Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Message-ID: <8aa0cada-7f00-47b3-41e4-8a9e7beaae47@redhat.com>
Date:   Mon, 17 Jan 2022 18:45:36 +0100
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.4.0
Subject: Re: [PATCH 0/5] kvm: fix latent guest entry/exit bugs
Content-Language: en-US
To:     Mark Rutland <mark.rutland@arm.com>,
        Christian Borntraeger <borntraeger@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, aleksandar.qemu.devel@gmail.com,
        alexandru.elisei@arm.com, anup.patel@wdc.com,
        aou@eecs.berkeley.edu, atish.patra@wdc.com,
        benh@kernel.crashing.org, bp@alien8.de, catalin.marinas@arm.com,
        chenhuacai@kernel.org, dave.hansen@linux.intel.com,
        david@redhat.com, frankja@linux.ibm.com, frederic@kernel.org,
        gor@linux.ibm.com, hca@linux.ibm.com, imbrenda@linux.ibm.com,
        james.morse@arm.com, jmattson@google.com, joro@8bytes.org,
        kvm@vger.kernel.org, maz@kernel.org, mingo@redhat.com,
        mpe@ellerman.id.au, nsaenzju@redhat.com, palmer@dabbelt.com,
        paulmck@kernel.org, paulus@samba.org, paul.walmsley@sifive.com,
        seanjc@google.com, suzuki.poulose@arm.com, tglx@linutronix.de,
        tsbogend@alpha.franken.de, vkuznets@redhat.com,
        wanpengli@tencent.com, will@kernel.org
References: <20220111153539.2532246-1-mark.rutland@arm.com>
 <127a6117-85fb-7477-983c-daf09e91349d@linux.ibm.com>
 <YeFqUlhqY+7uzUT1@FVFF77S0Q05N>
 <ae1a42ab-f719-4a4e-8d2a-e2b4fa6e9580@linux.ibm.com>
 <YeF7Wvz05JhyCx0l@FVFF77S0Q05N>
 <b66c4856-7826-9cff-83f3-007d7ed5635c@linux.ibm.com>
 <YeGUnwhbSvwJz5pD@FVFF77S0Q05N>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <YeGUnwhbSvwJz5pD@FVFF77S0Q05N>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 1/14/22 16:19, Mark Rutland wrote:
> I also think there is another issue here. When an IRQ is taken from SIE, will
> user_mode(regs) always be false, or could it be true if the guest userspace is
> running? If it can be true I think tha context tracking checks can complain,
> and it*might*  be possible to trigger a panic().

I think that it would be false, because the guest PSW is in the SIE 
block and switched on SIE entry and exit, but I might be incorrect.

Paolo

> In irqentry_enter(), if user_mode(regs) == true, we call
> irqentry_enter_from_user_mode -> __enter_from_user_mode(). There we check that
> the context is CONTEXT_USER, but IIUC that will be CONTEXT_GUEST at this point.
> We also call arch_check_user_regs(), and IIUC this might permit a malicious
> guest to trigger a host panic by way of debug_user_asce(), but I may have
> misunderstood and that might not be possible.