Reported by syzkaller:
WARNING: CPU: 0 PID: 27962 at arch/x86/kvm/emulate.c:5631
x86_emulate_insn+0x557/0x15f0 [kvm]
Modules linked in: kvm_intel kvm [last unloaded: kvm]
CPU: 0 PID: 27962 Comm: syz-executor Tainted: G B W
4.15.0-rc2-next-20171208+ #32
Hardware name: Intel Corporation S1200SP/S1200SP, BIOS
S1200SP.86B.01.03.0006.040720161253 04/07/2016
RIP: 0010:x86_emulate_insn+0x557/0x15f0 [kvm]
RSP: 0018:ffff8807234476d0 EFLAGS: 00010282
RAX: 0000000000000000 RBX: ffff88072d0237a0 RCX: ffffffffa0065c4d
RDX: 1ffff100e5a046f9 RSI: 0000000000000003 RDI: ffff88072d0237c8
RBP: ffff880723447728 R08: ffff88072d020000 R09: ffffffffa008d240
R10: 0000000000000002 R11: ffffed00e7d87db3 R12: ffff88072d0237c8
R13: ffff88072d023870 R14: ffff88072d0238c2 R15: ffffffffa008d080
FS: 00007f8a68666700(0000) GS:ffff880802200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000002009506c CR3: 000000071fec4005 CR4: 00000000003626f0
Call Trace:
x86_emulate_instruction+0x3bc/0xb70 [kvm]
? reexecute_instruction.part.162+0x130/0x130 [kvm]
vmx_handle_exit+0x46d/0x14f0 [kvm_intel]
? trace_event_raw_event_kvm_entry+0xe7/0x150 [kvm]
? handle_vmfunc+0x2f0/0x2f0 [kvm_intel]
? wait_lapic_expire+0x25/0x270 [kvm]
vcpu_enter_guest+0x720/0x1ef0 [kvm]
...
When cs.l is set, vcpu should run in the 64 bit paging mode.
Current kvm set_sregs function doesn't have such check when userspace
inputs sreg values. This will lead unexpected behavior. This patch
is to add such check.
Suggested-by: Paolo Bonzini <pbonz...@redhat.com>
Reported-by: Dmitry Vyukov <dvyu...@google.com>
Cc: Paolo Bonzini <pbonz...@redhat.com>
Cc: Radim Krčmář <rkrc...@redhat.com>
Cc: Dmitry Vyukov <dvyu...@google.com>
Cc: Jim Mattson <jmatt...@google.com>
Signed-off-by: Tianyu Lan <tianyu....@intel.com>
Signed-off-by: Lan Tianyu <tianyu....@intel.com>
---
arch/x86/kvm/x86.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1e1e617..07d6d6c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7485,6 +7485,18 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16
tss_selector, int idt_index,
}
EXPORT_SYMBOL_GPL(kvm_task_switch);
+int kvm_valid_sregs(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs)
+{
+ /* When cs.l is set, vcpu should run in 64-bit mode */
+ if (sregs->cs.l)
+ if (!((sregs->cr0 & X86_CR0_PG_BIT) &&
+ (sregs->cr4 & X86_CR4_PAE_BIT) &&
+ (sregs->efer & EFER_LME)))
+ return -EINVAL;
+
+ return 0;
+}
+
int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
struct kvm_sregs *sregs)
{
@@ -7497,6 +7509,9 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
(sregs->cr4 & X86_CR4_OSXSAVE))
return -EINVAL;
+ if (kvm_valid_sregs(vcpu, sregs))
+ return -EINVAL;
+
apic_base_msr.data = sregs->apic_base;
apic_base_msr.host_initiated = true;
if (kvm_set_apic_base(vcpu, &apic_base_msr))
--
1.8.3.1
