Messages in this thread | | | From | Jann Horn <> | Date | Mon, 3 Sep 2018 15:53:24 +0200 | Subject | Re: [PATCH v13 10/13] x86/sgx: Add sgx_einit() for initializing enclaves |
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On Mon, Sep 3, 2018 at 3:33 PM Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> wrote: > > From: Sean Christopherson <sean.j.christopherson@intel.com> > > Add a function to perform ENCLS(EINIT), which initializes an enclave, > which can be used by a driver for running enclaves and VMMs. > > Writing the LE hash MSRs is extraordinarily expensive, e.g. 3-4x slower > than normal MSRs, so we use a per-cpu cache to track the last known value > of the MSRs to avoid unnecessarily writing the MSRs with the current value. > > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> > Co-developed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> [...] > +/** > + * sgx_einit - initialize an enclave > + * @sigstruct: a pointer to the SIGSTRUCT > + * @token: a pointer to the EINITTOKEN > + * @secs_page: a pointer to the SECS EPC page > + * @lepubkeyhash: the desired value for IA32_SGXLEPUBKEYHASHx MSRs > + * > + * Try to perform EINIT operation. If the MSRs are writable, they are updated > + * according to @lepubkeyhash. > + * > + * Return: > + * 0 on success, > + * -errno on failure > + * SGX error code if EINIT fails > + */ > +int sgx_einit(struct sgx_sigstruct *sigstruct, struct sgx_einittoken *token, > + struct sgx_epc_page *secs_page, u64 lepubkeyhash[4]) > +{ > + struct sgx_lepubkeyhash __percpu *cache; > + bool cache_valid; > + int i, ret; > + > + if (!sgx_lc_enabled) > + return __einit(sigstruct, token, sgx_epc_addr(secs_page)); > + > + cache = per_cpu(sgx_lepubkeyhash_cache, smp_processor_id());
At this point, preemption must be off, because smp_processor_id() is called; I don't think it is off here? If you have hardware/emulation on which you can test this, you may want to test your patches with DEBUG_PREEMPT enabled.
> + if (!cache) { > + cache = kzalloc(sizeof(struct sgx_lepubkeyhash), GFP_KERNEL);
But then here you do a GFP_KERNEL allocation, which can sleep.
Also: After "cache" has been allocated in this branch, when do you store the reference to it? As far as I can tell, you never write to sgx_lepubkeyhash_cache, and the allocation just leaks.
> + if (!cache) > + return -ENOMEM; > + } > + > + cache_valid = cache->pm_cnt == sgx_pm_cnt;
The cache should probably not be treated as valid if it has just been created and only contains zeroes, right?
> + cache->pm_cnt = sgx_pm_cnt;
Can sgx_pm_cnt be modified concurrently? If so, please use at least READ_ONCE() to document that and prevent the compiler from doing weird stuff.
> + preempt_disable();
And here you turn off preemption, but it should already have been off?
> + for (i = 0; i < 4; i++) { > + if (cache_valid && lepubkeyhash[i] == cache->msrs[i]) > + continue; > + > + wrmsrl(MSR_IA32_SGXLEPUBKEYHASH0 + i, lepubkeyhash[i]); > + cache->msrs[i] = lepubkeyhash[i]; > + } > + ret = __einit(sigstruct, token, sgx_epc_addr(secs_page)); > + preempt_enable(); > + return ret; > +} > +EXPORT_SYMBOL(sgx_einit); > +
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