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From: Marc Zyngier <maz@kernel.org>
To: James Morse <james.morse@arm.com>
Cc: linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
	Julien Thierry <julien.thierry.kdev@gmail.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Andrew Scull <ascull@google.com>, Will Deacon <will@kernel.org>,
	Quentin Perret <qperret@google.com>,
	David Brazdil <dbrazdil@google.com>,
	kernel-team@android.com
Subject: Re: [PATCH 04/11] KVM: arm64: Move PC rollback on SError to HYP
Date: Tue, 27 Oct 2020 14:59:14 +0000	[thread overview]
Message-ID: <cd5527f7308f1db09268efd7c83e51c5@kernel.org> (raw)
In-Reply-To: <e2487f06-3f2f-1a0b-49d8-a72ea9288bb2@arm.com>

On 2020-10-27 14:56, James Morse wrote:
> Hi Marc,
> 
> On 26/10/2020 13:34, Marc Zyngier wrote:
>> Instead of handling the "PC rollback on SError during HVC" at EL1 
>> (which
>> requires disclosing PC to a potentially untrusted kernel), let's move
>> this fixup to ... fixup_guest_exit(), which is where we do all fixups.
> 
>> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h 
>> b/arch/arm64/kvm/hyp/include/hyp/switch.h
>> index d687e574cde5..668f02c7b0b3 100644
>> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
>> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
>> @@ -411,6 +411,21 @@ static inline bool fixup_guest_exit(struct 
>> kvm_vcpu *vcpu, u64 *exit_code)
>>  	if (ARM_EXCEPTION_CODE(*exit_code) != ARM_EXCEPTION_IRQ)
>>  		vcpu->arch.fault.esr_el2 = read_sysreg_el2(SYS_ESR);
>> 
>> +	if (ARM_SERROR_PENDING(*exit_code)) {
>> +		u8 esr_ec = kvm_vcpu_trap_get_class(vcpu);
>> +
>> +		/*
>> +		 * HVC already have an adjusted PC, which we need to
>> +		 * correct in order to return to after having injected
>> +		 * the SError.
>> +		 *
>> +		 * SMC, on the other hand, is *trapped*, meaning its
>> +		 * preferred return address is the SMC itself.
>> +		 */
>> +		if (esr_ec == ESR_ELx_EC_HVC32 || esr_ec == ESR_ELx_EC_HVC64)
>> +			*vcpu_pc(vcpu) -= 4;
> 
> Isn't *vcpu_pc(vcpu) the PC of the previous entry for this vcpu?....
> its not the PC of the
> exit until __sysreg_save_el2_return_state() saves it, which happens 
> just after
> fixup_guest_exit().

Hmmm. Good point. The move was obviously done in haste, thank you for 
pointing
this blatant bug.

> Mess with ELR_EL2 directly?

Yes, that's the best course of action. We never run this code anyway.

Thanks,

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

  reply	other threads:[~2020-10-27 17:13 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-26 13:34 [PATCH 00/11] KVM: arm64: Move PC/ELR/SPSR/PSTATE updatess to EL2 Marc Zyngier
2020-10-26 13:34 ` [PATCH 01/11] KVM: arm64: Don't adjust PC on SError during SMC trap Marc Zyngier
2020-10-26 13:53   ` Mark Rutland
2020-10-26 14:08     ` Marc Zyngier
2020-10-26 14:22       ` Mark Rutland
2020-10-26 13:34 ` [PATCH 02/11] KVM: arm64: Move kvm_vcpu_trap_il_is32bit into kvm_skip_instr32() Marc Zyngier
2020-10-26 13:55   ` Mark Rutland
2020-10-26 13:34 ` [PATCH 03/11] KVM: arm64: Make kvm_skip_instr() and co private to HYP Marc Zyngier
2020-10-26 14:04   ` Mark Rutland
2020-10-27 16:17     ` Marc Zyngier
2020-10-27 10:55   ` Suzuki K Poulose
2020-10-27 11:08     ` Marc Zyngier
2020-10-26 13:34 ` [PATCH 04/11] KVM: arm64: Move PC rollback on SError " Marc Zyngier
2020-10-26 14:06   ` Mark Rutland
2020-10-27 14:56   ` James Morse
2020-10-27 14:59     ` Marc Zyngier [this message]
2020-10-26 13:34 ` [PATCH 05/11] KVM: arm64: Move VHE direct sysreg accessors into kvm_host.h Marc Zyngier
2020-10-26 14:07   ` Mark Rutland
2020-10-26 13:34 ` [PATCH 06/11] KVM: arm64: Add basic hooks for injecting exceptions from EL2 Marc Zyngier
2020-10-26 13:34 ` [PATCH 07/11] KVM: arm64: Inject AArch64 exceptions from HYP Marc Zyngier
2020-10-26 14:22   ` Mark Rutland
2020-10-27 16:21     ` Marc Zyngier
2020-10-27 17:41   ` James Morse
2020-10-27 18:49     ` Marc Zyngier
2020-10-26 13:34 ` [PATCH 08/11] KVM: arm64: Inject AArch32 " Marc Zyngier
2020-10-26 14:26   ` Mark Rutland
2020-10-27 17:41   ` James Morse
2020-10-27 19:21     ` Marc Zyngier
2020-10-28 19:20       ` James Morse
2020-10-28 20:24         ` Marc Zyngier
2020-10-26 13:34 ` [PATCH 09/11] KVM: arm64: Remove SPSR manipulation primitives Marc Zyngier
2020-10-26 14:30   ` Mark Rutland
2020-10-26 13:34 ` [PATCH 10/11] KVM: arm64: Consolidate exception injection Marc Zyngier
2020-10-26 13:34 ` [PATCH 11/11] KVM: arm64: Get rid of the AArch32 register mapping code Marc Zyngier

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