From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 20F75C982C1 for ; Wed, 16 Sep 2026 16:39:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=qbUkCe6/Hy5YMIMHuDCsF2qVBQnZjqVmCyW7U93VnXM=; b=U7P4fisjI+c+A1qQ/OnXErlZRH oIU90XzU60EGkAEyQy6ZtoLcwfcXiOXqvDUeAkTO9XsKwARMRKg2vWrrLR3lkUYAQhagYAzyB18Qu d/jLn5j/SP9tZgFmbm6WXIRZU4260929MJKS8d5KQn1+DYKGoXl5buNLqHl2IxJGMEUbBUvL1MNTj OYhjVUL6VRJK040Nre3goUAEAOId+/4wkWcMGIcYsqyg/NGP7Ty5PuKmOtgNgRJpV/eAPBAxKbjZ7 WTD1VIXAPx6I4GNd/upEpJ+8do3is2H7gbz1PXO2zIDIxhm/lKouU62EZgFOI07bNDY6JmbfpnEuq DBRgdQhg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6sfX-00000009lNk-0cy1; Wed, 16 Sep 2026 16:39:35 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1x6sfT-00000009lMv-4A0M for linux-arm-kernel@lists.infradead.org; Wed, 16 Sep 2026 16:39:33 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8B9A41516; Wed, 16 Sep 2026 09:39:26 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8E2973F7B4; Wed, 16 Sep 2026 09:39:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1789576770; bh=tpRIZijp9OVz8xJ1EeL+tPf3ChFeQoiLXmvmWlNF4Eg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VTTpRpO/bXvOGdJEE2whk8i4bgjlyM4Oe4CK8N8HAJRuPmsS+tN8MXN42RXbgm3Sc f6K3/OxKnrKjaSuMPpqKf/X+YxnbfWi+9aQ4r9mef1QEHKjGlliCtpz9+wMnNi2U8l fztfrqPEyKMI4cNjC0OP4zktopb5mSoOGIwd3hPw= Date: Wed, 16 Sep 2026 17:39:24 +0100 From: Catalin Marinas To: Suzuki K Poulose Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, maz@kernel.org, will@kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, steven.price@arm.com, aneesh.kumar@kernel.org, oupton@kernel.org, gshan@redhat.com, joey.gouly@arm.com, tabba@google.com, yuzenghui@huawei.com, linux-coco@lists.linux.dev, gankulkarni@os.amperecomputing.com, sdonthineni@nvidia.com, alpergun@google.com, fj0570is@fujitsu.com, WeiLin.Chang@arm.com, lpieralisi@kernel.org, enju.kohei@fujitsu.com Subject: Re: [PATCH v18] arm64: mm: Handle Granule Protection Faults (GPFs) Message-ID: References: <20260913070459.2547407-1-suzuki.poulose@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260913070459.2547407-1-suzuki.poulose@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260916_093932_116043_1E134AD5 X-CRM114-Status: GOOD ( 30.77 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Sun, Sep 13, 2026 at 08:04:58AM +0100, Suzuki K Poulose wrote: > From: Steven Price > > If the host attempts to access granules that have been delegated for use > in a realm these accesses will be caught and will trigger a Granule > Protection Fault (GPF). > > A fault during a page walk signals a bug in the kernel and is handled by > oopsing the kernel. A non-page walk fault could be caused by user space > having access to a page which has been delegated to the kernel and will > trigger a SIGBUS to allow debugging why user space is trying to access a > delegated page. > > There is work in progress to unmap the guest_memfd backed private pages from the > linear map. Until we get that support, we could get spurious GPFs from within > the kernel, e.g., load_unaligned_zeropad(). So, try to fix them up for now. > > Reviewed-by: Suzuki K Poulose > Reviewed-by: Gavin Shan > Reviewed-by: Catalin Marinas > Signed-off-by: Steven Price > Signed-off-by: Suzuki K Poulose > --- > Changes since v17: > * Pass untagged address to die_kernel_fault() - Sashiko > * Explicitly check !user_mode() for fixups - Catalin > * Switch to BUS_OBJERR for si_code from SI_KERNEL - Catalin > * Clarify the commit description about the upcoming work on > unmapping guest_memfd backed pages from linear map > Changes since v16: > * Update the commit description to indicate why we try to fixup GPFs > Changes since v10: > * Don't call arm64_notify_die() in do_gpf() but simply return 1. > Changes since v2: > * Include missing "Granule Protection Fault at level -1" > --- > arch/arm64/mm/fault.c | 30 ++++++++++++++++++++++++------ > 1 file changed, 24 insertions(+), 6 deletions(-) > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index 75c3e463df2ef..dc3a87902a60c 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -914,6 +914,24 @@ static int do_tag_check_fault(unsigned long far, unsigned long esr, > return 0; > } > > +static int do_gpf_ptw(unsigned long far, unsigned long esr, struct pt_regs *regs) > +{ > + const struct fault_info *inf = esr_to_fault_info(esr); > + unsigned long addr = untagged_addr(far); > + > + die_kernel_fault(inf->name, addr, esr, regs); > + return 0; > +} > + > +static int do_gpf(unsigned long far, unsigned long esr, struct pt_regs *regs) > +{ > + if (!user_mode(regs) && !is_el1_instruction_abort(esr) && > + fixup_exception(regs, esr)) > + return 0; > + > + return 1; > +} We discussed briefly offline. With the latest patches around, would we ever end up with private memory mapped in the VMM and hence the GPF? If not, I would still keep this handling but add a WARN_ON_ONCE(user_mode(regs)). However, can we end up delegating a non-guest_memfd memslot page as protected? I played a bit with codex and it reckons it's possible if a guest_memfd memslot is deleted after its IPA range has been initialised with RIPAS=RAM. Removing the memslot unmaps and undelegates any data pages but leaves the RMM state as RAM. The VMM can then install an ordinary memslot over the same GPA range. A subsequent private-IPA S2 fault sees the non-guest_memfd slot, takes user_mem_abort(), GUPs the user page and passes it to realm_map_protected(). The userspace mapping remains present, so a later EL0 access can generate a GPF. What's worse, I think it can even trick the kernel into doing a memcpy() access (via GUP). Hmm, does such ordinary slot page even remain pinned? There are other kernel parts that could access it. I don't think it changes this patch but if the above is possible, we should definitely get it tightened on the other series (and here we can add the warning). -- Catalin