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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-532eb38d347sm47450101cf.25.2026.09.24.11.00.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 11:00:21 -0700 (PDT) Date: Thu, 24 Sep 2026 14:00:18 -0400 From: Gregory Price To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, linux-rdma@vger.kernel.org, selinux@vger.kernel.org, linux-sound@vger.kernel.org, bpf@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev Subject: Re: [PATCH v3 05/40] mm/vma: ensure mmap_prepare doesn't set actions on a mergeable vma Message-ID: References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-5-4583d8a23bca@kernel.org> Precedence: bulk X-Mailing-List: linux-fbdev@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: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-5-4583d8a23bca@kernel.org> On Thu, Sep 17, 2026 at 05:22:14PM +0100, Lorenzo Stoakes (ARM) wrote: > When a user requests an mmap_action be performed in mmap_prepare, this > involves populating the VMA range with data. > > However, if the VMA is mergeable, it might then mistakenly be merged with > another VMA without having populated the range. > > Every mmap action currently available sets VMA flags such that the VMA > cannot be merged. > > However, to ensure that no future mmap action falls foul of this, assert > that this is the case upon mmap_prepare validation. > > Signed-off-by: Lorenzo Stoakes (ARM) > --- > mm/vma.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/vma.c b/mm/vma.c > index d6ed10cefc8f..62f2ce1ad5a1 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -2809,6 +2809,15 @@ static int mmap_validate(unsigned long prev_start, unsigned long prev_end, > int mmap_prepare_validate(const struct vm_area_desc *prev_desc, > const struct vm_area_desc *desc) > { > + /* > + * It is not valid to execute mmap actions for VMAs which can be merged, > + * as any such merge would leave portions of the mapping incorrectly > + * unmapped. > + */ > + if (vma_flags_can_merge(&desc->vma_flags) && > + WARN_ON_ONCE(desc->action.type != MMAP_NOTHING)) > + return -EINVAL; > + If you wanted to make this unit-testable, you could pull it out into a separate function: static bool mmap_action_is_valid(const struct vm_area_desc *desc) { return desc->action.type == MMAP_NOTHING || !vma_flags_can_merge(&desc->vma_flags); } then write: if (WARN_ON_ONCE(!mmap_action_is_valid(desc))) return -EINVAL; And you can write a unit test directly against mmap_action_is_valid otherwise Reviewed-by: Gregory Price (Meta) 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 25B65C9830E for ; Thu, 24 Sep 2026 18:00:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; 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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-532eb38d347sm47450101cf.25.2026.09.24.11.00.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 11:00:21 -0700 (PDT) Date: Thu, 24 Sep 2026 14:00:18 -0400 From: Gregory Price To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, linux-rdma@vger.kernel.org, selinux@vger.kernel.org, linux-sound@vger.kernel.org, bpf@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev Subject: Re: [PATCH v3 05/40] mm/vma: ensure mmap_prepare doesn't set actions on a mergeable vma Message-ID: References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-5-4583d8a23bca@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-5-4583d8a23bca@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260924_110023_374960_DD994E62 X-CRM114-Status: GOOD ( 20.43 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Thu, Sep 17, 2026 at 05:22:14PM +0100, Lorenzo Stoakes (ARM) wrote: > When a user requests an mmap_action be performed in mmap_prepare, this > involves populating the VMA range with data. > > However, if the VMA is mergeable, it might then mistakenly be merged with > another VMA without having populated the range. > > Every mmap action currently available sets VMA flags such that the VMA > cannot be merged. > > However, to ensure that no future mmap action falls foul of this, assert > that this is the case upon mmap_prepare validation. > > Signed-off-by: Lorenzo Stoakes (ARM) > --- > mm/vma.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/vma.c b/mm/vma.c > index d6ed10cefc8f..62f2ce1ad5a1 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -2809,6 +2809,15 @@ static int mmap_validate(unsigned long prev_start, unsigned long prev_end, > int mmap_prepare_validate(const struct vm_area_desc *prev_desc, > const struct vm_area_desc *desc) > { > + /* > + * It is not valid to execute mmap actions for VMAs which can be merged, > + * as any such merge would leave portions of the mapping incorrectly > + * unmapped. > + */ > + if (vma_flags_can_merge(&desc->vma_flags) && > + WARN_ON_ONCE(desc->action.type != MMAP_NOTHING)) > + return -EINVAL; > + If you wanted to make this unit-testable, you could pull it out into a separate function: static bool mmap_action_is_valid(const struct vm_area_desc *desc) { return desc->action.type == MMAP_NOTHING || !vma_flags_can_merge(&desc->vma_flags); } then write: if (WARN_ON_ONCE(!mmap_action_is_valid(desc))) return -EINVAL; And you can write a unit test directly against mmap_action_is_valid otherwise Reviewed-by: Gregory Price (Meta) _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv 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 2637DC98321 for ; 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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-532eb38d347sm47450101cf.25.2026.09.24.11.00.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2026 11:00:21 -0700 (PDT) Date: Thu, 24 Sep 2026 14:00:18 -0400 From: Gregory Price To: "Lorenzo Stoakes (ARM)" Cc: Andrew Morton , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-usb@vger.kernel.org, linux-rdma@vger.kernel.org, selinux@vger.kernel.org, linux-sound@vger.kernel.org, bpf@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-trace-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, fuse-devel@lists.linux.dev Subject: Re: [PATCH v3 05/40] mm/vma: ensure mmap_prepare doesn't set actions on a mergeable vma Message-ID: References: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-0-4583d8a23bca@kernel.org> <20260917-b4-mmap-prepare-vma-flag-sanify-v3-5-4583d8a23bca@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20260917-b4-mmap-prepare-vma-flag-sanify-v3-5-4583d8a23bca@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260924_110023_375458_6D8BA8F9 X-CRM114-Status: GOOD ( 20.43 ) X-BeenThere: kvm-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kvm-riscv" Errors-To: kvm-riscv-bounces+kvm-riscv=archiver.kernel.org@lists.infradead.org On Thu, Sep 17, 2026 at 05:22:14PM +0100, Lorenzo Stoakes (ARM) wrote: > When a user requests an mmap_action be performed in mmap_prepare, this > involves populating the VMA range with data. > > However, if the VMA is mergeable, it might then mistakenly be merged with > another VMA without having populated the range. > > Every mmap action currently available sets VMA flags such that the VMA > cannot be merged. > > However, to ensure that no future mmap action falls foul of this, assert > that this is the case upon mmap_prepare validation. > > Signed-off-by: Lorenzo Stoakes (ARM) > --- > mm/vma.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/vma.c b/mm/vma.c > index d6ed10cefc8f..62f2ce1ad5a1 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -2809,6 +2809,15 @@ static int mmap_validate(unsigned long prev_start, unsigned long prev_end, > int mmap_prepare_validate(const struct vm_area_desc *prev_desc, > const struct vm_area_desc *desc) > { > + /* > + * It is not valid to execute mmap actions for VMAs which can be merged, > + * as any such merge would leave portions of the mapping incorrectly > + * unmapped. > + */ > + if (vma_flags_can_merge(&desc->vma_flags) && > + WARN_ON_ONCE(desc->action.type != MMAP_NOTHING)) > + return -EINVAL; > + If you wanted to make this unit-testable, you could pull it out into a separate function: static bool mmap_action_is_valid(const struct vm_area_desc *desc) { return desc->action.type == MMAP_NOTHING || !vma_flags_can_merge(&desc->vma_flags); } then write: if (WARN_ON_ONCE(!mmap_action_is_valid(desc))) return -EINVAL; And you can write a unit test directly against mmap_action_is_valid otherwise Reviewed-by: Gregory Price (Meta) -- kvm-riscv mailing list kvm-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kvm-riscv