Dmitry Baryshkov wrote:
> On 05/03/2023 04:21, Maximilian Luz wrote:

[...]

> > +/* -- DMA helpers. ---------------------------------------------------------- */
> > +
> > +/* DMA requirements for QSEECOM SCM calls. */
> > +#define QSEECOM_DMA_ALIGNMENT        8
> > +#define QSEECOM_DMA_ALIGN(ptr)        ALIGN(ptr, QSEECOM_DMA_ALIGNMENT)
> > +
> > +/**
> > + * struct qseecom_dma - DMA memory region.
> > + * @size: Size of the memory region, in bytes.
> > + * @virt: Pointer / virtual address to the memory, accessible by the kernel.
> > + * @phys: Physical address of the memory region.
> > + */
> > +struct qseecom_dma {
> > +    unsigned long size;
>
> size_t ?

Will fix.

> > +    void *virt;
> > +    dma_addr_t phys;
> > +};
>
> Do we really need this wrapper and the wrappers bellow? They look like a pure syntax sugar for me, hiding the dma functions from the user.

The idea was that they take care of proper allocation. The Windows driver that
I've reverse-engineered this from allocates memory in multiples of PAGE_SIZE,
so I believe that this might be a requirement (at least on some systems). These
functions are there to ensure that and with that prevent potential bugs by
taking that responsibility from the caller.

> > +
> > +/**
> > + * qseecom_dma_alloc() - Allocate a DMA-able memory region suitable for QSEECOM
> > + * SCM calls.
> > + * @dev:  The device used for DMA memory allocation.
> > + * @dma:  Where to write the allocated memory addresses and size to.
> > + * @size: Minimum size of the memory to be allocated.
> > + * @gfp:  Flags used for allocation.
> > + *
> > + * Allocate a DMA-able memory region suitable for interaction with SEE
> > + * services/applications and the TzOS. The provided size is treated as the
> > + * minimum required size and rounded up, if necessary. The actually allocated
> > + * memory region will be stored in @dma. Allocated memory must be freed via
> > + * qseecom_dma_free().
> > + *
> > + * Return: Returns zero on success, -ENOMEM on allocation failure.
> > + */
> > +static inline int qseecom_dma_alloc(struct device *dev, struct qseecom_dma *dma,
> > +                    unsigned long size, gfp_t gfp)
>
> size_t size
>
> gfp is not used

Right, that should have been passed to dma_alloc_coherent(). Will fix that.

> > +{
> > +    size = PAGE_ALIGN(size);
> > +
> > +    dma->virt = dma_alloc_coherent(dev, size, &dma->phys, GFP_KERNEL);
> > +    if (!dma->virt)
> > +        return -ENOMEM;
> > +
> > +    dma->size = size;
> > +    return 0;
> > +}
> > +
> > +/**
> > + * qseecom_dma_free() - Free a DMA memory region.
> > + * @dev: The device used for allocation.
> > + * @dma: The DMA region to be freed.
> > + *
> > + * Free a DMA region previously allocated via qseecom_dma_alloc(). Note that
> > + * freeing sub-regions is not supported.
> > + */
> > +static inline void qseecom_dma_free(struct device *dev, struct qseecom_dma *dma)
> > +{
> > +    dma_free_coherent(dev, dma->size, dma->virt, dma->phys);
> > +}
> > +
> > +/**
> > + * qseecom_dma_realloc() - Re-allocate DMA memory region with the requested size.
> > + * @dev:  The device used for allocation.
> > + * @dma:  The region descriptor to be updated.
> > + * @size: The new requested size.
> > + * @gfp:  Flags used for allocation.
> > + *
> > + * Re-allocates a DMA memory region suitable for QSEECOM SCM calls to fit the
> > + * requested amount of bytes, if necessary. Does nothing if the provided region
> > + * already has enough space to store the requested data.
> > + *
> > + * See qseecom_dma_alloc() for details.
> > + *
> > + * Return: Returns zero on success, -ENOMEM on allocation failure.
> > + */
> > +static inline int qseecom_dma_realloc(struct device *dev, struct qseecom_dma *dma,
> > +                      unsigned long size, gfp_t gfp)
> > +{
> > +    if (PAGE_ALIGN(size) <= dma->size)
> > +        return 0;
> > +
> > +    qseecom_dma_free(dev, dma);
> > +    return qseecom_dma_alloc(dev, dma, size, gfp);
> > +}
>
> I'll comment on this function when commenting patch 4.
>
> > +
> > +/**
> > + * qseecom_dma_aligned() - Create a aligned DMA memory sub-region suitable for
> > + * QSEECOM SCM calls.
> > + * @base:   Base DMA memory region, in which the new region will reside.
> > + * @out:    Descriptor to store the aligned sub-region in.
> > + * @offset: The offset inside base region at which to place the new sub-region.
> > + *
> > + * Creates an aligned DMA memory region suitable for QSEECOM SCM calls at or
> > + * after the given offset. The size of the sub-region will be set to the
> > + * remaining size in the base region after alignment, i.e., the end of the
> > + * sub-region will be equal the end of the base region.
> > + *
> > + * Return: Returns zero on success or -EINVAL if the new aligned memory address
> > + * would point outside the base region.
> > + */
> > +static inline int qseecom_dma_aligned(const struct qseecom_dma *base, struct qseecom_dma *out,
> > +                      unsigned long offset)
> > +{
> > +    void *aligned = (void *)QSEECOM_DMA_ALIGN((uintptr_t)base->virt + offset);
> > +
> > +    if (aligned - base->virt > base->size)
> > +        return -EINVAL;
> > +
> > +    out->virt = aligned;
> > +    out->phys = base->phys + (out->virt - base->virt);
> > +    out->size = base->size - (out->virt - base->virt);
> > +
> > +    return 0;
> > +}
> > +
> > +
> > +/* -- Common interface. ----------------------------------------------------- */
> > +
> > +struct qseecom_device {
> > +    struct device *dev;
> > +    struct mutex scm_call_lock;    /* Guards QSEECOM SCM calls. */
>
> There can be only one instance of the qseecom call infrastructure. Make this mutex static in the qcom_scm.c

Right, will do that.

> > +};
> > +
> > +
> > +/* -- Secure-OS SCM call interface. ----------------------------------------- */
> > +
> > +#define QSEECOM_TZ_OWNER_TZ_APPS        48
> > +#define QSEECOM_TZ_OWNER_QSEE_OS        50
> > +
> > +#define QSEECOM_TZ_SVC_APP_ID_PLACEHOLDER    0
> > +#define QSEECOM_TZ_SVC_APP_MGR            1
> > +
> > +enum qseecom_scm_result {
> > +    QSEECOM_RESULT_SUCCESS            = 0,
> > +    QSEECOM_RESULT_INCOMPLETE        = 1,
> > +    QSEECOM_RESULT_BLOCKED_ON_LISTENER    = 2,
> > +    QSEECOM_RESULT_FAILURE            = 0xFFFFFFFF,
> > +};
> > +
> > +enum qseecom_scm_resp_type {
> > +    QSEECOM_SCM_RES_APP_ID            = 0xEE01,
> > +    QSEECOM_SCM_RES_QSEOS_LISTENER_ID    = 0xEE02,
> > +};
> > +
> > +/**
> > + * struct qseecom_scm_resp - QSEECOM SCM call response.
> > + * @status:    Status of the SCM call. See &enum qseecom_scm_result.
> > + * @resp_type: Type of the response. See &enum qseecom_scm_resp_type.
> > + * @data:      Response data. The type of this data is given in @resp_type.
> > + */
> > +struct qseecom_scm_resp {
> > +    u64 status;
> > +    u64 resp_type;
> > +    u64 data;
> > +};
> > +
> > +int qseecom_scm_call(struct qseecom_device *qsee, const struct qcom_scm_desc *desc,
> > +             struct qseecom_scm_resp *res);
> > +
> > +
> > +/* -- Secure App interface. ------------------------------------------------- */
> > +
> > +#define QSEECOM_MAX_APP_NAME_SIZE            64
> > +
> > +int qseecom_app_get_id(struct qseecom_device *qsee, const char *app_name, u32 *app_id);
> > +int qseecom_app_send(struct qseecom_device *qsee, u32 app_id, struct qseecom_dma *req,
> > +             struct qseecom_dma *rsp);
>
> I think that only these calls should be made public / available to other modules. qseecom_scm_call also is an internal helper.

So move all calls to qcom_scm and only make these two public? Or move only
qseecom_scm_call() to qcom_scm (which would require to make it public there,
however). Or how would you want this to look?

> > +
> > +#endif /* _LINUX_QCOM_QSEECOM_H */

Regards,
Max