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Diffstat (limited to 'Documentation/x86/sgx.rst')
| -rw-r--r-- | Documentation/x86/sgx.rst | 41 |
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diff --git a/Documentation/x86/sgx.rst b/Documentation/x86/sgx.rst index eaee1368b4fd..dd0ac96ff9ef 100644 --- a/Documentation/x86/sgx.rst +++ b/Documentation/x86/sgx.rst @@ -209,3 +209,44 @@ An application may be loaded into a container enclave which is specially configured with a library OS and run-time which permits the application to run. The enclave run-time and library OS work together to execute the application when a thread enters the enclave. + +Impact of Potential Kernel SGX Bugs +=================================== + +EPC leaks +--------- + +When EPC page leaks happen, a WARNING like this is shown in dmesg: + +"EREMOVE returned ... and an EPC page was leaked. SGX may become unusable..." + +This is effectively a kernel use-after-free of an EPC page, and due +to the way SGX works, the bug is detected at freeing. Rather than +adding the page back to the pool of available EPC pages, the kernel +intentionally leaks the page to avoid additional errors in the future. + +When this happens, the kernel will likely soon leak more EPC pages, and +SGX will likely become unusable because the memory available to SGX is +limited. However, while this may be fatal to SGX, the rest of the kernel +is unlikely to be impacted and should continue to work. + +As a result, when this happpens, user should stop running any new +SGX workloads, (or just any new workloads), and migrate all valuable +workloads. Although a machine reboot can recover all EPC memory, the bug +should be reported to Linux developers. + + +Virtual EPC +=========== + +The implementation has also a virtual EPC driver to support SGX enclaves +in guests. Unlike the SGX driver, an EPC page allocated by the virtual +EPC driver doesn't have a specific enclave associated with it. This is +because KVM doesn't track how a guest uses EPC pages. + +As a result, the SGX core page reclaimer doesn't support reclaiming EPC +pages allocated to KVM guests through the virtual EPC driver. If the +user wants to deploy SGX applications both on the host and in guests +on the same machine, the user should reserve enough EPC (by taking out +total virtual EPC size of all SGX VMs from the physical EPC size) for +host SGX applications so they can run with acceptable performance. |