From: Wanpeng Li wanpeng.li@hotmail.com
[ Upstream commit c37c28730bb031cc8a44a130c2555c0f3efbe2d0 ]
Reported by syzkaller:
*** Guest State *** CR0: actual=0x0000000080010031, shadow=0x0000000060000010, gh_mask=fffffffffffffff7 CR4: actual=0x0000000000002061, shadow=0x0000000000000000, gh_mask=ffffffffffffe8f1 CR3 = 0x000000002081e000 RSP = 0x000000000000fffa RIP = 0x0000000000000000 RFLAGS=0x00023000 DR7 = 0x00000000000000 ^^^^^^^^^^ ------------[ cut here ]------------ WARNING: CPU: 6 PID: 24431 at /home/kernel/linux/arch/x86/kvm//x86.c:7302 kvm_arch_vcpu_ioctl_run+0x651/0x2ea0 [kvm] CPU: 6 PID: 24431 Comm: reprotest Tainted: G W OE 4.14.0+ #26 RIP: 0010:kvm_arch_vcpu_ioctl_run+0x651/0x2ea0 [kvm] RSP: 0018:ffff880291d179e0 EFLAGS: 00010202 Call Trace: kvm_vcpu_ioctl+0x479/0x880 [kvm] do_vfs_ioctl+0x142/0x9a0 SyS_ioctl+0x74/0x80 entry_SYSCALL_64_fastpath+0x23/0x9a
The failed vmentry is triggered by the following beautified testcase:
#include <unistd.h> #include <sys/syscall.h> #include <string.h> #include <stdint.h> #include <linux/kvm.h> #include <fcntl.h> #include <sys/ioctl.h>
long r[5]; int main() { struct kvm_debugregs dr = { 0 };
r[2] = open("/dev/kvm", O_RDONLY); r[3] = ioctl(r[2], KVM_CREATE_VM, 0); r[4] = ioctl(r[3], KVM_CREATE_VCPU, 7); struct kvm_guest_debug debug = { .control = 0xf0403, .arch = { .debugreg[6] = 0x2, .debugreg[7] = 0x2 } }; ioctl(r[4], KVM_SET_GUEST_DEBUG, &debug); ioctl(r[4], KVM_RUN, 0); }
which testcase tries to setup the processor specific debug registers and configure vCPU for handling guest debug events through KVM_SET_GUEST_DEBUG. The KVM_SET_GUEST_DEBUG ioctl will get and set rflags in order to set TF bit if single step is needed. All regs' caches are reset to avail and GUEST_RFLAGS vmcs field is reset to 0x2 during vCPU reset. However, the cache of rflags is not reset during vCPU reset. The function vmx_get_rflags() returns an unreset rflags cache value since the cache is marked avail, it is 0 after boot. Vmentry fails if the rflags reserved bit 1 is 0.
This patch fixes it by resetting both the GUEST_RFLAGS vmcs field and its cache to 0x2 during vCPU reset.
Reported-by: Dmitry Vyukov dvyukov@google.com Tested-by: Dmitry Vyukov dvyukov@google.com Reviewed-by: David Hildenbrand david@redhat.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Radim Krčmář rkrcmar@redhat.com Cc: Nadav Amit nadav.amit@gmail.com Cc: Dmitry Vyukov dvyukov@google.com Signed-off-by: Wanpeng Li wanpeng.li@hotmail.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- arch/x86/kvm/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index fedb5c2962f2..9b02ba40fed0 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -4569,7 +4569,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu) vmcs_writel(GUEST_SYSENTER_ESP, 0); vmcs_writel(GUEST_SYSENTER_EIP, 0);
- vmcs_writel(GUEST_RFLAGS, 0x02); + kvm_set_rflags(vcpu, X86_EFLAGS_FIXED); kvm_rip_write(vcpu, 0xfff0);
vmcs_writel(GUEST_GDTR_BASE, 0);