[PATCH v1] arm/optee: Use only least 32 bits for SMC type arg according to SMCCC

[PATCH v1] arm/optee: Use only least 32 bits for SMC type arg according to SMCCC

[Roman Skakun]

This patch added additional sanity and increases an understanding for
getting proper value from the first argument for SMC call on aarch64
according to SMCC Convention.

[0] ARM DEN0028B, page 12

Signed-off-by: Roman Skakun <roman_skakun@epam.com>
---
 xen/arch/arm/tee/optee.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
index ee85359742..87060b52b8 100644
--- a/xen/arch/arm/tee/optee.c
+++ b/xen/arch/arm/tee/optee.c
@@ -1643,7 +1643,8 @@ static bool optee_handle_call(struct cpu_user_regs *regs)
     if ( !ctx )
         return false;
 
-    switch ( get_user_reg(regs, 0) )
+    /* Only least 32 bits are significant (see ARM DEN 0028B, page 12) */
+    switch ( (uint32_t)get_user_reg(regs, 0) )
     {
     case OPTEE_SMC_CALLS_COUNT:
         set_user_reg(regs, 0, OPTEE_MEDIATOR_SMC_COUNT);
-- 
2.25.1

Re: [PATCH v1] arm/optee: Use only least 32 bits for SMC type arg according to SMCCC

[Volodymyr Babchuk]

Hi Roman,

Thank you for the contribution.

Roman Skakun writes:

> This patch added additional sanity and increases an understanding for
> getting proper value from the first argument for SMC call on aarch64
> according to SMCC Convention.
>
> [0] ARM DEN0028B, page 12
>
> Signed-off-by: Roman Skakun <roman_skakun@epam.com>

Acked-by: Volodymyr Babchyk <volodymyr_babchuk@epam.com>

> ---
>  xen/arch/arm/tee/optee.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
> index ee85359742..87060b52b8 100644
> --- a/xen/arch/arm/tee/optee.c
> +++ b/xen/arch/arm/tee/optee.c
> @@ -1643,7 +1643,8 @@ static bool optee_handle_call(struct cpu_user_regs *regs)
>      if ( !ctx )
>          return false;
>  
> -    switch ( get_user_reg(regs, 0) )
> +    /* Only least 32 bits are significant (see ARM DEN 0028B, page 12) */
> +    switch ( (uint32_t)get_user_reg(regs, 0) )
>      {
>      case OPTEE_SMC_CALLS_COUNT:
>          set_user_reg(regs, 0, OPTEE_MEDIATOR_SMC_COUNT);


-- 
Volodymyr Babchuk at EPAM

Re: [PATCH v1] arm/optee: Use only least 32 bits for SMC type arg according to SMCCC

[Julien Grall]

Hi Roman,

On 06/01/2021 11:26, Roman Skakun wrote:
> This patch added additional sanity and increases an understanding for
> getting proper value from the first argument for SMC call on aarch64
> according to SMCC Convention.

I would suggest the following commit message:

"xen/arm: optee: The function identifier is always 32-bit

Per the SMCCC specification (see section 3.1 in ARM DEN 0028D), the 
function identifier is only stored in the least significant 32-bits. The 
most significant 32-bits should be ignored.

The function optee_handle_call() is now updated to ignore the most 
significant 32-bits.

"

Note that I used the version D rather than B because the latter has 
buggy wording (it seems to suggest that the least significants bits 
should be ignored).

Furthermore, I checked vsmc.c (the layer that dispatch the SMC) and it 
was already handled properly thanks to commit 7f4217cc6057 "xen/arm: 
vsmc: The function identifier is always 32-bit".

> [0] ARM DEN0028B, page 12
> 
> Signed-off-by: Roman Skakun <roman_skakun@epam.com>
> ---
>   xen/arch/arm/tee/optee.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
> index ee85359742..87060b52b8 100644
> --- a/xen/arch/arm/tee/optee.c
> +++ b/xen/arch/arm/tee/optee.c
> @@ -1643,7 +1643,8 @@ static bool optee_handle_call(struct cpu_user_regs *regs)
>       if ( !ctx )
>           return false;
>   
> -    switch ( get_user_reg(regs, 0) )
> +    /* Only least 32 bits are significant (see ARM DEN 0028B, page 12) */

I would suggest:

/* The function identifier is always stored in the least significant 
32-bit (see section ARM DEN 0028D) */

I can update it while committing, if both Volodymyr and you are happy 
with changes.

Cheers,

> +    switch ( (uint32_t)get_user_reg(regs, 0) )
>       {
>       case OPTEE_SMC_CALLS_COUNT:
>           set_user_reg(regs, 0, OPTEE_MEDIATOR_SMC_COUNT);
> 

-- 
Julien Grall

Re: [PATCH v1] arm/optee: Use only least 32 bits for SMC type arg according to SMCCC

[Volodymyr Babchuk]

Hi Julien,

Julien Grall writes:

> Hi Roman,
>
> On 06/01/2021 11:26, Roman Skakun wrote:
>> This patch added additional sanity and increases an understanding for
>> getting proper value from the first argument for SMC call on aarch64
>> according to SMCC Convention.
>
> I would suggest the following commit message:
>
> "xen/arm: optee: The function identifier is always 32-bit
>
> Per the SMCCC specification (see section 3.1 in ARM DEN 0028D), the
> function identifier is only stored in the least significant
> 32-bits. The most significant 32-bits should be ignored.
>
> The function optee_handle_call() is now updated to ignore the most
> significant 32-bits.
>
> "
>
> Note that I used the version D rather than B because the latter has
> buggy wording (it seems to suggest that the least significants bits 
> should be ignored).
>
> Furthermore, I checked vsmc.c (the layer that dispatch the SMC) and it
> was already handled properly thanks to commit 7f4217cc6057 "xen/arm: 
> vsmc: The function identifier is always 32-bit".
>
>> [0] ARM DEN0028B, page 12
>> Signed-off-by: Roman Skakun <roman_skakun@epam.com>
>> ---
>>   xen/arch/arm/tee/optee.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>> diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
>> index ee85359742..87060b52b8 100644
>> --- a/xen/arch/arm/tee/optee.c
>> +++ b/xen/arch/arm/tee/optee.c
>> @@ -1643,7 +1643,8 @@ static bool optee_handle_call(struct cpu_user_regs *regs)
>>       if ( !ctx )
>>           return false;
>>   -    switch ( get_user_reg(regs, 0) )
>> +    /* Only least 32 bits are significant (see ARM DEN 0028B, page 12) */
>
> I would suggest:
>
> /* The function identifier is always stored in the least significant
> 32-bit (see section ARM DEN 0028D) */
>
> I can update it while committing, if both Volodymyr and you are happy
> with changes.

I'm totally fine with the proposed changes. Thank you for tidying this up.

-- 
Volodymyr Babchuk at EPAM

Re: [PATCH v1] arm/optee: Use only least 32 bits for SMC type arg according to SMCCC

[Julien Grall]

On 06/01/2021 23:22, Volodymyr Babchuk wrote:
> 
> Hi Julien,
> 
> Julien Grall writes:
> 
>> Hi Roman,
>>
>> On 06/01/2021 11:26, Roman Skakun wrote:
>>> This patch added additional sanity and increases an understanding for
>>> getting proper value from the first argument for SMC call on aarch64
>>> according to SMCC Convention.
>>
>> I would suggest the following commit message:
>>
>> "xen/arm: optee: The function identifier is always 32-bit
>>
>> Per the SMCCC specification (see section 3.1 in ARM DEN 0028D), the
>> function identifier is only stored in the least significant
>> 32-bits. The most significant 32-bits should be ignored.
>>
>> The function optee_handle_call() is now updated to ignore the most
>> significant 32-bits.
>>
>> "
>>
>> Note that I used the version D rather than B because the latter has
>> buggy wording (it seems to suggest that the least significants bits
>> should be ignored).
>>
>> Furthermore, I checked vsmc.c (the layer that dispatch the SMC) and it
>> was already handled properly thanks to commit 7f4217cc6057 "xen/arm:
>> vsmc: The function identifier is always 32-bit".
>>
>>> [0] ARM DEN0028B, page 12
>>> Signed-off-by: Roman Skakun <roman_skakun@epam.com>
>>> ---
>>>    xen/arch/arm/tee/optee.c | 3 ++-
>>>    1 file changed, 2 insertions(+), 1 deletion(-)
>>> diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
>>> index ee85359742..87060b52b8 100644
>>> --- a/xen/arch/arm/tee/optee.c
>>> +++ b/xen/arch/arm/tee/optee.c
>>> @@ -1643,7 +1643,8 @@ static bool optee_handle_call(struct cpu_user_regs *regs)
>>>        if ( !ctx )
>>>            return false;
>>>    -    switch ( get_user_reg(regs, 0) )
>>> +    /* Only least 32 bits are significant (see ARM DEN 0028B, page 12) */
>>
>> I would suggest:
>>
>> /* The function identifier is always stored in the least significant
>> 32-bit (see section ARM DEN 0028D) */
>>
>> I can update it while committing, if both Volodymyr and you are happy
>> with changes.
> 
> I'm totally fine with the proposed changes. Thank you for tidying this up.

Thanks! I have updated the patch and committed it.

Cheers,

> 

-- 
Julien Grall