SGX ioctl() calls are serialized with a lock. It's a weird open-coded lock that is not even called a "lock". That makes it a weird beast, but Sean has convinced me it's a good idea without better alternatives.
Give the lock bit a better name, and document what it actually trying to do. Cc: Sean Christopherson <[email protected]> Cc: Jarkko Sakkinen <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: [email protected] --- b/arch/x86/kernel/cpu/sgx/encl.h | 2 +- b/arch/x86/kernel/cpu/sgx/ioctl.c | 19 ++++++++++++++++--- 2 files changed, 17 insertions(+), 4 deletions(-) diff -puN arch/x86/kernel/cpu/sgx/ioctl.c~sgx-encl-flags arch/x86/kernel/cpu/sgx/ioctl.c --- a/arch/x86/kernel/cpu/sgx/ioctl.c~sgx-encl-flags 2021-01-12 14:02:24.480689006 -0800 +++ b/arch/x86/kernel/cpu/sgx/ioctl.c 2021-01-12 14:02:24.486689006 -0800 @@ -690,8 +690,21 @@ long sgx_ioctl(struct file *filep, unsig struct sgx_encl *encl = filep->private_data; int ret; - if (test_and_set_bit(SGX_ENCL_IOCTL, &encl->flags)) - return -EBUSY; + /* + * Behold, the Big SGX Lock + * + * The primary function of this "lock" is to actively discourage + * attempts at multi-threaded enclave management. Enclave management + * is fundamentally a single-threaded affair. Enclave measurement, + * for instance would be worthless if two ADD_PAGES instances raced + * and occurred in different orders. + * + * encl->lock is ill suited for this because it would need to be + * conditionally dropped and reqacuired for operations like enclave + * page allocation and reclaim. + */ + if (test_and_set_bit(SGX_ENCL_IOCTL_LOCK, &encl->flags)) + return -EINVAL; switch (cmd) { case SGX_IOC_ENCLAVE_CREATE: @@ -711,6 +724,6 @@ long sgx_ioctl(struct file *filep, unsig break; } - clear_bit(SGX_ENCL_IOCTL, &encl->flags); + clear_bit(SGX_ENCL_IOCTL_LOCK, &encl->flags); return ret; } diff -puN arch/x86/kernel/cpu/sgx/encl.h~sgx-encl-flags arch/x86/kernel/cpu/sgx/encl.h --- a/arch/x86/kernel/cpu/sgx/encl.h~sgx-encl-flags 2021-01-12 14:02:24.482689006 -0800 +++ b/arch/x86/kernel/cpu/sgx/encl.h 2021-01-12 14:16:37.511686879 -0800 @@ -34,7 +34,7 @@ struct sgx_encl_page { }; enum sgx_encl_flags { - SGX_ENCL_IOCTL = BIT(0), + SGX_ENCL_IOCTL_LOCK = BIT(0), /* See sgx_ioctl() */ SGX_ENCL_DEBUG = BIT(1), SGX_ENCL_CREATED = BIT(2), SGX_ENCL_INITIALIZED = BIT(3), _
