[Xen-devel] [PATCH v2 05/13] optee: add fast calls handling

[Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>]

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.

Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
---
 xen/arch/arm/tee/optee.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 55 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
index 7bb84d9..48bff5d 100644
--- a/xen/arch/arm/tee/optee.c
+++ b/xen/arch/arm/tee/optee.c
@@ -56,7 +56,7 @@ static int optee_enable(struct domain *d)
     return 0;
 }
 
-static void forward_call(struct cpu_user_regs *regs)
+static bool forward_call(struct cpu_user_regs *regs)
 {
     struct arm_smccc_res resp;
 
@@ -79,6 +79,20 @@ static void forward_call(struct cpu_user_regs *regs)
     set_user_reg(regs, 5, 0);
     set_user_reg(regs, 6, 0);
     set_user_reg(regs, 7, 0);
+
+    return resp.a0 == OPTEE_SMC_RETURN_OK;
+}
+
+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 void optee_domain_destroy(struct domain *d)
@@ -92,6 +106,39 @@ static void optee_domain_destroy(struct domain *d)
                   &resp);
 }
 
+static bool handle_exchange_capabilities(struct cpu_user_regs *regs)
+{
+    uint32_t caps;
+
+    /* Filter out unknown guest caps */
+    caps = get_user_reg(regs, 1);
+    caps &= OPTEE_SMC_NSEC_CAP_UNIPROCESSOR;
+    set_user_reg(regs, 1, caps);
+
+    /* Forward call and return error (if any) back to the guest */
+    if ( !forward_call(regs) )
+        return true;
+
+    caps = get_user_reg(regs, 1);
+
+    /* Filter out unknown OP-TEE caps */
+    caps &= OPTEE_SMC_SEC_CAP_HAVE_RESERVED_SHM |
+        OPTEE_SMC_SEC_CAP_UNREGISTERED_SHM |
+        OPTEE_SMC_SEC_CAP_DYNAMIC_SHM;
+
+    /* 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 true;
+    }
+
+    set_user_reg(regs, 1, caps);
+    return true;
+}
+
 static bool optee_handle_call(struct cpu_user_regs *regs)
 {
     switch ( get_user_reg(regs, 0) )
@@ -103,10 +150,17 @@ 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:
+        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:
+        return handle_exchange_capabilities(regs);
     case OPTEE_SMC_CALL_WITH_ARG:
     case OPTEE_SMC_CALL_RETURN_FROM_RPC:
+        /* TODO: Add proper handling for this calls */
         forward_call(regs);
         return true;
     default:
-- 
2.7.4


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