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Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON
From: |
Alex Bennée |
Subject: |
Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32 |
Date: |
Wed, 09 Jan 2019 16:10:37 +0000 |
User-agent: |
mu4e 1.1.0; emacs 26.1.91 |
Alexander Graf <address@hidden> writes:
> In U-boot, we switch from S-SVC -> MON -> HYP when we want to enter
> HYP mode. This dance seems to work ok (hence it's there in the code
> base), but breaks with current QEMU.
What EL is MON in this case? EL3? In which case I'm confused by the
terminology as the ARM ARM states:
The principles of the ARMv8-A security model are:
• If the implementation includes EL3, then it has two Security states, Secure
and Non-secure, and:
— EL3 exists only in Secure state.
— A change from Non-secure state to Secure state can only occur on taking
an exception to EL3.
— A change from Secure state to Non-secure state can only occur on an
exception return from EL3.
We don't currently implement ARMv8.4-SecEL2 but that adds secure EL2 but
as you can only switch security state in in/out of EL3 you have to be go
to the secure monitor before you enter it.
> The reason seems to be that we try to see whether we are entering
> HYP mode from the NS side. However, MON is always considered secure,
> so we always fall into an error case when going MON->HYP and never
> manage to actually do the switch.
>
> Fix this by not using a different helper function that does not bork
> when we're in MON state, as that switch is supposed to work.
>
> Signed-off-by: Alexander Graf <address@hidden>
> ---
> target/arm/helper.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/arm/helper.c b/target/arm/helper.c
> index f00c141ef9..9bf8fbd8f9 100644
> --- a/target/arm/helper.c
> +++ b/target/arm/helper.c
> @@ -6297,7 +6297,7 @@ static int bad_mode_switch(CPUARMState *env, int mode,
> CPSRWriteType write_type)
> return 0;
> case ARM_CPU_MODE_HYP:
> return !arm_feature(env, ARM_FEATURE_EL2)
> - || arm_current_el(env) < 2 || arm_is_secure(env);
> + || arm_current_el(env) < 2 ||
> arm_is_secure_below_el3(env);
This seems to violate the rule that you can enter a NS state from
anything other than EL3.
> case ARM_CPU_MODE_MON:
> return arm_current_el(env) < 3;
> default:
--
Alex Bennée
- [Qemu-arm] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32, Alexander Graf, 2019/01/09
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32,
Alex Bennée <=
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32, Peter Maydell, 2019/01/09
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32, Peter Maydell, 2019/01/09
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32, Alexander Graf, 2019/01/09
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32, Peter Maydell, 2019/01/09
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32, Alexander Graf, 2019/01/10
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32, Peter Maydell, 2019/01/10
- Re: [Qemu-arm] [Qemu-devel] [PATCH] target/arm: Allow to switch from MON->HYP on AArch32, Peter Maydell, 2019/01/17