On Tue, Sep 04, 2018 at 09:35:46AM -0700, Sean Christopherson wrote: > On Tue, Sep 04, 2018 at 06:30:21PM +0300, Jarkko Sakkinen wrote: > > On Tue, Sep 04, 2018 at 07:54:51AM -0700, Sean Christopherson wrote: > > > I don't see any value in trying to rule out specific causes of > > > INVALID_TOKEN, but we should only retry EINIT if ret==INVALID_TOKEN > > > and RDMSR(HASH0) != sgx_lepubkeyhash[0]. Only the first MSR needs to > > > be checked for validity as they're a package deal, i.e. they'll all be > > > valid or all be reset. There shouldn't be a limit on retry attempts, > > > e.g. the MSRs could theoretically be reset between WRMSR and EINIT. > > > > Why is doing rdmsrs necessary? With the INVALID_TOKEN error we know we > > are out-of-sync i.e. have been sleeping and then one just needs to do > > wrmsrs. > > As Kai mentioned, INVALID_TOKEN is returned for other reasons, e.g. a > production enclave trying to use a debug token or reserved bits set in > the token. And in the KVM case, the hash and token are provided by > the guest, so it's entirely possible the enclave/token is not signed > with the key specified in the hash. RDMSR is relatively inexpensive > compared to the overall cost of EINIT. Though of course EINIT failure > isn't exactly a fast path, so I'm ok if you want to opt for simplicity > and retry on INVALID_TOKEN without checking the MSRs, just make sure > to add a comment indicating we're intentionally not checking the MSRs. Great! > > I think one retry should be enough given that VMM traps EINIT. One retry > > is needed to take care of the guest itself (or host if we are running on > > bare metal) having been in a sleep state. > > Assuming we do RDMSR(hash0), that should be sufficient to prevent > infinite retry and it protects against the MSRs being lost between > WRMSR and EINIT during retry. That being said, I'm ok retrying only > once, especially if you want to omit the RDMSR. Disabling preemption > should prevent the kernel from suspending between WRMSR and EINIT, > I'm just being paranoid. But they are in the same preempt-disabled-region already? /Jarkko
