From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Xu Date: Tue, 17 Dec 2019 21:56:40 +0000 Subject: Re: [PATCH v4 01/19] KVM: x86: Allocate new rmap and large page tracking when moving memslot Message-Id: <20191217215640.GI7258@xz-x1> List-Id: References: <20191217204041.10815-1-sean.j.christopherson@intel.com> <20191217204041.10815-2-sean.j.christopherson@intel.com> In-Reply-To: <20191217204041.10815-2-sean.j.christopherson@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Sean Christopherson Cc: James Hogan , Paul Mackerras , Christian Borntraeger , Janosch Frank , Paolo Bonzini , Marc Zyngier , linux-arm-kernel@lists.infradead.org, Wanpeng Li , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , kvm@vger.kernel.org, David Hildenbrand , Joerg Roedel , Cornelia Huck , linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, Vitaly Kuznetsov , kvmarm@lists.cs.columbia.edu, Jim Mattson , David Gibson On Tue, Dec 17, 2019 at 12:40:23PM -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(). > > Fixes: 05da45583de9b ("KVM: MMU: large page support") > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson Reviewed-by: Peter Xu I think the error-prone part is: new = old = *slot; Where IMHO it would be better if we only copy pointers explicitly when under control, rather than blindly copying all the pointers in the structure which even contains sub-structures. For example, I see PPC has this: struct kvm_arch_memory_slot { #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE unsigned long *rmap; #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */ }; I started to look into HV code of it a bit, then I see... - kvm_arch_create_memslot(kvmppc_core_create_memslot_hv) init slot->arch.rmap, - kvm_arch_flush_shadow_memslot(kvmppc_core_flush_memslot_hv) didn't free it, - kvm_arch_prepare_memory_region(kvmppc_core_prepare_memory_region_hv) is nop. So Does it have similar issue? -- Peter Xu