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 X-Spam-Level: X-Spam-Status: No, score=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D281FC12002 for ; Wed, 21 Jul 2021 10:54:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B505C6146B for ; Wed, 21 Jul 2021 10:54:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237655AbhGUKNA (ORCPT ); Wed, 21 Jul 2021 06:13:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60660 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239801AbhGUKH0 (ORCPT ); Wed, 21 Jul 2021 06:07:26 -0400 Received: from mail-ot1-x332.google.com (mail-ot1-x332.google.com [IPv6:2607:f8b0:4864:20::332]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 21F39C0613DD for ; Wed, 21 Jul 2021 03:46:31 -0700 (PDT) Received: by mail-ot1-x332.google.com with SMTP id b24-20020a9d60d80000b02904d14e47202cso1649075otk.4 for ; Wed, 21 Jul 2021 03:46:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=7lJAFvcjFDxSgk/vkHpYq2yeu+6Zn/sTj2rc7X9M9nU=; b=eZ0Qx+nDEK46aRTYT687jST7ULuil5H1nMXJ5xQbqZ7sHwCdShLdGjKnLwuajBUqaI C1iH1AzEWviiCDZvCotTjUVxhPRzZ09UQKU+SDyvJpcXO0CXw4TiidGE7CkLqJ+so8vf v6t99JHSy8iYHbO3VliujJMF2fhIkF9JBmLhnTSqXVOrOsX9pjbaMiqddYxiwO2B2+ee tjwxcoR5T89IryHyKxEbAA/JSALJgBat+EEKjgu0w7DdRFnDs85HtebCYS6ivlwhItqQ hrNn+J+OeTyu6UARRoaNqPcEZyGK6EixMoFjThLJ2/ba2hKPwkIKB5U/QXrsSvesZcG1 gYiQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=7lJAFvcjFDxSgk/vkHpYq2yeu+6Zn/sTj2rc7X9M9nU=; b=iKnHsv+0Y/3LGOQ/fllI8uKdNgywV5dKiTLxhZFbxEL0rm1IGol0KRpRU7/uYN6LoJ umdz1shSsj9AZBquy2UrDze427X5RQDob7s/iTh8sMEOi2Sg1TOpZja0pwS9fyyqttkQ 9fuj2IADFBbvS/gBdOLUntNfKtU6d8qCw6nvw2qsF5Y2Sp5f53n0VyILy8QDBePiGMV5 88al3Tgg22J7bK2WIYiDufN3k5T6vq/TkmTbjVzl1FKsHMXr6c4Ob/LqZ+DyeY6FUcDW GgUbte95f6N9dZU2nJbWA/tWvdU4Sqq4I9Hcalso8LwhnhDXBtCe/jQWnMvP9ju2bTWz xvag== X-Gm-Message-State: AOAM5317foB7TRJX4FxcQMsO7ibSX4m88zXoZA+eaYynwbkP4p2vHOmF JDLqutCrFkx8S/9sp4/j9wqB1v0m9LDrurL3t6LQFA== X-Google-Smtp-Source: ABdhPJzcshieu8Dzd22Ad1u9ApbpQS9c2D6BVui4kgt8j0A/QaJhDu4uboy6sXNBDRjl6yZadgZqB0ruwbawk/YjT0A= X-Received: by 2002:a9d:600a:: with SMTP id h10mr25212239otj.144.1626864390244; Wed, 21 Jul 2021 03:46:30 -0700 (PDT) MIME-Version: 1.0 References: <20210719104735.3681732-1-qperret@google.com> <20210719104735.3681732-14-qperret@google.com> In-Reply-To: <20210719104735.3681732-14-qperret@google.com> From: Fuad Tabba Date: Wed, 21 Jul 2021 11:45:53 +0100 Message-ID: Subject: Re: [PATCH 13/14] KVM: arm64: Restrict hyp stage-1 manipulation in protected mode To: Quentin Perret Cc: maz@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, ardb@kernel.org, qwandor@google.com, dbrazdil@google.com, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Quentin, On Mon, Jul 19, 2021 at 11:48 AM Quentin Perret wrote: > > The host kernel is currently able to change EL2 stage-1 mappings without > restrictions thanks to the __pkvm_create_mappings() hypercall. But in a > world where the host is no longer part of the TCB, this clearly poses a > problem. > > To fix this, introduce a new hypercall to allow the host to share a > range of physical memory with the hypervisor, and remove the > __pkvm_create_mappings() variant. The new hypercall implements > ownership and permission checks before allowing the sharing operation, > and it annotates the shared pages in the hypervisor stage-1 and host > stage-2 page-tables. > > Signed-off-by: Quentin Perret > --- > arch/arm64/include/asm/kvm_asm.h | 2 +- > arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 + > arch/arm64/kvm/hyp/include/nvhe/mm.h | 2 - > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 12 +- > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 105 ++++++++++++++++++ > arch/arm64/kvm/hyp/nvhe/mm.c | 4 +- > arch/arm64/kvm/mmu.c | 14 ++- > 7 files changed, 124 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h > index 9f0bf2109be7..78db818ae2c9 100644 > --- a/arch/arm64/include/asm/kvm_asm.h > +++ b/arch/arm64/include/asm/kvm_asm.h > @@ -59,7 +59,7 @@ > #define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs 13 > #define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs 14 > #define __KVM_HOST_SMCCC_FUNC___pkvm_init 15 > -#define __KVM_HOST_SMCCC_FUNC___pkvm_create_mappings 16 > +#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp 16 > #define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping 17 > #define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector 18 > #define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize 19 > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > index b39047463075..f37e4d3b831b 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > @@ -22,6 +22,7 @@ extern struct host_kvm host_kvm; > > int __pkvm_prot_finalize(void); > int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end); > +int __pkvm_host_share_hyp(phys_addr_t start, phys_addr_t end); > > int host_stage2_idmap_locked(u64 start, u64 end, enum kvm_pgtable_prot prot); > int kvm_host_prepare_stage2(void *pgt_pool_base); > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h > index c76d7136ed9b..c9a8f535212e 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mm.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h > @@ -24,8 +24,6 @@ int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back); > int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot); > int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot); > int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot); > -int __pkvm_create_mappings(unsigned long start, unsigned long size, > - unsigned long phys, enum kvm_pgtable_prot prot); > unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size, > enum kvm_pgtable_prot prot); > > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index 1632f001f4ed..f05ecbd382d0 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -140,14 +140,12 @@ static void handle___pkvm_cpu_set_vector(struct kvm_cpu_context *host_ctxt) > cpu_reg(host_ctxt, 1) = pkvm_cpu_set_vector(slot); > } > > -static void handle___pkvm_create_mappings(struct kvm_cpu_context *host_ctxt) > +static void handle___pkvm_host_share_hyp(struct kvm_cpu_context *host_ctxt) > { > - DECLARE_REG(unsigned long, start, host_ctxt, 1); > - DECLARE_REG(unsigned long, size, host_ctxt, 2); > - DECLARE_REG(unsigned long, phys, host_ctxt, 3); > - DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 4); > + DECLARE_REG(phys_addr_t, start, host_ctxt, 1); > + DECLARE_REG(phys_addr_t, end, host_ctxt, 2); > > - cpu_reg(host_ctxt, 1) = __pkvm_create_mappings(start, size, phys, prot); > + cpu_reg(host_ctxt, 1) = __pkvm_host_share_hyp(start, end); > } > > static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ctxt) > @@ -193,7 +191,7 @@ static const hcall_t host_hcall[] = { > HANDLE_FUNC(__vgic_v3_restore_aprs), > HANDLE_FUNC(__pkvm_init), > HANDLE_FUNC(__pkvm_cpu_set_vector), > - HANDLE_FUNC(__pkvm_create_mappings), > + HANDLE_FUNC(__pkvm_host_share_hyp), > HANDLE_FUNC(__pkvm_create_private_mapping), > HANDLE_FUNC(__pkvm_prot_finalize), > HANDLE_FUNC(__pkvm_mark_hyp), > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > index 6f28edf58407..20b3cb3fdc67 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > @@ -262,6 +262,111 @@ static int host_stage2_idmap(u64 addr) > return ret; > } > > +static int hyp_range_is_shared_walker(u64 addr, u64 end, u32 level, > + kvm_pte_t *ptep, > + enum kvm_pgtable_walk_flags flag, > + void * const arg) > +{ > + enum kvm_pgtable_prot prot; > + kvm_pte_t pte = *ptep; > + > + if (!kvm_pte_valid(pte)) > + return -EPERM; > + > + prot = kvm_pgtable_hyp_pte_prot(pte); > + if (!prot) > + return -EPERM; nit: is this check necessary? > + /* Check that the page has been shared with the hypervisor before */ > + if (prot != (PAGE_HYP | KVM_PGTABLE_STATE_SHARED | KVM_PGTABLE_STATE_BORROWED)) > + return -EPERM; > + > + return 0; > +} > + > +static int hyp_range_is_shared(phys_addr_t start, phys_addr_t end) > +{ > + struct kvm_pgtable_walker walker = { > + .cb = hyp_range_is_shared_walker, > + .flags = KVM_PGTABLE_WALK_LEAF, > + }; > + > + return kvm_pgtable_walk(&pkvm_pgtable, (u64)__hyp_va(start), > + end - start, &walker); > +} > + > +static int check_host_share_hyp_walker(u64 addr, u64 end, u32 level, nit: It seems the convention is usually addr,size or start,end. Here you're using addr,end. > + kvm_pte_t *ptep, > + enum kvm_pgtable_walk_flags flag, > + void * const arg) > +{ > + enum kvm_pgtable_prot prot; > + kvm_pte_t pte = *ptep; > + > + /* If invalid, only allow to share pristine pages */ > + if (!kvm_pte_valid(pte)) > + return pte ? -EPERM : 0; > + > + prot = kvm_pgtable_stage2_pte_prot(pte); > + if (!prot) > + return -EPERM; > + > + /* Cannot share a page that is not owned */ > + if (prot & KVM_PGTABLE_STATE_BORROWED) > + return -EPERM; > + > + /* Cannot share a page with restricted access */ > + if ((prot & KVM_PGTABLE_PROT_RWX) ^ KVM_PGTABLE_PROT_RWX) nit: isn't this clearer as if ((prot & KVM_PGTABLE_PROT_RWX) != KVM_PGTABLE_PROT_RWX) > + return -EPERM; > + > + /* Allow double-sharing (requires cross-checking the hyp stage-1) */ > + if (prot & KVM_PGTABLE_STATE_SHARED) > + return hyp_range_is_shared(addr, addr + 1); Why addr+1, rather than end? > + > + return 0; > +} > + > +static int check_host_share_hyp(phys_addr_t start, phys_addr_t end) > +{ > + struct kvm_pgtable_walker walker = { > + .cb = check_host_share_hyp_walker, > + .flags = KVM_PGTABLE_WALK_LEAF, > + }; > + > + return kvm_pgtable_walk(&host_kvm.pgt, start, end - start, &walker); > +} > + > +int __pkvm_host_share_hyp(phys_addr_t start, phys_addr_t end) > +{ > + enum kvm_pgtable_prot prot; > + int ret; > + > + if (!range_is_memory(start, end)) > + return -EINVAL; > + > + hyp_spin_lock(&host_kvm.lock); > + hyp_spin_lock(&pkvm_pgd_lock); > + > + ret = check_host_share_hyp(start, end); > + if (ret) > + goto unlock; > + > + prot = KVM_PGTABLE_PROT_RWX | KVM_PGTABLE_STATE_SHARED; > + ret = host_stage2_idmap_locked(start, end, prot); Just for me to understand this better. The id mapping here, which wasn't taking place before this patch, is for tracking, right? Thanks, /fuad > + if (ret && ret != -EAGAIN) > + goto unlock; > + > + prot = PAGE_HYP | KVM_PGTABLE_STATE_SHARED | KVM_PGTABLE_STATE_BORROWED; > + ret = pkvm_create_mappings_locked(__hyp_va(start), __hyp_va(end), prot); > + /* XXX - undo host stage-2 changes if ret != 0 */ > + > +unlock: > + hyp_spin_unlock(&pkvm_pgd_lock); > + hyp_spin_unlock(&host_kvm.lock); > + > + return ret; > +} > + > int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end) > { > int ret; > diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c > index dde22e2a322a..95f6c34a38ec 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mm.c > +++ b/arch/arm64/kvm/hyp/nvhe/mm.c > @@ -23,8 +23,8 @@ u64 __io_map_base; > struct memblock_region hyp_memory[HYP_MEMBLOCK_REGIONS]; > unsigned int hyp_memblock_nr; > > -int __pkvm_create_mappings(unsigned long start, unsigned long size, > - unsigned long phys, enum kvm_pgtable_prot prot) > +static int __pkvm_create_mappings(unsigned long start, unsigned long size, > + unsigned long phys, enum kvm_pgtable_prot prot) > { > int err; > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 0625bf2353c2..2158d1e00acd 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -259,10 +259,8 @@ static int __create_hyp_mappings(unsigned long start, unsigned long size, > { > int err; > > - if (!kvm_host_owns_hyp_mappings()) { > - return kvm_call_hyp_nvhe(__pkvm_create_mappings, > - start, size, phys, prot); > - } > + if (WARN_ON(!kvm_host_owns_hyp_mappings())) > + return -EINVAL; > > mutex_lock(&kvm_hyp_pgd_mutex); > err = kvm_pgtable_hyp_map(hyp_pgtable, start, size, phys, prot); > @@ -302,6 +300,14 @@ int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot) > if (is_kernel_in_hyp_mode()) > return 0; > > + if (!kvm_host_owns_hyp_mappings()) { > + if (WARN_ON(prot != PAGE_HYP)) > + return -EPERM; > + return kvm_call_hyp_nvhe(__pkvm_host_share_hyp, > + kvm_kaddr_to_phys(from), > + kvm_kaddr_to_phys(to)); > + } > + > start = start & PAGE_MASK; > end = PAGE_ALIGN(end); > > -- > 2.32.0.402.g57bb445576-goog > 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 X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED,DKIM_INVALID,DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6F41C12002 for ; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Hi Quentin, On Mon, Jul 19, 2021 at 11:48 AM Quentin Perret wrote: > > The host kernel is currently able to change EL2 stage-1 mappings without > restrictions thanks to the __pkvm_create_mappings() hypercall. But in a > world where the host is no longer part of the TCB, this clearly poses a > problem. > > To fix this, introduce a new hypercall to allow the host to share a > range of physical memory with the hypervisor, and remove the > __pkvm_create_mappings() variant. The new hypercall implements > ownership and permission checks before allowing the sharing operation, > and it annotates the shared pages in the hypervisor stage-1 and host > stage-2 page-tables. > > Signed-off-by: Quentin Perret > --- > arch/arm64/include/asm/kvm_asm.h | 2 +- > arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 + > arch/arm64/kvm/hyp/include/nvhe/mm.h | 2 - > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 12 +- > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 105 ++++++++++++++++++ > arch/arm64/kvm/hyp/nvhe/mm.c | 4 +- > arch/arm64/kvm/mmu.c | 14 ++- > 7 files changed, 124 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h > index 9f0bf2109be7..78db818ae2c9 100644 > --- a/arch/arm64/include/asm/kvm_asm.h > +++ b/arch/arm64/include/asm/kvm_asm.h > @@ -59,7 +59,7 @@ > #define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs 13 > #define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs 14 > #define __KVM_HOST_SMCCC_FUNC___pkvm_init 15 > -#define __KVM_HOST_SMCCC_FUNC___pkvm_create_mappings 16 > +#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp 16 > #define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping 17 > #define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector 18 > #define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize 19 > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > index b39047463075..f37e4d3b831b 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > @@ -22,6 +22,7 @@ extern struct host_kvm host_kvm; > > int __pkvm_prot_finalize(void); > int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end); > +int __pkvm_host_share_hyp(phys_addr_t start, phys_addr_t end); > > int host_stage2_idmap_locked(u64 start, u64 end, enum kvm_pgtable_prot prot); > int kvm_host_prepare_stage2(void *pgt_pool_base); > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h > index c76d7136ed9b..c9a8f535212e 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mm.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h > @@ -24,8 +24,6 @@ int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back); > int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot); > int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot); > int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot); > -int __pkvm_create_mappings(unsigned long start, unsigned long size, > - unsigned long phys, enum kvm_pgtable_prot prot); > unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size, > enum kvm_pgtable_prot prot); > > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index 1632f001f4ed..f05ecbd382d0 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -140,14 +140,12 @@ static void handle___pkvm_cpu_set_vector(struct kvm_cpu_context *host_ctxt) > cpu_reg(host_ctxt, 1) = pkvm_cpu_set_vector(slot); > } > > -static void handle___pkvm_create_mappings(struct kvm_cpu_context *host_ctxt) > +static void handle___pkvm_host_share_hyp(struct kvm_cpu_context *host_ctxt) > { > - DECLARE_REG(unsigned long, start, host_ctxt, 1); > - DECLARE_REG(unsigned long, size, host_ctxt, 2); > - DECLARE_REG(unsigned long, phys, host_ctxt, 3); > - DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 4); > + DECLARE_REG(phys_addr_t, start, host_ctxt, 1); > + DECLARE_REG(phys_addr_t, end, host_ctxt, 2); > > - cpu_reg(host_ctxt, 1) = __pkvm_create_mappings(start, size, phys, prot); > + cpu_reg(host_ctxt, 1) = __pkvm_host_share_hyp(start, end); > } > > static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ctxt) > @@ -193,7 +191,7 @@ static const hcall_t host_hcall[] = { > HANDLE_FUNC(__vgic_v3_restore_aprs), > HANDLE_FUNC(__pkvm_init), > HANDLE_FUNC(__pkvm_cpu_set_vector), > - HANDLE_FUNC(__pkvm_create_mappings), > + HANDLE_FUNC(__pkvm_host_share_hyp), > HANDLE_FUNC(__pkvm_create_private_mapping), > HANDLE_FUNC(__pkvm_prot_finalize), > HANDLE_FUNC(__pkvm_mark_hyp), > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > index 6f28edf58407..20b3cb3fdc67 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > @@ -262,6 +262,111 @@ static int host_stage2_idmap(u64 addr) > return ret; > } > > +static int hyp_range_is_shared_walker(u64 addr, u64 end, u32 level, > + kvm_pte_t *ptep, > + enum kvm_pgtable_walk_flags flag, > + void * const arg) > +{ > + enum kvm_pgtable_prot prot; > + kvm_pte_t pte = *ptep; > + > + if (!kvm_pte_valid(pte)) > + return -EPERM; > + > + prot = kvm_pgtable_hyp_pte_prot(pte); > + if (!prot) > + return -EPERM; nit: is this check necessary? > + /* Check that the page has been shared with the hypervisor before */ > + if (prot != (PAGE_HYP | KVM_PGTABLE_STATE_SHARED | KVM_PGTABLE_STATE_BORROWED)) > + return -EPERM; > + > + return 0; > +} > + > +static int hyp_range_is_shared(phys_addr_t start, phys_addr_t end) > +{ > + struct kvm_pgtable_walker walker = { > + .cb = hyp_range_is_shared_walker, > + .flags = KVM_PGTABLE_WALK_LEAF, > + }; > + > + return kvm_pgtable_walk(&pkvm_pgtable, (u64)__hyp_va(start), > + end - start, &walker); > +} > + > +static int check_host_share_hyp_walker(u64 addr, u64 end, u32 level, nit: It seems the convention is usually addr,size or start,end. Here you're using addr,end. > + kvm_pte_t *ptep, > + enum kvm_pgtable_walk_flags flag, > + void * const arg) > +{ > + enum kvm_pgtable_prot prot; > + kvm_pte_t pte = *ptep; > + > + /* If invalid, only allow to share pristine pages */ > + if (!kvm_pte_valid(pte)) > + return pte ? -EPERM : 0; > + > + prot = kvm_pgtable_stage2_pte_prot(pte); > + if (!prot) > + return -EPERM; > + > + /* Cannot share a page that is not owned */ > + if (prot & KVM_PGTABLE_STATE_BORROWED) > + return -EPERM; > + > + /* Cannot share a page with restricted access */ > + if ((prot & KVM_PGTABLE_PROT_RWX) ^ KVM_PGTABLE_PROT_RWX) nit: isn't this clearer as if ((prot & KVM_PGTABLE_PROT_RWX) != KVM_PGTABLE_PROT_RWX) > + return -EPERM; > + > + /* Allow double-sharing (requires cross-checking the hyp stage-1) */ > + if (prot & KVM_PGTABLE_STATE_SHARED) > + return hyp_range_is_shared(addr, addr + 1); Why addr+1, rather than end? > + > + return 0; > +} > + > +static int check_host_share_hyp(phys_addr_t start, phys_addr_t end) > +{ > + struct kvm_pgtable_walker walker = { > + .cb = check_host_share_hyp_walker, > + .flags = KVM_PGTABLE_WALK_LEAF, > + }; > + > + return kvm_pgtable_walk(&host_kvm.pgt, start, end - start, &walker); > +} > + > +int __pkvm_host_share_hyp(phys_addr_t start, phys_addr_t end) > +{ > + enum kvm_pgtable_prot prot; > + int ret; > + > + if (!range_is_memory(start, end)) > + return -EINVAL; > + > + hyp_spin_lock(&host_kvm.lock); > + hyp_spin_lock(&pkvm_pgd_lock); > + > + ret = check_host_share_hyp(start, end); > + if (ret) > + goto unlock; > + > + prot = KVM_PGTABLE_PROT_RWX | KVM_PGTABLE_STATE_SHARED; > + ret = host_stage2_idmap_locked(start, end, prot); Just for me to understand this better. The id mapping here, which wasn't taking place before this patch, is for tracking, right? Thanks, /fuad > + if (ret && ret != -EAGAIN) > + goto unlock; > + > + prot = PAGE_HYP | KVM_PGTABLE_STATE_SHARED | KVM_PGTABLE_STATE_BORROWED; > + ret = pkvm_create_mappings_locked(__hyp_va(start), __hyp_va(end), prot); > + /* XXX - undo host stage-2 changes if ret != 0 */ > + > +unlock: > + hyp_spin_unlock(&pkvm_pgd_lock); > + hyp_spin_unlock(&host_kvm.lock); > + > + return ret; > +} > + > int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end) > { > int ret; > diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c > index dde22e2a322a..95f6c34a38ec 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mm.c > +++ b/arch/arm64/kvm/hyp/nvhe/mm.c > @@ -23,8 +23,8 @@ u64 __io_map_base; > struct memblock_region hyp_memory[HYP_MEMBLOCK_REGIONS]; > unsigned int hyp_memblock_nr; > > -int __pkvm_create_mappings(unsigned long start, unsigned long size, > - unsigned long phys, enum kvm_pgtable_prot prot) > +static int __pkvm_create_mappings(unsigned long start, unsigned long size, > + unsigned long phys, enum kvm_pgtable_prot prot) > { > int err; > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 0625bf2353c2..2158d1e00acd 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -259,10 +259,8 @@ static int __create_hyp_mappings(unsigned long start, unsigned long size, > { > int err; > > - if (!kvm_host_owns_hyp_mappings()) { > - return kvm_call_hyp_nvhe(__pkvm_create_mappings, > - start, size, phys, prot); > - } > + if (WARN_ON(!kvm_host_owns_hyp_mappings())) > + return -EINVAL; > > mutex_lock(&kvm_hyp_pgd_mutex); > err = kvm_pgtable_hyp_map(hyp_pgtable, start, size, phys, prot); > @@ -302,6 +300,14 @@ int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot) > if (is_kernel_in_hyp_mode()) > return 0; > > + if (!kvm_host_owns_hyp_mappings()) { > + if (WARN_ON(prot != PAGE_HYP)) > + return -EPERM; > + return kvm_call_hyp_nvhe(__pkvm_host_share_hyp, > + kvm_kaddr_to_phys(from), > + kvm_kaddr_to_phys(to)); > + } > + > start = start & PAGE_MASK; > end = PAGE_ALIGN(end); > > -- > 2.32.0.402.g57bb445576-goog > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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 X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_ADSP_CUSTOM_MED,DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8AEDEC636C9 for ; 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Wed, 21 Jul 2021 03:46:30 -0700 (PDT) MIME-Version: 1.0 References: <20210719104735.3681732-1-qperret@google.com> <20210719104735.3681732-14-qperret@google.com> In-Reply-To: <20210719104735.3681732-14-qperret@google.com> From: Fuad Tabba Date: Wed, 21 Jul 2021 11:45:53 +0100 Message-ID: Subject: Re: [PATCH 13/14] KVM: arm64: Restrict hyp stage-1 manipulation in protected mode To: Quentin Perret Cc: maz@kernel.org, james.morse@arm.com, alexandru.elisei@arm.com, suzuki.poulose@arm.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, ardb@kernel.org, qwandor@google.com, dbrazdil@google.com, kernel-team@android.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210721_034634_533937_28AFD1EE X-CRM114-Status: GOOD ( 32.58 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Quentin, On Mon, Jul 19, 2021 at 11:48 AM Quentin Perret wrote: > > The host kernel is currently able to change EL2 stage-1 mappings without > restrictions thanks to the __pkvm_create_mappings() hypercall. But in a > world where the host is no longer part of the TCB, this clearly poses a > problem. > > To fix this, introduce a new hypercall to allow the host to share a > range of physical memory with the hypervisor, and remove the > __pkvm_create_mappings() variant. The new hypercall implements > ownership and permission checks before allowing the sharing operation, > and it annotates the shared pages in the hypervisor stage-1 and host > stage-2 page-tables. > > Signed-off-by: Quentin Perret > --- > arch/arm64/include/asm/kvm_asm.h | 2 +- > arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 + > arch/arm64/kvm/hyp/include/nvhe/mm.h | 2 - > arch/arm64/kvm/hyp/nvhe/hyp-main.c | 12 +- > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 105 ++++++++++++++++++ > arch/arm64/kvm/hyp/nvhe/mm.c | 4 +- > arch/arm64/kvm/mmu.c | 14 ++- > 7 files changed, 124 insertions(+), 16 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h > index 9f0bf2109be7..78db818ae2c9 100644 > --- a/arch/arm64/include/asm/kvm_asm.h > +++ b/arch/arm64/include/asm/kvm_asm.h > @@ -59,7 +59,7 @@ > #define __KVM_HOST_SMCCC_FUNC___vgic_v3_save_aprs 13 > #define __KVM_HOST_SMCCC_FUNC___vgic_v3_restore_aprs 14 > #define __KVM_HOST_SMCCC_FUNC___pkvm_init 15 > -#define __KVM_HOST_SMCCC_FUNC___pkvm_create_mappings 16 > +#define __KVM_HOST_SMCCC_FUNC___pkvm_host_share_hyp 16 > #define __KVM_HOST_SMCCC_FUNC___pkvm_create_private_mapping 17 > #define __KVM_HOST_SMCCC_FUNC___pkvm_cpu_set_vector 18 > #define __KVM_HOST_SMCCC_FUNC___pkvm_prot_finalize 19 > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > index b39047463075..f37e4d3b831b 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > @@ -22,6 +22,7 @@ extern struct host_kvm host_kvm; > > int __pkvm_prot_finalize(void); > int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end); > +int __pkvm_host_share_hyp(phys_addr_t start, phys_addr_t end); > > int host_stage2_idmap_locked(u64 start, u64 end, enum kvm_pgtable_prot prot); > int kvm_host_prepare_stage2(void *pgt_pool_base); > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mm.h b/arch/arm64/kvm/hyp/include/nvhe/mm.h > index c76d7136ed9b..c9a8f535212e 100644 > --- a/arch/arm64/kvm/hyp/include/nvhe/mm.h > +++ b/arch/arm64/kvm/hyp/include/nvhe/mm.h > @@ -24,8 +24,6 @@ int hyp_back_vmemmap(phys_addr_t phys, unsigned long size, phys_addr_t back); > int pkvm_cpu_set_vector(enum arm64_hyp_spectre_vector slot); > int pkvm_create_mappings(void *from, void *to, enum kvm_pgtable_prot prot); > int pkvm_create_mappings_locked(void *from, void *to, enum kvm_pgtable_prot prot); > -int __pkvm_create_mappings(unsigned long start, unsigned long size, > - unsigned long phys, enum kvm_pgtable_prot prot); > unsigned long __pkvm_create_private_mapping(phys_addr_t phys, size_t size, > enum kvm_pgtable_prot prot); > > diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > index 1632f001f4ed..f05ecbd382d0 100644 > --- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c > +++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c > @@ -140,14 +140,12 @@ static void handle___pkvm_cpu_set_vector(struct kvm_cpu_context *host_ctxt) > cpu_reg(host_ctxt, 1) = pkvm_cpu_set_vector(slot); > } > > -static void handle___pkvm_create_mappings(struct kvm_cpu_context *host_ctxt) > +static void handle___pkvm_host_share_hyp(struct kvm_cpu_context *host_ctxt) > { > - DECLARE_REG(unsigned long, start, host_ctxt, 1); > - DECLARE_REG(unsigned long, size, host_ctxt, 2); > - DECLARE_REG(unsigned long, phys, host_ctxt, 3); > - DECLARE_REG(enum kvm_pgtable_prot, prot, host_ctxt, 4); > + DECLARE_REG(phys_addr_t, start, host_ctxt, 1); > + DECLARE_REG(phys_addr_t, end, host_ctxt, 2); > > - cpu_reg(host_ctxt, 1) = __pkvm_create_mappings(start, size, phys, prot); > + cpu_reg(host_ctxt, 1) = __pkvm_host_share_hyp(start, end); > } > > static void handle___pkvm_create_private_mapping(struct kvm_cpu_context *host_ctxt) > @@ -193,7 +191,7 @@ static const hcall_t host_hcall[] = { > HANDLE_FUNC(__vgic_v3_restore_aprs), > HANDLE_FUNC(__pkvm_init), > HANDLE_FUNC(__pkvm_cpu_set_vector), > - HANDLE_FUNC(__pkvm_create_mappings), > + HANDLE_FUNC(__pkvm_host_share_hyp), > HANDLE_FUNC(__pkvm_create_private_mapping), > HANDLE_FUNC(__pkvm_prot_finalize), > HANDLE_FUNC(__pkvm_mark_hyp), > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > index 6f28edf58407..20b3cb3fdc67 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > @@ -262,6 +262,111 @@ static int host_stage2_idmap(u64 addr) > return ret; > } > > +static int hyp_range_is_shared_walker(u64 addr, u64 end, u32 level, > + kvm_pte_t *ptep, > + enum kvm_pgtable_walk_flags flag, > + void * const arg) > +{ > + enum kvm_pgtable_prot prot; > + kvm_pte_t pte = *ptep; > + > + if (!kvm_pte_valid(pte)) > + return -EPERM; > + > + prot = kvm_pgtable_hyp_pte_prot(pte); > + if (!prot) > + return -EPERM; nit: is this check necessary? > + /* Check that the page has been shared with the hypervisor before */ > + if (prot != (PAGE_HYP | KVM_PGTABLE_STATE_SHARED | KVM_PGTABLE_STATE_BORROWED)) > + return -EPERM; > + > + return 0; > +} > + > +static int hyp_range_is_shared(phys_addr_t start, phys_addr_t end) > +{ > + struct kvm_pgtable_walker walker = { > + .cb = hyp_range_is_shared_walker, > + .flags = KVM_PGTABLE_WALK_LEAF, > + }; > + > + return kvm_pgtable_walk(&pkvm_pgtable, (u64)__hyp_va(start), > + end - start, &walker); > +} > + > +static int check_host_share_hyp_walker(u64 addr, u64 end, u32 level, nit: It seems the convention is usually addr,size or start,end. Here you're using addr,end. > + kvm_pte_t *ptep, > + enum kvm_pgtable_walk_flags flag, > + void * const arg) > +{ > + enum kvm_pgtable_prot prot; > + kvm_pte_t pte = *ptep; > + > + /* If invalid, only allow to share pristine pages */ > + if (!kvm_pte_valid(pte)) > + return pte ? -EPERM : 0; > + > + prot = kvm_pgtable_stage2_pte_prot(pte); > + if (!prot) > + return -EPERM; > + > + /* Cannot share a page that is not owned */ > + if (prot & KVM_PGTABLE_STATE_BORROWED) > + return -EPERM; > + > + /* Cannot share a page with restricted access */ > + if ((prot & KVM_PGTABLE_PROT_RWX) ^ KVM_PGTABLE_PROT_RWX) nit: isn't this clearer as if ((prot & KVM_PGTABLE_PROT_RWX) != KVM_PGTABLE_PROT_RWX) > + return -EPERM; > + > + /* Allow double-sharing (requires cross-checking the hyp stage-1) */ > + if (prot & KVM_PGTABLE_STATE_SHARED) > + return hyp_range_is_shared(addr, addr + 1); Why addr+1, rather than end? > + > + return 0; > +} > + > +static int check_host_share_hyp(phys_addr_t start, phys_addr_t end) > +{ > + struct kvm_pgtable_walker walker = { > + .cb = check_host_share_hyp_walker, > + .flags = KVM_PGTABLE_WALK_LEAF, > + }; > + > + return kvm_pgtable_walk(&host_kvm.pgt, start, end - start, &walker); > +} > + > +int __pkvm_host_share_hyp(phys_addr_t start, phys_addr_t end) > +{ > + enum kvm_pgtable_prot prot; > + int ret; > + > + if (!range_is_memory(start, end)) > + return -EINVAL; > + > + hyp_spin_lock(&host_kvm.lock); > + hyp_spin_lock(&pkvm_pgd_lock); > + > + ret = check_host_share_hyp(start, end); > + if (ret) > + goto unlock; > + > + prot = KVM_PGTABLE_PROT_RWX | KVM_PGTABLE_STATE_SHARED; > + ret = host_stage2_idmap_locked(start, end, prot); Just for me to understand this better. The id mapping here, which wasn't taking place before this patch, is for tracking, right? Thanks, /fuad > + if (ret && ret != -EAGAIN) > + goto unlock; > + > + prot = PAGE_HYP | KVM_PGTABLE_STATE_SHARED | KVM_PGTABLE_STATE_BORROWED; > + ret = pkvm_create_mappings_locked(__hyp_va(start), __hyp_va(end), prot); > + /* XXX - undo host stage-2 changes if ret != 0 */ > + > +unlock: > + hyp_spin_unlock(&pkvm_pgd_lock); > + hyp_spin_unlock(&host_kvm.lock); > + > + return ret; > +} > + > int __pkvm_mark_hyp(phys_addr_t start, phys_addr_t end) > { > int ret; > diff --git a/arch/arm64/kvm/hyp/nvhe/mm.c b/arch/arm64/kvm/hyp/nvhe/mm.c > index dde22e2a322a..95f6c34a38ec 100644 > --- a/arch/arm64/kvm/hyp/nvhe/mm.c > +++ b/arch/arm64/kvm/hyp/nvhe/mm.c > @@ -23,8 +23,8 @@ u64 __io_map_base; > struct memblock_region hyp_memory[HYP_MEMBLOCK_REGIONS]; > unsigned int hyp_memblock_nr; > > -int __pkvm_create_mappings(unsigned long start, unsigned long size, > - unsigned long phys, enum kvm_pgtable_prot prot) > +static int __pkvm_create_mappings(unsigned long start, unsigned long size, > + unsigned long phys, enum kvm_pgtable_prot prot) > { > int err; > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 0625bf2353c2..2158d1e00acd 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -259,10 +259,8 @@ static int __create_hyp_mappings(unsigned long start, unsigned long size, > { > int err; > > - if (!kvm_host_owns_hyp_mappings()) { > - return kvm_call_hyp_nvhe(__pkvm_create_mappings, > - start, size, phys, prot); > - } > + if (WARN_ON(!kvm_host_owns_hyp_mappings())) > + return -EINVAL; > > mutex_lock(&kvm_hyp_pgd_mutex); > err = kvm_pgtable_hyp_map(hyp_pgtable, start, size, phys, prot); > @@ -302,6 +300,14 @@ int create_hyp_mappings(void *from, void *to, enum kvm_pgtable_prot prot) > if (is_kernel_in_hyp_mode()) > return 0; > > + if (!kvm_host_owns_hyp_mappings()) { > + if (WARN_ON(prot != PAGE_HYP)) > + return -EPERM; > + return kvm_call_hyp_nvhe(__pkvm_host_share_hyp, > + kvm_kaddr_to_phys(from), > + kvm_kaddr_to_phys(to)); > + } > + > start = start & PAGE_MASK; > end = PAGE_ALIGN(end); > > -- > 2.32.0.402.g57bb445576-goog > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel