Re: [PATCH v3 4/4] KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect()

[Sean Christopherson <seanjc@google.com>]

On Thu, Aug 26, 2021, Vitaly Kuznetsov wrote:
> 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>