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[104.199.15.117]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48e65a0fb25sm28858385e9.6.2026.05.08.06.04.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 08 May 2026 06:04:33 -0700 (PDT) Date: Fri, 8 May 2026 13:04:27 +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> <86qznnxptx.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: <86qznnxptx.wl-maz@kernel.org> On Thu, May 07, 2026 at 03:21:46PM +0100, Marc Zyngier wrote: > On Thu, 07 May 2026 15:13:06 +0100, > Sebastian Ene wrote: > > > > 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 > > Does it? How do you verify this? > It is written in the spec under 13.10 FFA_ID_GET ("ID value 0 must be returned at the Non-secure physical FF-A instance"). If this contract is broken and TZ in not spec compliant I am afraid there is not too much that we can do. > > 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 ? > > Let's be clear: I don't give a damn about a potential attack vector. > The moment you add Secure to the mix, security is gone (funny, isn't > it?). I care about being strict about the spec, and not letting > through things that will eventually break. > Understood. > > > > > > > > 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. > > Yes, please. > Ack. > > > > > 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. > > I think we need that indeed. While at it I discovered that none of the FF-A calls in the proxy currently check for these SBZ registers. Would you be ok with a diff that fixes this before the patch with the notifications ? Refactor the handling logic in pKVM FF-A proxy to support checking for SBZ/MBZ values. While at it, drop the do_ffa_mem_xfer macro and replace it with two functions that make it clear that we re-write the function-id with a 64-bit variant, to keep the same behavior as before. Keep each handler in an array of structures together with a mask that corresponds to the SBZ registers the spec expects. diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c index a82d0cd22a17..35443a894172 100644 --- a/arch/arm64/kvm/hyp/nvhe/ffa.c +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c @@ -561,13 +561,6 @@ static void __do_ffa_mem_xfer(const u64 func_id, goto out_unlock; } -#define do_ffa_mem_xfer(fid, res, ctxt) \ - do { \ - BUILD_BUG_ON((fid) != FFA_FN64_MEM_SHARE && \ - (fid) != FFA_FN64_MEM_LEND); \ - __do_ffa_mem_xfer((fid), (res), (ctxt)); \ - } while (0); - static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res, struct kvm_cpu_context *ctxt) { @@ -854,9 +847,60 @@ static void do_ffa_part_get(struct arm_smccc_1_2_regs *res, hyp_spin_unlock(&host_buffers.lock); } +static void do_ffa_mem_share(struct arm_smccc_1_2_regs *res, struct kvm_cpu_context *ctxt) +{ + __do_ffa_mem_xfer(FFA_FN64_MEM_SHARE, res, ctxt); +} + +static void do_ffa_mem_lend(struct arm_smccc_1_2_regs *res, struct kvm_cpu_context *ctxt) +{ + __do_ffa_mem_xfer(FFA_FN64_MEM_LEND, res, ctxt); +} + +struct ffa_handler { + u32 func_id; + void (* do_ffa_handle)(struct arm_smccc_1_2_regs *res, struct kvm_cpu_context *ctxt); + u32 sbz_mask; +}; + +#define REG_RANGE_SBZ GENMASK +#define FFA_HANDLER(fid, cb, sbz) { \ + .func_id = (fid), \ + .do_ffa_handle = (cb), \ + .sbz_mask = (sbz), \ +} + +static const struct ffa_handler host_handlers[] = { + FFA_HANDLER(FFA_FN64_RXTX_MAP, do_ffa_rxtx_map, REG_RANGE_SBZ(17, 4)), + FFA_HANDLER(FFA_RXTX_UNMAP, do_ffa_rxtx_unmap, REG_RANGE_SBZ(17, 2)), + FFA_HANDLER(FFA_MEM_SHARE, do_ffa_mem_share, REG_RANGE_SBZ(17, 5)), + FFA_HANDLER(FFA_FN64_MEM_SHARE, do_ffa_mem_share, REG_RANGE_SBZ(17, 5)), + FFA_HANDLER(FFA_MEM_RECLAIM, do_ffa_mem_reclaim, REG_RANGE_SBZ(17, 4)), + FFA_HANDLER(FFA_MEM_LEND, do_ffa_mem_lend, REG_RANGE_SBZ(17, 5)), + FFA_HANDLER(FFA_FN64_MEM_LEND, do_ffa_mem_lend, REG_RANGE_SBZ(17, 5)), + FFA_HANDLER(FFA_MEM_FRAG_TX, do_ffa_mem_frag_tx, REG_RANGE_SBZ(17, 5)), + FFA_HANDLER(FFA_VERSION, do_ffa_version, REG_RANGE_SBZ(17, 2)), + FFA_HANDLER(FFA_PARTITION_INFO_GET, do_ffa_part_get, REG_RANGE_SBZ(17, 6)), +}; + +static bool is_sbz_error(const struct ffa_handler *cb, struct kvm_cpu_context *ctxt) +{ + int reg_idx, reg_end = fls(cb->sbz_mask); + + if (!ARM_SMCCC_IS_64(cb->func_id) && reg_end > 7) + reg_end = 7; + + for (reg_idx = 0; reg_idx <= reg_end; reg_idx++) + if (((BIT(reg_idx) & cb->sbz_mask)) && cpu_reg(ctxt, reg_idx)) + return true; + + return false; +} + bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id) { struct arm_smccc_1_2_regs res; + const struct ffa_handler *cb; /* * There's no way we can tell what a non-standard SMC call might @@ -880,37 +924,22 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id) goto out_handled; } - switch (func_id) { - case FFA_FEATURES: + if (func_id == FFA_FEATURES) { if (!do_ffa_features(&res, host_ctxt)) return false; goto out_handled; - /* Memory management */ - case FFA_FN64_RXTX_MAP: - do_ffa_rxtx_map(&res, host_ctxt); - goto out_handled; - case FFA_RXTX_UNMAP: - do_ffa_rxtx_unmap(&res, host_ctxt); - goto out_handled; - case FFA_MEM_SHARE: - case FFA_FN64_MEM_SHARE: - do_ffa_mem_xfer(FFA_FN64_MEM_SHARE, &res, host_ctxt); - goto out_handled; - case FFA_MEM_RECLAIM: - do_ffa_mem_reclaim(&res, host_ctxt); - goto out_handled; - case FFA_MEM_LEND: - case FFA_FN64_MEM_LEND: - do_ffa_mem_xfer(FFA_FN64_MEM_LEND, &res, host_ctxt); - goto out_handled; - case FFA_MEM_FRAG_TX: - do_ffa_mem_frag_tx(&res, host_ctxt); - goto out_handled; - case FFA_VERSION: - do_ffa_version(&res, host_ctxt); - goto out_handled; - case FFA_PARTITION_INFO_GET: - do_ffa_part_get(&res, host_ctxt); + } + + for (cb = host_handlers; cb < host_handlers + ARRAY_SIZE(host_handlers); cb++) { + if (cb->func_id != func_id) + continue; + + if (is_sbz_error(cb, host_ctxt)) { + ffa_to_smccc_error(&res, FFA_RET_INVALID_PARAMETERS); + goto out_handled; + } + + cb->do_ffa_handle(&res, host_ctxt); goto out_handled; } -- 2.54.0.563.g4f69b47b94-goog > > M. > > -- > Without deviation from the norm, progress is not possible. Thanks, Sebastian