lkml.org 
[lkml]   [2019]   [Dec]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v4 01/19] KVM: x86: Allocate new rmap and large page tracking when moving memslot
Dropping non-x86 folks...

This should be included in 5.5 if possible even though the bug has existed
for over a decade. It's trivially easy for a malicious userspace to
crash KVM and hang the host. Depending how userspace VMM behavior, it may
even be possible to trigger from a guest.

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 <sean.j.christopherson@intel.com>
> ---
> 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 8bb2fb1705ff..04d1bf89da0e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9703,6 +9703,13 @@ 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));
> +
> for (i = 0; i < KVM_NR_PAGE_SIZES; ++i) {
> struct kvm_lpage_info *linfo;
> unsigned long ugfn;
> @@ -9777,6 +9784,10 @@ 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);
> +
> return 0;
> }
>
> --
> 2.24.1
>

\
 
 \ /
  Last update: 2019-12-17 21:48    [W:0.175 / U:34.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site