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

From: Maximilian Luz
Date: Wed Mar 08 2023 - 09:01:38 EST


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