kvm: don't take vcpu mutex for obviously invalid vcpu ioctls

commit 2ea75be3219571d0ec009ce20d9971e54af96e09 upstream.

vcpu ioctls can hang the calling thread if issued while a vcpu is running.
However, invalid ioctls can happen when userspace tries to probe the kind
of file descriptors (e.g. isatty() calls ioctl(TCGETS)); in that case,
we know the ioctl is going to be rejected as invalid anyway and we can
fail before trying to take the vcpu mutex.

This patch does not change functionality, it just makes invalid ioctls
fail faster.

Signed-off-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 41efe4b9ca919b28bad5ae030c289de7e76a9fc1..6a3f29bd43d7a166c2b1504f00fcefae36ed0924 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -52,6 +52,7 @@
 
 #include <asm/processor.h>
 #include <asm/io.h>
+#include <asm/ioctl.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
 
@@ -1991,6 +1992,9 @@ static long kvm_vcpu_ioctl(struct file *filp,
        if (vcpu->kvm->mm != current->mm)
                return -EIO;
 
+       if (unlikely(_IOC_TYPE(ioctl) != KVMIO))
+               return -EINVAL;
+
 #if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS)
        /*
         * Special cases: vcpu ioctls that are asynchronous to vcpu execution,