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Wed, 05 Feb 2020 13:49:55 -0800 (PST) Received: from xz-x1 ([2607:9880:19c8:32::2]) by smtp.gmail.com with ESMTPSA id x11sm472147qkf.50.2020.02.05.13.49.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Feb 2020 13:49:55 -0800 (PST) Date: Wed, 5 Feb 2020 16:49:52 -0500 From: Peter Xu To: Sean Christopherson Subject: Re: [PATCH v5 01/19] KVM: x86: Allocate new rmap and large page tracking when moving memslot Message-ID: <20200205214952.GD387680@xz-x1> References: <20200121223157.15263-1-sean.j.christopherson@intel.com> <20200121223157.15263-2-sean.j.christopherson@intel.com> MIME-Version: 1.0 In-Reply-To: <20200121223157.15263-2-sean.j.christopherson@intel.com> X-MC-Unique: nxkxZtK9OJ6NC9MKQI6T0Q-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: Wanpeng Li , kvm@vger.kernel.org, David Hildenbrand , linux-mips@vger.kernel.org, Paul Mackerras , kvmarm@lists.cs.columbia.edu, Janosch Frank , Marc Zyngier , Joerg Roedel , Christian Borntraeger , kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jim Mattson , Cornelia Huck , linux-kernel@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Tue, Jan 21, 2020 at 02:31:39PM -0800, Sean Christopherson wrote: > Reallocate a rmap array and recalcuate large page compatibility when > moving an existing memslot to correctly handle the alignment properties > of the new memslot. The number of rmap entries required at each level > is dependent on the alignment of the memslot's base gfn with respect to > that level, e.g. moving a large-page aligned memslot so that it becomes > unaligned will increase the number of rmap entries needed at the now > unaligned level. > > Not updating the rmap array is the most obvious bug, as KVM accesses > garbage data beyond the end of the rmap. KVM interprets the bad data as > pointers, leading to non-canonical #GPs, unexpected #PFs, etc... > > general protection fault: 0000 [#1] SMP > CPU: 0 PID: 1909 Comm: move_memory_reg Not tainted 5.4.0-rc7+ #139 > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 > RIP: 0010:rmap_get_first+0x37/0x50 [kvm] > Code: <48> 8b 3b 48 85 ff 74 ec e8 6c f4 ff ff 85 c0 74 e3 48 89 d8 5b c3 > RSP: 0018:ffffc9000021bbc8 EFLAGS: 00010246 > RAX: ffff00617461642e RBX: ffff00617461642e RCX: 0000000000000012 > RDX: ffff88827400f568 RSI: ffffc9000021bbe0 RDI: ffff88827400f570 > RBP: 0010000000000000 R08: ffffc9000021bd00 R09: ffffc9000021bda8 > R10: ffffc9000021bc48 R11: 0000000000000000 R12: 0030000000000000 > R13: 0000000000000000 R14: ffff88827427d700 R15: ffffc9000021bce8 > FS: 00007f7eda014700(0000) GS:ffff888277a00000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f7ed9216ff8 CR3: 0000000274391003 CR4: 0000000000162eb0 > Call Trace: > kvm_mmu_slot_set_dirty+0xa1/0x150 [kvm] > __kvm_set_memory_region.part.64+0x559/0x960 [kvm] > kvm_set_memory_region+0x45/0x60 [kvm] > kvm_vm_ioctl+0x30f/0x920 [kvm] > do_vfs_ioctl+0xa1/0x620 > ksys_ioctl+0x66/0x70 > __x64_sys_ioctl+0x16/0x20 > do_syscall_64+0x4c/0x170 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > RIP: 0033:0x7f7ed9911f47 > Code: <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 21 6f 2c 00 f7 d8 64 89 01 48 > RSP: 002b:00007ffc00937498 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 0000000001ab0010 RCX: 00007f7ed9911f47 > RDX: 0000000001ab1350 RSI: 000000004020ae46 RDI: 0000000000000004 > RBP: 000000000000000a R08: 0000000000000000 R09: 00007f7ed9214700 > R10: 00007f7ed92149d0 R11: 0000000000000246 R12: 00000000bffff000 > R13: 0000000000000003 R14: 00007f7ed9215000 R15: 0000000000000000 > Modules linked in: kvm_intel kvm irqbypass > ---[ end trace 0c5f570b3358ca89 ]--- > > The disallow_lpage tracking is more subtle. Failure to update results > in KVM creating large pages when it shouldn't, either due to stale data > or again due to indexing beyond the end of the metadata arrays, which > can lead to memory corruption and/or leaking data to guest/userspace. > > Note, the arrays for the old memslot are freed by the unconditional call > to kvm_free_memslot() in __kvm_set_memory_region(). If __kvm_set_memory_region() failed, I think the old memslot will be kept and the new memslot will be freed instead? > > Fixes: 05da45583de9b ("KVM: MMU: large page support") > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/x86.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 4c30ebe74e5d..1953c71c52f2 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -9793,6 +9793,13 @@ int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot, > { > int i; > > + /* > + * Clear out the previous array pointers for the KVM_MR_MOVE case. The > + * old arrays will be freed by __kvm_set_memory_region() if installing > + * the new memslot is successful. > + */ > + memset(&slot->arch, 0, sizeof(slot->arch)); I actually gave r-b on this patch but it was lost... And then when I read it again I start to confuse on why we need to set these to zeros. Even if they're not zeros, iiuc kvm_free_memslot() will compare each of the array pointer and it will only free the changed pointers, then it looks fine even without zeroing? > + > for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) { > struct kvm_lpage_info *linfo; > unsigned long ugfn; > @@ -9867,6 +9874,10 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > const struct kvm_userspace_memory_region *mem, > enum kvm_mr_change change) > { > + if (change == KVM_MR_MOVE) > + return kvm_arch_create_memslot(kvm, memslot, > + mem->memory_size >> PAGE_SHIFT); > + Instead of calling kvm_arch_create_memslot() explicitly again here, can it be replaced by below? diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 72b45f491692..85a7b02fd752 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1144,7 +1144,7 @@ int __kvm_set_memory_region(struct kvm *kvm, new.dirty_bitmap = NULL; r = -ENOMEM; - if (change == KVM_MR_CREATE) { + if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) { new.userspace_addr = mem->userspace_addr; if (kvm_arch_create_memslot(kvm, &new, npages)) > return 0; > } > > -- > 2.24.1 > -- Peter Xu _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm