From: David Matlack <dmatlack@google.com>
Date: Fri, 19 Sep 2014 23:03:25 +0000 (-0700)
Subject: kvm: don't take vcpu mutex for obviously invalid vcpu ioctls
X-Git-Tag: v3.2.65~138
X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?p=pandora-kernel.git;a=commitdiff_plain;h=f9b5299d5ae1ba735fa3cc081fd5dc0dc33ba2e8;hp=0e251ad92556811f83ce7c2455b05ec1dcb44d71

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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index d83aa5e700d5..8b0617a648d1 100644
--- 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>
 
@@ -1766,6 +1767,9 @@ 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)
 	/*
 	 * Special cases: vcpu ioctls that are asynchronous to vcpu execution,