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KVM: Add a comment describing the /dev/kvm no_compat handling

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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 <maz@kernel.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Marc Zyngier 2019-11-14 13:17:39 +00:00 committed by Paolo Bonzini
parent ed69a6cb70
commit 9cb09e7c1c
1 changed files with 7 additions and 0 deletions
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7
virt/kvm/kvm_main.c
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@ -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; }