SGX currently allows EPC pages to be overcommitted. If the system is out of enclave memory, EPC pages are swapped to normal RAM via a per enclave shared memory area. This shared memory is not charged to the enclave or the task mapping it, making it hard to account for using normal methods. Since SGX will allow EPC pages to be overcommitted without limits, enclaves can consume system memory for these backing pages without limits. In order to prevent this, set a cap on the amount of overcommit SGX allows based on a module param which can be set at boot time. Then, whenever a backing page is requested by an enclave, keep track of the total amount of shared memory pages used across all enclaves and return an error if the overcommit limit has been reached. This will restrict the total amount of backing pages that all enclaves can consume to a maximum amount, and prevent enclaves from consuming all the system RAM for backing pages. The overcommit percentage has a default value of 100, which limits shared memory page consumption to equal to the number of EPC pages in the system. If sgx.overcommit_percent is set to a negative value, SGX will not place any limits on the amount of overcommit that might be requested, and SGX will behave as it has previously without the sgx.overcommit_percent limit. Kristen Carlson Accardi (2): x86/sgx: Add accounting for tracking overcommit x86/sgx: account backing pages .../admin-guide/kernel-parameters.txt | 7 ++ Documentation/x86/sgx.rst | 16 +++- arch/x86/kernel/cpu/sgx/Makefile | 6 +- arch/x86/kernel/cpu/sgx/encl.c | 76 ++++++++++++++++++- arch/x86/kernel/cpu/sgx/encl.h | 6 +- arch/x86/kernel/cpu/sgx/main.c | 70 ++++++++++++++++- arch/x86/kernel/cpu/sgx/sgx.h | 2 + 7 files changed, 173 insertions(+), 10 deletions(-) -- 2.20.1
