[U-Boot] [PATCH 1/6] ARM: add secure monitor handler to switch to non-secure state

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hi Andre,

On Mon,  6 May 2013 15:17:45 +0200, Andre Przywara
<andre.przywara@linaro.org> wrote:

> A prerequisite for using virtualization is to be in HYP mode, which
> requires the CPU to be in non-secure state.
> Introduce a monitor handler routine which switches the CPU to
> non-secure state by setting the NS and associated bits.
> According to the ARM ARM this should not be done in SVC mode, so we

ARM *TRM*, I suspect. Also, as there are a lot of ARM TRMs, if there is
a more precise reference, please provide it.

> have to setup a SMC handler for this. We reuse the current vector
> table for this and make sure that we only access the MVBAR register
> if the CPU supports the security extension and only if we
> configured the board to use it, since boards entering u-boot already
> in non-secure mode would crash on accessing MVBAR otherwise.
> 
> Signed-off-by: Andre Przywara <andre.przywara@linaro.org>
> ---
>  arch/arm/cpu/armv7/start.S | 31 ++++++++++++++++++++++++++++---
>  1 file changed, 28 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm/cpu/armv7/start.S b/arch/arm/cpu/armv7/start.S
> index e9e57e6..da48b36 100644
> --- a/arch/arm/cpu/armv7/start.S
> +++ b/arch/arm/cpu/armv7/start.S
> @@ -155,6 +155,13 @@ reset:
>  	/* Set vector address in CP15 VBAR register */
>  	ldr	r0, =_start
>  	mcr	p15, 0, r0, c12, c0, 0	@Set VBAR
> +
> +#ifdef CONFIG_ARMV7_VIRT
> +	mrc	p15, 0, r1, c0, c1, 1	@ check for security extension
> +	ands	r1, r1, #0x30
> +	mcrne	p15, 0, r0, c12, c0, 1	@ Set secure monitor MVBAR
> +#endif
> +
>  #endif
>  
>  	/* the mask ROM code should have PLL and others stable */
> @@ -257,6 +264,12 @@ ENTRY(c_runtime_cpu_setup)
>  	ldr     r0, =_start
>  	mcr     p15, 0, r0, c12, c0, 0  @Set VBAR
>  
> +#ifdef CONFIG_ARMV7_VIRT
> +	mrc	p15, 0, r1, c0, c1, 1	@ check for security extension
> +	ands	r1, r1, #0x30
> +	mcrne	p15, 0, r0, c12, c0, 1  @ Set secure monitor MVBAR
> +#endif
> +
>  	bx	lr
>  
>  ENDPROC(c_runtime_cpu_setup)
> @@ -490,11 +503,23 @@ undefined_instruction:
>  	bad_save_user_regs
>  	bl	do_undefined_instruction
>  
> +/*
> + * software interrupt aka. secure monitor handler
> + * This is executed on a "smc" instruction, we use a "smc #0" to switch
> + * to non-secure state
> + */
>  	.align	5
>  software_interrupt:
> -	get_bad_stack_swi
> -	bad_save_user_regs
> -	bl	do_software_interrupt
> +	mrc	p15, 0, r1, c1, c1, 0		@ read SCR
> +	bic	r1, r1, #0x07f
> +	orr	r1, r1, #0x31			@ enable NS, AW, FW
> +
> +	mrc	p15, 0, r0, c12, c0, 0		@ save secure copy of VBAR
> +	mcr	p15, 0, r1, c1, c1, 0		@ write SCR, switch to non-sec
> +	isb
> +	mcr	p15, 0, r0, c12, c0, 0		@ write non-secure copy of VBAR
> +
> +	movs	pc, lr
>  
>  	.align	5
>  prefetch_abort:


Amicalement,
-- 
Albert.