linux-kernel - [PATCH 4.9 06/23] KVM: PPC: Fix oops when checking KVM_CAP_PPC

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Date:   Tue, 31 Oct 2017 10:55:30 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Greg Kurz <groug@...d.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Thomas Huth <thuth@...hat.com>,
        Paul Mackerras <paulus@...abs.org>
Subject: [PATCH 4.9 06/23] KVM: PPC: Fix oops when checking KVM_CAP_PPC_HTM

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Greg Kurz <groug@...d.org>

commit ac64115a66c18c01745bbd3c47a36b124e5fd8c0 upstream.

The following program causes a kernel oops:

#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/kvm.h>

main()
{
    int fd = open("/dev/kvm", O_RDWR);
    ioctl(fd, KVM_CHECK_EXTENSION, KVM_CAP_PPC_HTM);
}

This happens because when using the global KVM fd with
KVM_CHECK_EXTENSION, kvm_vm_ioctl_check_extension() gets
called with a NULL kvm argument, which gets dereferenced
in is_kvmppc_hv_enabled(). Spotted while reading the code.

Let's use the hv_enabled fallback variable, like everywhere
else in this function.

Fixes: 23528bb21ee2 ("KVM: PPC: Introduce KVM_CAP_PPC_HTM")
Signed-off-by: Greg Kurz <groug@...d.org>
Reviewed-by: David Gibson <david@...son.dropbear.id.au>
Reviewed-by: Thomas Huth <thuth@...hat.com>
Signed-off-by: Paul Mackerras <paulus@...abs.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/powerpc/kvm/powerpc.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -601,8 +601,7 @@ int kvm_vm_ioctl_check_extension(struct
 		break;
 #endif
 	case KVM_CAP_PPC_HTM:
-		r = cpu_has_feature(CPU_FTR_TM_COMP) &&
-		    is_kvmppc_hv_enabled(kvm);
+		r = cpu_has_feature(CPU_FTR_TM_COMP) && hv_enabled;
 		break;
 	default:
 		r = 0;