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SubjectRe: [PATCH 02/14] arm64: Call ARCH_WORKAROUND_2 on transitions between EL0 and EL1
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On 24/05/18 12:23, Mark Rutland wrote:
> On Thu, May 24, 2018 at 12:00:58PM +0100, Mark Rutland wrote:
>> On Tue, May 22, 2018 at 04:06:36PM +0100, Marc Zyngier wrote:
>>> In order for the kernel to protect itself, let's call the SSBD mitigation
>>> implemented by the higher exception level (either hypervisor or firmware)
>>> on each transition between userspace and kernel.
>>>
>>> We must take the PSCI conduit into account in order to target the
>>> right exception level, hence the introduction of a runtime patching
>>> callback.
>>>
>>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>>> ---
>>> arch/arm64/kernel/cpu_errata.c | 18 ++++++++++++++++++
>>> arch/arm64/kernel/entry.S | 22 ++++++++++++++++++++++
>>> include/linux/arm-smccc.h | 5 +++++
>>> 3 files changed, 45 insertions(+)
>>>
>>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
>>> index a900befadfe8..46b3aafb631a 100644
>>> --- a/arch/arm64/kernel/cpu_errata.c
>>> +++ b/arch/arm64/kernel/cpu_errata.c
>>> @@ -232,6 +232,24 @@ enable_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
>>> }
>>> #endif /* CONFIG_HARDEN_BRANCH_PREDICTOR */
>>>
>>> +#ifdef CONFIG_ARM64_SSBD
>>> +void __init arm64_update_smccc_conduit(struct alt_instr *alt,
>>> + __le32 *origptr, __le32 *updptr,
>>> + int nr_inst)
>>> +{
>>> + u32 insn;
>>> +
>>> + BUG_ON(nr_inst != 1);
>>> +
>>> + if (psci_ops.conduit == PSCI_CONDUIT_HVC)
>>> + insn = aarch64_insn_get_hvc_value();
>>> + else
>>> + insn = aarch64_insn_get_smc_value();
>>
>> Shouldn't this also handle the case where there is no conduit?
>
> Due to the config symbol not being defined yet, and various other fixups
> in later patches, this is actually benign.
>
> However, if you make this:
>
> switch (psci_ops.conduit) {
> case PSCI_CONDUIT_NONE:
> return;
> case PSCI_CONDUIT_HVC:
> insn = aarch64_insn_get_hvc_value();
> break;
> case PSCI_CONDUIT_SMC:
> insn = aarch64_insn_get_smc_value();
> break;
> }
>
> ... then we won't even bother patching the nop in the default case
> regardless, which is nicer, IMO.

Yup, looks better to me too. I'll fold that in.

Thanks,

M.
--
Jazz is not dead. It just smells funny...

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