Re: [PATCH v6 05/11] arm64: rsi: Map unprotected MMIO as decrypted

[Gavin Shan]

On 10/11/24 11:19 PM, Catalin Marinas wrote:
> On Tue, Oct 08, 2024 at 10:31:06AM +1000, Gavin Shan wrote:
> > On 10/5/24 12:43 AM, Steven Price wrote:
> > > diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
> > > index d7bba4cee627..f1add76f89ce 100644
> > > --- a/arch/arm64/kernel/rsi.c
> > > +++ b/arch/arm64/kernel/rsi.c
> > > @@ -6,6 +6,8 @@
> > >    #include <linux/jump_label.h>
> > >    #include <linux/memblock.h>
> > >    #include <linux/psci.h>
> > > +
> > > +#include <asm/io.h>
> > >    #include <asm/rsi.h>
> > >    struct realm_config config;
> > > @@ -92,6 +94,16 @@ bool arm64_is_protected_mmio(phys_addr_t base, size_t size)
> > >    }
> > >    EXPORT_SYMBOL(arm64_is_protected_mmio);
> > > +static int realm_ioremap_hook(phys_addr_t phys, size_t size, pgprot_t *prot)
> > > +{
> > > +	if (arm64_is_protected_mmio(phys, size))
> > > +		*prot = pgprot_encrypted(*prot);
> > > +	else
> > > +		*prot = pgprot_decrypted(*prot);
> > > +
> > > +	return 0;
> > > +}
> > > +
> >
> > We probably need arm64_is_mmio_private() here, meaning arm64_is_protected_mmio() isn't
> > sufficient to avoid invoking SMCCC call SMC_RSI_IPA_STATE_GET in a regular guest where
> > realm capability isn't present.
>
> I think we get away with this since the hook won't be registered in a
> normal guest (done from arm64_rsi_init()). So the additional check in
> arm64_is_mmio_private() is unnecessary.

Indeed. I missed the point that the hook won't be registered for a normal
guest. So we're good and safe.

Thanks,
Gavin