[Xen-devel] [PATCH v4 04/10] xen/arm: optee: add fast calls handling

[Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>]

From: Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx>

Some fast SMCCC calls to OP-TEE should be handled in a special way.
Capabilities exchange should be filtered out, so only caps
known to mediator are used. Also mediator disables static SHM
memory capability, because it can't share OP-TEE memory with a domain.
Only domain can share memory with OP-TEE, so it ensures that OP-TEE
supports dynamic SHM.

Basically, static SHM is a reserved memory region which is always
mapped into OP-TEE address space. It belongs to OP-TEE. Normally,
NW is allowed to access there, so it can communicate with OP-TEE.

On other hand, dynamic SHM is NW's own memory, which it can share
with OP-TEE. OP-TEE maps this memory dynamically, when it wants to
access it.

Because mediator can't share one static SHM region with all guests, it
just disables it for all of them. It is possible to make exception for
Dom0, and it will be done in a separate patch.

Signed-off-by: Volodymyr Babchuk <vlad.babchuk@xxxxxxxxx>
---

 All the patches to optee.c should be merged together. They were
 split to ease up review. But they depend heavily on each other.

Changes from v2:
  - Defined known capabilities explicitly
  - Fixed code style
---
 xen/arch/arm/tee/optee.c | 57 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 55 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
index b50c581aaf..61554ea191 100644
--- a/xen/arch/arm/tee/optee.c
+++ b/xen/arch/arm/tee/optee.c
@@ -24,6 +24,11 @@
 /* Client ID 0 is reserved for hypervisor itself */
 #define OPTEE_CLIENT_ID(domain) ((domain)->domain_id + 1)
 
+#define OPTEE_KNOWN_NSEC_CAPS OPTEE_SMC_NSEC_CAP_UNIPROCESSOR
+#define OPTEE_KNOWN_SEC_CAPS (OPTEE_SMC_SEC_CAP_HAVE_RESERVED_SHM | \
+                              OPTEE_SMC_SEC_CAP_UNREGISTERED_SHM | \
+                              OPTEE_SMC_SEC_CAP_DYNAMIC_SHM)
+
 static bool optee_probe(void)
 {
     struct dt_device_node *node;
@@ -99,6 +104,18 @@ static void forward_call(struct cpu_user_regs *regs)
     set_user_reg(regs, 7, 0);
 }
 
+static void set_return(struct cpu_user_regs *regs, uint32_t ret)
+{
+    set_user_reg(regs, 0, ret);
+    set_user_reg(regs, 1, 0);
+    set_user_reg(regs, 2, 0);
+    set_user_reg(regs, 3, 0);
+    set_user_reg(regs, 4, 0);
+    set_user_reg(regs, 5, 0);
+    set_user_reg(regs, 6, 0);
+    set_user_reg(regs, 7, 0);
+}
+
 static int optee_relinquish_resources(struct domain *d)
 {
     return 0;
@@ -124,6 +141,37 @@ static void optee_domain_destroy(struct domain *d)
                   &resp);
 }
 
+static void handle_exchange_capabilities(struct cpu_user_regs *regs)
+{
+    uint32_t caps;
+
+    /* Filter out unknown guest caps */
+    caps = get_user_reg(regs, 1);
+    caps &= OPTEE_KNOWN_NSEC_CAPS;
+    set_user_reg(regs, 1, caps);
+
+    forward_call(regs);
+    if ( get_user_reg(regs, 0) != OPTEE_SMC_RETURN_OK )
+        return;
+
+    caps = get_user_reg(regs, 1);
+
+    /* Filter out unknown OP-TEE caps */
+    caps &= OPTEE_KNOWN_SEC_CAPS;
+
+    /* Drop static SHM_RPC cap */
+    caps &= ~OPTEE_SMC_SEC_CAP_HAVE_RESERVED_SHM;
+
+    /* Don't allow guests to work without dynamic SHM */
+    if ( !(caps & OPTEE_SMC_SEC_CAP_DYNAMIC_SHM) )
+    {
+        set_return(regs, OPTEE_SMC_RETURN_ENOTAVAIL);
+        return;
+    }
+
+    set_user_reg(regs, 1, caps);
+}
+
 static bool optee_handle_call(struct cpu_user_regs *regs)
 {
     if ( !current->domain->arch.tee )
@@ -138,12 +186,17 @@ static bool optee_handle_call(struct cpu_user_regs *regs)
     case OPTEE_SMC_FUNCID_GET_OS_REVISION:
     case OPTEE_SMC_ENABLE_SHM_CACHE:
     case OPTEE_SMC_DISABLE_SHM_CACHE:
-    case OPTEE_SMC_GET_SHM_CONFIG:
-    case OPTEE_SMC_EXCHANGE_CAPABILITIES:
     case OPTEE_SMC_CALL_WITH_ARG:
     case OPTEE_SMC_CALL_RETURN_FROM_RPC:
         forward_call(regs);
         return true;
+    case OPTEE_SMC_GET_SHM_CONFIG:
+        /* No static SHM available for guests */
+        set_return(regs, OPTEE_SMC_RETURN_ENOTAVAIL);
+        return true;
+    case OPTEE_SMC_EXCHANGE_CAPABILITIES:
+        handle_exchange_capabilities(regs);
+        return true;
     default:
         return false;
     }
-- 
2.21.0

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel