From 9cb09e7c1c9af2968d5186ef9085f05641ab65d9 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Thu, 14 Nov 2019 13:17:39 +0000 Subject: [PATCH] KVM: Add a comment describing the /dev/kvm no_compat handling Add a comment explaining the rational behind having both no_compat open and ioctl callbacks to fend off compat tasks. Signed-off-by: Marc Zyngier Signed-off-by: Paolo Bonzini --- virt/kvm/kvm_main.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 6a65ed915c7a..13efc291b1c7 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -122,6 +122,13 @@ static long kvm_vcpu_compat_ioctl(struct file *file, unsigned int ioctl, unsigned long arg); #define KVM_COMPAT(c) .compat_ioctl = (c) #else +/* + * For architectures that don't implement a compat infrastructure, + * adopt a double line of defense: + * - Prevent a compat task from opening /dev/kvm + * - If the open has been done by a 64bit task, and the KVM fd + * passed to a compat task, let the ioctls fail. + */ static long kvm_no_compat_ioctl(struct file *file, unsigned int ioctl, unsigned long arg) { return -EINVAL; }