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

[Julien Grall <julien@xxxxxxx>]

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@xxxxxxxx>
> ---
>   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