[PATCH 1/1] efi_selftest: check executing in EL2

[Ilias Apalodimas]

Hi Heinrich

On Fri, 11 Apr 2025 at 15:05, Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
> On 4/11/25 12:00, Ilias Apalodimas wrote:
> > Hi Heinrich,
> >
> > [...]
> >
> >> +
> >> +/**
> >> + * current_exception_level()
> >> + *
> >> + * Return:     current exception level, 0 - 3
> >> + */
> >> +static unsigned int current_exception_level(void)
> >> +{
> >> +       unsigned long el;
> >> +
> >> +       asm volatile (
> >> +               "MRS %0, CurrentEL"
> >> +               : "=r" (el) : : );
> >> +
> >> +       return (el >> 2) & 0x3;
> >> +}
> >> +
> >
> > We have an identical function in arch/arm/include/asm/system.h, can we
> > use that? It's static inline so you may be able to just include the
> > header file directly. Also, that function adds a 'cc,' which tells the
> > compiler that the instruction might change the condition code flags. I
> > don't remember if this is needed, but it doesn't hurt to have it.
>
> The function current_el() in arch/arm/include/asm/system.h is already
> used in switch_to_non_secure_mode() when determining if U-Boot should
> switch the exception state. Including the same function both in the code
> under test and in the test should be avoided.

Fair enough

>
> https://developer.arm.com/documentation/ddi0597/2025-03/Base-Instructions/MRS--Move-Special-register-to-general-purpose-register-
> does not describe any side effects when reading the CurrentEL flags?

Thanks for the link. It seems there isn't. It's only a read and should
not affect condition flags at all.

Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
>
> Best regards
>
> Heinrich
>
> >
> >
> >> +/**
> >> + * execute() - execute test
> >> + *
> >> + * Check that the exception level is not EL3.
> >> + */
> >> +static int execute(void)
> >> +{
> >> +       unsigned int el = current_exception_level();
> >> +
> >> +       efi_st_printf("Exception level EL%u\n", el);
> >> +       if (el != 1 && el != 2) {
> >> +               efi_st_error("EL1 or EL2 expected");
> >> +               return EFI_ST_FAILURE;
> >> +       }
> >> +
> >> +       return EFI_ST_SUCCESS;
> >> +}
> >> +
> >> +EFI_UNIT_TEST(el) = {
> >> +       .name = "exception level",
> >> +       .phase = EFI_EXECUTE_BEFORE_BOOTTIME_EXIT,
> >> +       .execute = execute,
> >> +};
> >> --
> >> 2.48.1
> >>
> >
> > Other than that LGTM
> >
> > /Ilias
>