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KVM: Protect vcpu->pid dereference via debugfs with RCU

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Wrap the vcpu->pid dereference in the debugfs hook vcpu_get_pid() with
proper RCU read (un)lock.  Unlike the code in kvm_vcpu_ioctl(),
vcpu_get_pid() is not a simple access; the pid pointer is passed to
pid_nr() and fully dereferenced if the pointer is non-NULL.

Failure to acquire RCU could result in use-after-free of the old pid if
a different task invokes KVM_RUN and puts the last reference to the old
vcpu->pid between vcpu_get_pid() reading the pointer and dereferencing it
in pid_nr().

Fixes: e36de87d34 ("KVM: debugfs: expose pid of vcpu threads")
Link: https://lore.kernel.org/r/20230211010719.982919-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2023-02-11 01:07:19 +00:00
parent b9846a698c
commit 76021e96d7
1 changed files with 4 additions and 1 deletions
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5
virt/kvm/kvm_main.c
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@ -3870,7 +3870,10 @@ static int create_vcpu_fd(struct kvm_vcpu *vcpu)
static int vcpu_get_pid(void *data, u64 *val)
{
struct kvm_vcpu *vcpu = data;
*val = pid_nr(rcu_access_pointer(vcpu->pid));
rcu_read_lock();
*val = pid_nr(rcu_dereference(vcpu->pid));
rcu_read_unlock();
return 0;
}