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[104.199.15.117]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e538a547bsm139388055e9.5.2026.05.07.07.13.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 May 2026 07:13:10 -0700 (PDT) Date: Thu, 7 May 2026 14:13:06 +0000 From: Sebastian Ene To: Marc Zyngier Cc: catalin.marinas@arm.com, oupton@kernel.org, will@kernel.org, joey.gouly@arm.com, korneld@google.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, android-kvm@google.com, mrigendra.chaubey@gmail.com, perlarsen@google.com, suzuki.poulose@arm.com, vdonnefort@google.com, yuzenghui@huawei.com, Sudeep Holla Subject: Re: [PATCH] KVM: arm64: Forward FFA_NOTIFICATION* calls to TrustZone Message-ID: References: <20260501114447.2389222-2-sebastianene@google.com> <86wlxgy00t.wl-maz@kernel.org> <86se83xrwx.wl-maz@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <86se83xrwx.wl-maz@kernel.org> On Thu, May 07, 2026 at 02:36:46PM +0100, Marc Zyngier wrote: > On Thu, 07 May 2026 11:48:46 +0100, > Sebastian Ene wrote: > > > > On Wed, May 06, 2026 at 05:29:22PM +0100, Marc Zyngier wrote: > > > > Hello Marc, > > > > > [+ Sudeep] > > > > > > On Fri, 01 May 2026 12:44:48 +0100, > > > Sebastian Ene wrote: > > > > > > > > Remove the FFA_NOTIFICATION* calls from the blocklist used by the pKVM > > > > FF-A proxy. This restriction was preventing the use of asynchronous > > > > signaling mechanisms defined by the Arm FF-A specification to > > > > communicate with the secure services. > > > > While these calls are markes as optional, there is no reason why the > > > > hypervisor proxy would block them because: > > > > > > > > 1. Host is the Sole Non-Secure Endpoint: The Host operates as the > > > > only Non-Secure VM ID (VM ID 0) recognized by the Secure World. > > > > > > Where is this enforced? > > > > > > > There is no enforcement in place in the hypervisor since we don't proxy > > FF-A from guest VMs, there is only one non-secure user of this which is the host. > > And again: what makes that VM ID 0? Why can't the host pick VM ID 32 > and use that? > The host discovers its id through the FFA_ID_GET and TZ returns 0 in this case. However if it wants to use VM ID 32 in any other call it absolutely can but what would it be the attack here, what is your concern ? > > > > Because all forwarded notifications are inherently attributed to > > > > the Host by the SPMC, there is no risk of VM ID spoofing > > > > originating from the Normal World. > > > > > > I don't understand: either the host is always using VM ID 0, and we > > > have ways to check and enforce this (how?), or the simple fact that > > > the request comes from NS is a guarantee that the SPMC will treat the > > > VM ID as 0. > > > > > > Which one is it? > > > > My understanding is that when the hypervisor doesn't handle the allocation of > > the non-secure IDs (through FFA_ID_GET), everything that comes from non-secure > > is treated as having the VM ID 0 by the SPMC. > > This looks terribly fragile. I'd rather you *enforce* these things > rather than allowing any random stuff from the host and relying on > the EL3 firmware to get it right (odds are that it won't). > I can verify the vmid is 0 for the notification calls that I enable. > This also ties into this: > > > > > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c > > > > index 1af722771178..a82d0cd22a17 100644 > > > > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c > > > > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c > > > > @@ -675,14 +675,6 @@ static bool ffa_call_supported(u64 func_id) > > > > case FFA_RXTX_MAP: > > > > case FFA_MEM_DONATE: > > > > case FFA_MEM_RETRIEVE_REQ: > > > > - /* Optional notification interfaces added in FF-A 1.1 */ > > > > - case FFA_NOTIFICATION_BITMAP_CREATE: > > > > - case FFA_NOTIFICATION_BITMAP_DESTROY: > > > > - case FFA_NOTIFICATION_BIND: > > > > - case FFA_NOTIFICATION_UNBIND: > > > > - case FFA_NOTIFICATION_SET: > > > > - case FFA_NOTIFICATION_GET: > > > > - case FFA_NOTIFICATION_INFO_GET: > > > > /* Optional interfaces added in FF-A 1.2 */ > > > > case FFA_MSG_SEND_DIRECT_REQ2: /* Optional per 7.5.1 */ > > > > case FFA_MSG_SEND_DIRECT_RESP2: /* Optional per 7.5.1 */ > > > > > > Shouldn't these be sanitised in a way? A bunch of registers are SBZ in > > > the spec, and I'd expect this to be enforced. > > which still remains unanswered. Missed this sorry. We can reject them in the hyp proxy if the caller uses non zero values in those registers. > > M. > > -- > Without deviation from the norm, progress is not possible. Thanks, Sebastian