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Re: [Xen-devel] [PATCH 4/5] xen/arm: optee: handle share buffer translation error
Hi Volodymyr,
On 8/23/19 7:48 PM, Volodymyr Babchuk wrote:
There is a case possible, when OP-TEE asks guest to allocate shared
buffer, but Xen for some reason can't translate buffer's addresses. In
this situation we should do two things:
1. Tell guest to free allocated buffer, so there will be no memory
leak for guest.
2. Tell OP-TEE that buffer allocation failed.
To ask guest to free allocated buffer we should perform the same
thing, as OP-TEE does - issue RPC request. This is done by filling
request buffer (luckily we can reuse the same buffer, that OP-TEE used
to issue original request) and then return to guest with special
return code.
Then we need to handle next call from guest in a special way: as RPC
was issued by Xen, not by OP-TEE, it should be handled by Xen.
Basically, this is the mechanism to preempt OP-TEE mediator.
The same mechanism can be used in the future to preempt mediator
during translation large (>512 pages) shared buffers.
Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
---
xen/arch/arm/tee/optee.c | 167 +++++++++++++++++++++++++++++++--------
1 file changed, 136 insertions(+), 31 deletions(-)
diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
index 3ce6e7fa55..4eebc60b62 100644
--- a/xen/arch/arm/tee/optee.c
+++ b/xen/arch/arm/tee/optee.c
@@ -96,6 +96,11 @@
OPTEE_SMC_SEC_CAP_UNREGISTERED_SHM | \
OPTEE_SMC_SEC_CAP_DYNAMIC_SHM)
+enum optee_call_state {
+ OPTEEM_CALL_NORMAL = 0,
enum always start counting at 0. Also, looking at the code, it does not
seem you need to know the value. Right?
+ OPTEEM_CALL_XEN_RPC,
I am a bit confused, the enum is called optee_call_state but all the
enum are prefixed with OPTEEM_CALL_. Why the discrepancy?
+};
+
static unsigned int __read_mostly max_optee_threads;
/*
@@ -112,6 +117,9 @@ struct optee_std_call {
paddr_t guest_arg_ipa;
int optee_thread_id;
int rpc_op;
+ /* Saved buffer type for the last buffer allocate request */
Looking at the code, it feels to me you are saving the buffer type for
the current command and not the last. Did I miss anything?
+ unsigned int rpc_buffer_type;
+ enum optee_call_state state;
uint64_t rpc_data_cookie;
bool in_flight;
register_t rpc_params[2];
@@ -299,6 +307,7 @@ static struct optee_std_call *allocate_std_call(struct
optee_domain *ctx)
call->optee_thread_id = -1;
call->in_flight = true;
+ call->state = OPTEEM_CALL_NORMAL;
spin_lock(&ctx->lock);
list_add_tail(&call->list, &ctx->call_list);
@@ -1075,6 +1084,10 @@ static int handle_rpc_return(struct optee_domain *ctx,
ret = -ERESTART;
}
+ /* Save the buffer type in case we will want to free it */
+ if ( shm_rpc->xen_arg->cmd == OPTEE_RPC_CMD_SHM_ALLOC )
+ call->rpc_buffer_type = shm_rpc->xen_arg->params[0].u.value.a;
+
unmap_domain_page(shm_rpc->xen_arg);
}
@@ -1239,18 +1252,102 @@ err:
return;
}
+/*
+ * Prepare RPC request to free shared buffer in the same way, as
+ * OP-TEE does this.
+ *
+ * Return values:
+ * true - successfully prepared RPC request
+ * false - there was an error
+ */
+static bool issue_rpc_cmd_free(struct optee_domain *ctx,
+ struct cpu_user_regs *regs,
+ struct optee_std_call *call,
+ struct shm_rpc *shm_rpc,
+ uint64_t cookie)
+{
+ register_t r1, r2;
+
+ /* In case if guest will forget to update it with meaningful value */
+ shm_rpc->xen_arg->ret = TEEC_ERROR_GENERIC;
+ shm_rpc->xen_arg->cmd = OPTEE_RPC_CMD_SHM_FREE;
+ shm_rpc->xen_arg->num_params = 1;
+ shm_rpc->xen_arg->params[0].attr = OPTEE_MSG_ATTR_TYPE_VALUE_INPUT;
+ shm_rpc->xen_arg->params[0].u.value.a = call->rpc_buffer_type;
+ shm_rpc->xen_arg->params[0].u.value.b = cookie;
+
+ if ( access_guest_memory_by_ipa(current->domain,
+ gfn_to_gaddr(shm_rpc->gfn),
+ shm_rpc->xen_arg,
+ OPTEE_MSG_GET_ARG_SIZE(1),
+ true) )
+ {
+ /*
+ * Well, this is quite bad. We have error in error path.
+ * This can happen only if guest behaves badly, so all
+ * we can do is to return error to OP-TEE and leave
+ * guest's memory leaked.
Could you expand a bit more what you mean by "guest's memory leaked"?
What the state of the page from Xen PoV? I.e. is there any reference
taken by the OP-TEE mediator? Will the page be freed once the guest is
destroyed?...
+ */
+ shm_rpc->xen_arg->ret = TEEC_ERROR_GENERIC;
+ shm_rpc->xen_arg->num_params = 0;
+
+ return false;
+ }
+
+ uint64_to_regpair(&r1, &r2, shm_rpc->cookie);
+
+ call->state = OPTEEM_CALL_XEN_RPC;
+ call->rpc_op = OPTEE_SMC_RPC_FUNC_CMD;
+ call->rpc_params[0] = r1;
+ call->rpc_params[1] = r2;
+ call->optee_thread_id = get_user_reg(regs, 3);
+
+ set_user_reg(regs, 0, OPTEE_SMC_RETURN_RPC_CMD);
+ set_user_reg(regs, 1, r1);
+ set_user_reg(regs, 2, r2);
+
+ return true;
+}
+
+/* Handles return from Xen-issued RPC */
+static void handle_xen_rpc_return(struct optee_domain *ctx,
+ struct cpu_user_regs *regs,
+ struct optee_std_call *call,
+ struct shm_rpc *shm_rpc)
+{
+ call->state = OPTEEM_CALL_NORMAL;
+
+ /*
+ * Right now we have only one reason to be there - we asked guest
+ * to free shared buffer and it did it. Now we can tell OP-TEE that
+ * buffer allocation failed.
+ */
Should we add an ASSERT to ensure the command is the one we expect?
+
+ /*
+ * We are not checking return value from a guest because we assume
+ * that OPTEE_RPC_CMD_SHM_FREE newer fails.
s/newer/never/
+ */
+
+ shm_rpc->xen_arg->ret = TEEC_ERROR_GENERIC;
+ shm_rpc->xen_arg->num_params = 0;
+}
+
/*
* This function is called when guest is finished processing RPC
* request from OP-TEE and wished to resume the interrupted standard
* call.
+ *
+ * Return values:
+ * false - there was an error, do not call OP-TEE
+ * true - success, proceed as normal
*/
-static void handle_rpc_cmd_alloc(struct optee_domain *ctx,
+static bool handle_rpc_cmd_alloc(struct optee_domain *ctx,
struct cpu_user_regs *regs,
struct optee_std_call *call,
struct shm_rpc *shm_rpc)
{
if ( shm_rpc->xen_arg->ret || shm_rpc->xen_arg->num_params != 1 )
- return;
+ return true;
if ( shm_rpc->xen_arg->params[0].attr != (OPTEE_MSG_ATTR_TYPE_TMEM_OUTPUT |
OPTEE_MSG_ATTR_NONCONTIG) )
@@ -1258,7 +1355,7 @@ static void handle_rpc_cmd_alloc(struct optee_domain *ctx,
gdprintk(XENLOG_WARNING,
"Invalid attrs for shared mem buffer: %"PRIx64"\n",
shm_rpc->xen_arg->params[0].attr);
- return;
+ return true;
}
/* Free pg list for buffer */
@@ -1274,21 +1371,14 @@ static void handle_rpc_cmd_alloc(struct optee_domain
*ctx,
{
call->rpc_data_cookie = 0;
/*
- * Okay, so there was problem with guest's buffer and we need
- * to tell about this to OP-TEE.
- */
- shm_rpc->xen_arg->ret = TEEC_ERROR_GENERIC;
- shm_rpc->xen_arg->num_params = 0;
- /*
- * TODO: With current implementation, OP-TEE will not issue
- * RPC to free this buffer. Guest and OP-TEE will be out of
- * sync: guest believes that it provided buffer to OP-TEE,
- * while OP-TEE thinks of opposite. Ideally, we need to
- * emulate RPC with OPTEE_MSG_RPC_CMD_SHM_FREE command.
+ * We are unable to translate guest's buffer, so we need tell guest
+ * to free it, before returning error to OP-TEE.
Do you mean "reporting" instead of "returning"?
Also s/error/an error/
*/
- gprintk(XENLOG_WARNING,
- "translate_noncontig() failed, OP-TEE/guest state is out of
sync.\n");
+ return !issue_rpc_cmd_free(ctx, regs, call, shm_rpc,
+ shm_rpc->xen_arg->params[0].u.tmem.shm_ref);
}
+
+ return true;
}
static void handle_rpc_cmd(struct optee_domain *ctx, struct cpu_user_regs *regs,
@@ -1338,22 +1428,37 @@ static void handle_rpc_cmd(struct optee_domain *ctx,
struct cpu_user_regs *regs,
goto out;
}
- switch (shm_rpc->xen_arg->cmd)
+ if ( call->state == OPTEEM_CALL_NORMAL )
{
- case OPTEE_RPC_CMD_GET_TIME:
- case OPTEE_RPC_CMD_WAIT_QUEUE:
- case OPTEE_RPC_CMD_SUSPEND:
- break;
- case OPTEE_RPC_CMD_SHM_ALLOC:
- handle_rpc_cmd_alloc(ctx, regs, call, shm_rpc);
- break;
- case OPTEE_RPC_CMD_SHM_FREE:
- free_optee_shm_buf(ctx, shm_rpc->xen_arg->params[0].u.value.b);
- if ( call->rpc_data_cookie == shm_rpc->xen_arg->params[0].u.value.b )
- call->rpc_data_cookie = 0;
- break;
- default:
- break;
+ switch (shm_rpc->xen_arg->cmd)
+ {
+ case OPTEE_RPC_CMD_GET_TIME:
+ case OPTEE_RPC_CMD_WAIT_QUEUE:
+ case OPTEE_RPC_CMD_SUSPEND:
+ break;
+ case OPTEE_RPC_CMD_SHM_ALLOC:
+ if ( !handle_rpc_cmd_alloc(ctx, regs, call, shm_rpc) )
+ {
+ /* We failed to translate buffer, report back to guest */
+ unmap_domain_page(shm_rpc->xen_arg);
+ put_std_call(ctx, call);
+
+ return;
+ }
+ break;
+ case OPTEE_RPC_CMD_SHM_FREE:
+ free_optee_shm_buf(ctx, shm_rpc->xen_arg->params[0].u.value.b);
+ if ( call->rpc_data_cookie ==
+ shm_rpc->xen_arg->params[0].u.value.b )
+ call->rpc_data_cookie = 0;
+ break;
+ default:
+ break;
+ }
+ }
+ else
+ {
+ handle_xen_rpc_return(ctx, regs, call, shm_rpc);
}
out:
Cheers,
--
Julien Grall
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