From: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
To: Julien Grall <julien.grall@arm.com>
Cc: "tee-dev@lists.linaro.org" <tee-dev@lists.linaro.org>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Stefano Stabellini <sstabellini@kernel.org>,
Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [PATCH 4/5] xen/arm: optee: handle share buffer translation error
Date: Wed, 11 Sep 2019 18:32:28 +0000 [thread overview]
Message-ID: <87mufafzus.fsf@epam.com> (raw)
In-Reply-To: <53631114-2bb1-18a8-615d-3768facdcc78@arm.com>
Julien Grall writes:
> 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@epam.com>
>> ---
>> 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?
Yep. This is a bad habit. Will remove.
>
>> + 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?
Because I'm bad at naming things :)
OPTEEM_CALL_STATE_XEN_RPC looks too long. But you are right, so I'll
rename the enum values. Unless, you have a better idea for this.
>
>> +};
>> +
>> 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?
Yes, right. Will rename.
>> + 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"?
There will be memory leak somewhere in the guest. Yes, looks
like it is misleading...
What I mean, is that OP-TEE requests guest to allocate some
memory. Guest does not know, when OP-TEE finishes using this memory, so
guest will free the memory only by OP-TEE's request. We can't emulate
this request in current circumstances, so guest will keep part of own
memory reserved for OP-TEE infinitely.
> What the state of the page from Xen PoV?
From Xen point of view all will be perfectly fine.
> I.e. is there any reference
> taken by the OP-TEE mediator? Will the page be freed once the guest is
> destroyed?...
As I said, it has nothing to do with the page as Xen it sees. Mediator
will call put_page() prior to entering this function. So, no Xen
resources are used.
>
>> + */
>> + 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?
It is strange, that it is missing, actually. Looks like I forgot to add
it. But, looking at xen-error-handling, maybe BOG_ON() would be better?
>> +
>> + /*
>> + * We are not checking return value from a guest because we assume
>> + * that OPTEE_RPC_CMD_SHM_FREE newer fails.
>
> s/newer/never/
Oops. Thank you.
>> + */
>> +
>> + 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"?
Yes, I do.
> Also s/error/an error/
Sure. Thank you.
--
Volodymyr Babchuk at EPAM
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next prev parent reply other threads:[~2019-09-11 18:33 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-23 18:48 [Xen-devel] [PATCH 0/5] arch/arm: optee: fix TODOs and remove "experimental" status Volodymyr Babchuk
2019-08-23 18:48 ` [Xen-devel] [PATCH 1/5] xen/arm: optee: impose limit on shared buffer size Volodymyr Babchuk
2019-09-09 22:11 ` Julien Grall
2019-09-11 18:48 ` Volodymyr Babchuk
2019-09-12 19:32 ` Julien Grall
2019-09-12 19:45 ` Volodymyr Babchuk
2019-09-12 19:51 ` Julien Grall
2019-09-16 15:26 ` Volodymyr Babchuk
2019-09-17 10:49 ` Julien Grall
2019-09-17 12:28 ` Volodymyr Babchuk
2019-09-17 18:46 ` Julien Grall
2019-08-23 18:48 ` [Xen-devel] [PATCH 2/5] xen/arm: optee: check for preemption while freeing shared buffers Volodymyr Babchuk
2019-09-09 22:19 ` Julien Grall
2019-09-11 18:53 ` Volodymyr Babchuk
2019-09-12 19:39 ` Julien Grall
2019-09-12 19:47 ` Volodymyr Babchuk
2019-08-23 18:48 ` [Xen-devel] [PATCH 3/5] xen/arm: optee: limit number of " Volodymyr Babchuk
2019-08-23 18:48 ` [Xen-devel] [PATCH 4/5] xen/arm: optee: handle share buffer translation error Volodymyr Babchuk
2019-09-10 11:17 ` Julien Grall
2019-09-11 18:32 ` Volodymyr Babchuk [this message]
2019-09-12 18:55 ` Julien Grall
2019-08-23 18:48 ` [Xen-devel] [PATCH 5/5] xen/arm: optee: remove experimental status Volodymyr Babchuk
2019-08-23 19:05 ` Julien Grall
2019-08-23 19:20 ` Volodymyr Babchuk
2019-09-09 21:31 ` Julien Grall
2019-09-11 18:41 ` Volodymyr Babchuk
2019-09-12 19:00 ` Julien Grall
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