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

[Julien Grall <julien@xxxxxxx>]

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@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.
> 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