[PATCH 5.10 17/93] KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect()

Greg Kroah-Hartman
2021-10-04T13:20:09Z

From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit 2f9b68f57c6278c322793a06063181deded0ad69 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/ioapic.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)

--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -319,8 +319,8 @@ static void ioapic_write_indirect(struct
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
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_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);
}