KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect()

KASAN reports the following issue:

 BUG: KASAN: stack-out-of-bounds in kvm_make_vcpus_request_mask+0x174/0x440 [kvm]
 Read of size 8 at addr ffffc9001364f638 by task qemu-kvm/4798

 CPU: 0 PID: 4798 Comm: qemu-kvm Tainted: G               X --------- ---
 Hardware name: AMD Corporation DAYTONA_X/DAYTONA_X, BIOS RYM0081C 07/13/2020
 Call Trace:
  dump_stack+0xa5/0xe6
  print_address_description.constprop.0+0x18/0x130
  ? kvm_make_vcpus_request_mask+0x174/0x440 [kvm]
  __kasan_report.cold+0x7f/0x114
  ? kvm_make_vcpus_request_mask+0x174/0x440 [kvm]
  kasan_report+0x38/0x50
  kasan_check_range+0xf5/0x1d0
  kvm_make_vcpus_request_mask+0x174/0x440 [kvm]
  kvm_make_scan_ioapic_request_mask+0x84/0xc0 [kvm]
  ? kvm_arch_exit+0x110/0x110 [kvm]
  ? sched_clock+0x5/0x10
  ioapic_write_indirect+0x59f/0x9e0 [kvm]
  ? static_obj+0xc0/0xc0
  ? __lock_acquired+0x1d2/0x8c0
  ? kvm_ioapic_eoi_inject_work+0x120/0x120 [kvm]

The problem appears to be that 'vcpu_bitmap' is allocated as a single long
on stack and it should really be KVM_MAX_VCPUS long. We also seem to clear
the lower 16 bits of it with bitmap_zero() for no particular reason (my
guess would be that 'bitmap' and 'vcpu_bitmap' variables in
kvm_bitmap_or_dest_vcpus() caused the confusion: while the later is indeed
16-bit long, the later should accommodate all possible vCPUs).

Fixes: 7ee30bc132c6 ("KVM: x86: deliver KVM IOAPIC scan request to target vCPUs")
Fixes: 9a2ae9f6b6bb ("KVM: x86: Zero the IOAPIC scan request dest vCPUs bitmap")
Reported-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210827092516.1027264-7-vkuznets@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index ff005fe738a4c1dae5e2b6b4648e1d5f34cfd24c..8c065da73f8e541430770fd860653e4dee4a470c 100644 (file)
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -319,8 +319,8 @@ static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val)
        unsigned index;
        bool mask_before, mask_after;
        union kvm_ioapic_redirect_entry *e;
-       unsigned long vcpu_bitmap;
        int old_remote_irr, old_delivery_status, old_dest_id, old_dest_mode;
+       DECLARE_BITMAP(vcpu_bitmap, KVM_MAX_VCPUS);
 
        switch (ioapic->ioregsel) {
        case IOAPIC_REG_VERSION:
@@ -384,9 +384,9 @@ static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val)
                        irq.shorthand = APIC_DEST_NOSHORT;
                        irq.dest_id = e->fields.dest_id;
                        irq.msi_redir_hint = false;
-                       bitmap_zero(&vcpu_bitmap, 16);
+                       bitmap_zero(vcpu_bitmap, KVM_MAX_VCPUS);
                        kvm_bitmap_or_dest_vcpus(ioapic->kvm, &irq,
-                                                &vcpu_bitmap);
+                                                vcpu_bitmap);
                        if (old_dest_mode != e->fields.dest_mode ||
                            old_dest_id != e->fields.dest_id) {
                                /*
@@ -399,10 +399,10 @@ static void ioapic_write_indirect(struct kvm_ioapic *ioapic, u32 val)
                                    kvm_lapic_irq_dest_mode(
                                        !!e->fields.dest_mode);
                                kvm_bitmap_or_dest_vcpus(ioapic->kvm, &irq,
-                                                        &vcpu_bitmap);
+                                                        vcpu_bitmap);
                        }
                        kvm_make_scan_ioapic_request_mask(ioapic->kvm,
-                                                         &vcpu_bitmap);
+                                                         vcpu_bitmap);
                } else {
                        kvm_make_scan_ioapic_request(ioapic->kvm);
                }