From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ed1-f52.google.com (mail-ed1-f52.google.com [209.85.208.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A3B8E3E3C72 for ; Thu, 23 Apr 2026 09:17:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.208.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776935883; cv=none; b=CrcAwdjP5wIKvqmS6q325ENaM/23hsdvN4q2b+UwNT9mK+CKF5oBBf9yJD3Ao5henUBcBsnr8rItoLwK9oKY4EWPPPEevtA9JjQ75nyaKuWo418GIPdTMarwA+5xbptbgJNl4uuWXCrJ9t8Y8P8PHTjyY8QSI9k5ykgVDEloDaM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776935883; c=relaxed/simple; bh=AZoirHf/5mE5YFev+nodzuKCTioKK86YrjX4J7mCnGY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=c3Yk7h8b5LHUggZbvatM7kdjTONgEuCQ5njhISFC76G8PmvM2rpK1EnDARdL/909w7sMJSCr7HSBerISBCyswfprDS7IeDhLWWbFPA8TY7lXQQQbK7oMK+IWoBB9grCAiUTfwPZAd24d24TjKCyC8IjBk7/7bgNS4gD46+Pegec= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=hdaeFEgZ; arc=none smtp.client-ip=209.85.208.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="hdaeFEgZ" Received: by mail-ed1-f52.google.com with SMTP id 4fb4d7f45d1cf-67148a70f8aso49603a12.1 for ; Thu, 23 Apr 2026 02:17:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1776935874; x=1777540674; darn=lists.linux.dev; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=jzw3UnIwHGir8Kj1NlO4m24J9zaCTTh7cxmm2qnVabM=; b=hdaeFEgZP3+p+uYgaH1D8BYetK6VJyAbiEmZA+Y7jMN7a7YoXgmzmDemqEd/NTtooI YKOD9bGbO/sWPq+AItseNg8OEF5sGCHWlnCQdw5E0WScXs6CHnCVRzDDixczpc7IF4tJ QQvkt/FW9+5X4YMTdQoArPQfh4s+Q3qWLmTfAfxUCpSVkGHk6Lab1CSk8DEi9e8RJYfe BS/bs6Bt26ig/tUGiV6WU1j3IAt9Q/dwStlo88MVQ/YlJA59GnS1Ii/Go6sVBbKm5JsG obu8zuLc7FMW5tH3Yj9MFrv1xKdyHhW4EEK9E+YQN/IhOedo60pjGin9piZiYVsNy/m/ RH3Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1776935874; x=1777540674; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=jzw3UnIwHGir8Kj1NlO4m24J9zaCTTh7cxmm2qnVabM=; b=oBM7f/dRzfPCwjOraBf8tVU+PhkqxPfTUqOEklnUx5XOpQDmTzeFcQmonMQhGubsXT p8MyMqeN6mQ/bz4Tyegs1GlMHECKgP4ZMrXKGeENwhG5+hz/VMG74JJIvJ0+9/c1nxtw hpW88ypFIXSKTRjKxnaWIKXLhlOzgA26bZLMPKeqC8PZDOJELYFc9IJ+OEdHGKz8zxYT 92KKf4skHyNWvFCfOKBmbmTc1JVLTWk85lnDoXfwJAPL7vdE6eiDao8Rea5s6jVqt1Io OF7bQp2ju+1dXU/wU/zJ6DAxPa5Q5fO4OzokyHfvqboeKXnKDDRwfZwbyviWIhb5myON DVlQ== X-Forwarded-Encrypted: i=1; AFNElJ9nAg41TZQeXQATH/3iTxJ6yfQCc2PPgz5mlMcL135kgnEBUMJzgB4XQXBjjfKwT4aKfjQz0Bs=@lists.linux.dev X-Gm-Message-State: AOJu0YzCYRNqLX33RzS2v+oU2snyaCLEIzFvX1BoP4iNxrHVatt4OKMh qkL9PN4gLswm8KhA52tg0qmoApFzvy6V1FDz2ijLwoEzQYuhB/ANTGLoOI68TbLImg== X-Gm-Gg: AeBDietGTu8QRyKeWfC0dKBgDdMQrS2L8b17fMMsuOfaeuWonLOtOV4TIQWABgZ9N2O 7cr5Ho9dHnq92g33DJMtZIY8DPioMjjRoJzcQNfluAPYIk9choblRnl54Yno/Upq7PyoqVwXdGq rjO4rnYcNg3lEZoNwuPJFCSR37fSo4FYm0CUy7xK7hT3rD5eNTPFaV6i28piSyFj2C5VlVCYyhn 3LhK9Z4JkM0k/mlc/J4yoExaR8hQecrpcRCDnH8cyaIjQzi7SYJPtt1XGzfeooGL8fjPk2kJPB3 swvGWtsWllVEfesl+bpoBRtQKZ06/5ru9iD5OQbsc9rF1GML+55iYIKLmNoVUFPcvTWbc0O2b8a 9xHlyk65lhqp1jy31VPgoFxiCSPjKMxV+H0a8HyY533qS5GPtLCRoMh4tNAQcpHxHNAms5/5o7u LxxLcB1ijdLscIP+Sdw+/VqFqKcWzxNI1bBw5r+1m35+/wnPN2A9gnljwighe32XdZjXGhJoB01 Eh/xu3YnFozjzBc910= X-Received: by 2002:a05:6402:3085:b0:671:dad9:8caf with SMTP id 4fb4d7f45d1cf-6744ed5f907mr227247a12.5.1776935873820; Thu, 23 Apr 2026 02:17:53 -0700 (PDT) Received: from google.com (117.15.199.104.bc.googleusercontent.com. [104.199.15.117]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-ba451210e49sm655436766b.10.2026.04.23.02.17.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Apr 2026 02:17:53 -0700 (PDT) Date: Thu, 23 Apr 2026 09:17:49 +0000 From: Sebastian Ene To: Sudeep Holla Cc: Marc Zyngier , oupton@kernel.org, will@kernel.org, ayrton@google.com, catalin.marinas@arm.com, 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, yuzenghui@huawei.com, stable@vger.kernel.org Subject: Re: [PATCH] KVM: arm64: Validate the FF-A memory access descriptor placement Message-ID: References: <20260422102540.1433704-1-sebastianene@google.com> <86bjfb18v1.wl-maz@kernel.org> <20260422-jolly-curassow-of-amplitude-25fbaf@sudeepholla> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260422-jolly-curassow-of-amplitude-25fbaf@sudeepholla> On Wed, Apr 22, 2026 at 08:29:06PM +0100, Sudeep Holla wrote: > On Wed, Apr 22, 2026 at 01:35:55PM +0000, Sebastian Ene wrote: > > On Wed, Apr 22, 2026 at 01:24:02PM +0100, Marc Zyngier wrote: > > > On Wed, 22 Apr 2026 11:25:40 +0100, > > > Sebastian Ene wrote: > > > > > > > > Prevent the pKVM hypervisor from making assumptions that the > > > > endpoint memory access descriptor (EMAD) comes right after the > > > > FF-A memory region header and enforce a strict placement for it > > > > when validating an FF-A memory lend/share transaction. > > > > Hello Marc, > > > > > > > > As I read this, you want to remove a bad assumption... > > > > > > > > > > > Prior to FF-A version 1.1 the header of the memory region > > > > didn't contain an offset to the endpoint memory access descriptor. > > > > The layout of a memory transaction looks like this: > > > > > > > > Field name | Offset > > > > -- 0 > > > > [ Header (ffa_mem_region) |__ ep_mem_offset > > > > EMAD 1 (ffa_mem_region_attributes) | > > > > ] > > > > > > > > Reject the host from specifying a memory access descriptor offset > > > > that is different than the size of the memory region header. > > > > > > And yet you decide that you want to enforce this assumption. I don't > > > understand how you arrive to this conclusion. > > > > > > Looking at the spec, it appears that the offset is *designed* to allow > > > a gap between the header and the EMAD. Refusing to handle a it seems to be a > > > violation of the spec. > > > > > > What am I missing? > > > > While the spec allows the gap to be variable (since version 1.1), the > > arm ff-a driver places it at a fixed position in: > > ffa_mem_region_additional_setup() > > https://elixir.bootlin.com/linux/v7.0/source/drivers/firmware/arm_ffa/driver.c#L671 > > > Hello Sudeep, > That's just the current choice in the driver and can be changed in the future. > > > and makes use of the same assumption in: ffa_mem_desc_offset(). > > https://elixir.bootlin.com/linux/v7.0/source/include/linux/arm_ffa.h#L448 > > Again this is just in the transmit path of the message the driver is > constructing and hence it is a simple choice rather than wrong assumption. > > > The later one seems wrong IMO. because we should compute the offset > > based on the value stored in ep_mem_offset and not adding it up with > > sizeof(struct ffa_mem_region). > > > > Sorry what am I missing as the driver is building these descriptors to > send it across to SPMC, we are populating the field and it will be 0 > before it is initialised Right, what I meant is having something like this since this function is not limited to the driver scope and using it from other components would imply relying on the assumption: 'ep_mem_offset == sizeof(struct ffa_mem_region)'. We will also have to validate that the `ep_mem_offset` doesn't point outside of the mailbox designated buffer. --- diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h index 81e603839c4a..62d67dae8b70 100644 --- a/include/linux/arm_ffa.h +++ b/include/linux/arm_ffa.h @@ -445,7 +445,7 @@ ffa_mem_desc_offset(struct ffa_mem_region *buf, int count, u32 ffa_version) if (!FFA_MEM_REGION_HAS_EP_MEM_OFFSET(ffa_version)) offset += offsetof(struct ffa_mem_region, ep_mem_offset); else - offset += sizeof(struct ffa_mem_region); + offset += buf->ep_mem_offset; return offset; } --- And then move `ffa_mem_region_additional_setup` to be called earlier before `ffa_mem_desc_offset`: (so that it can setup the value for ep_mem_offset) --- diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c index f2f94d4d533e..66de59c88aff 100644 --- a/drivers/firmware/arm_ffa/driver.c +++ b/drivers/firmware/arm_ffa/driver.c @@ -691,6 +691,8 @@ ffa_setup_and_transmit(u32 func_id, void *buffer, u32 max_fragsize, mem_region->flags = args->flags; mem_region->sender_id = drv_info->vm_id; mem_region->attributes = ffa_memory_attributes_get(func_id); + + ffa_mem_region_additional_setup(drv_info->version, mem_region); composite_offset = ffa_mem_desc_offset(buffer, args->nattrs, drv_info->version); @@ -708,7 +710,6 @@ ffa_setup_and_transmit(u32 func_id, void *buffer, u32 max_fragsize, } mem_region->handle = 0; mem_region->ep_count = args->nattrs; - ffa_mem_region_additional_setup(drv_info->version, mem_region); --- > > > Maybe this should be the fix instead and not the one in pKVM ? What do > > you think ? > > > > Can you share the diff you have in mind to understand your concern better > or are you referring to this patch itself. Sure, please let me know if you think this is wrong. I might have misunderstood it. > > > The current implementation in pKVM makes use of the > > ffa_mem_desc_offset() to validate the first EMAD. If a compromised host > > places an EMAD at a different offset than sizeof(struct ffa_mem_region), > > then pKVM will not validate that EMAD. > > > > Calling the host as compromised if it chooses a different offset seems bit > of extreme here. I am no sure if I am missing to understand something here. > Sorry for not explaining it, in pKVM model we don't trust the host kernel so we can assume that everything that doesn't pass the hypervisor validation(in this case the ff-a memory transaction) can be a potential attack that wants to compromise EL2. > -- > Regards, > Sudeep Thanks, Sebastian