Document the Software Guard eXtensions kernel features, which were available in Linux v5.11. Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxxx> --- v12: * Fix issues reported by Alejandro. * Expand the explanation and make the text a bit more consistent. * SGX_IOC_ENCLAVE_PROVISION was missing. v11: * Address Reinette's remarks for v10: https://lore.kernel.org/linux-sgx/8f84b8e8-b478-bb81-4aa8-536df882a144@xxxxxxxxx/ v10: * v9 was malformed, essentially a resend. v9: * Rename "Address Space" section as "Memory mapping", and refine the text. * Rename "Ioctls" section as "Construction", and refine the text. v8: * Fix errors reported for the previous version. v7: * Added more meat about the address space and API. * Reorganized the text to have focus more on developer to have a big picture of kernel provided interfaces. v6: * Small fixes based on Dave's and Reinette's feedback. * Extended the "Permissions" section to cover mmap() v5: * Taking away hardware concepts and focusing more on the interface. v4: * Did a heavy edit trying to streamline the story a bit and focus on stuff important to the user (e.g. lighten up x86 details). v3: * Overhaul based on Michael's comments. Most likely needs to be refined in various places but this is at least a small step forward for sure. v2: * Fixed the semantic newlines convention and various style errors etc. that were reported by Alenjandro and Michael. * SGX was merged to v5. --- man7/sgx.7 | 164 ++++++++++++++++++++++++++++++++++++++++++++++++++++ man7/vdso.7 | 1 + 2 files changed, 165 insertions(+) create mode 100644 man7/sgx.7 diff --git a/man7/sgx.7 b/man7/sgx.7 new file mode 100644 index 000000000..20d2d4777 --- /dev/null +++ b/man7/sgx.7 @@ -0,0 +1,164 @@ +.\" Copyright (C) 2021 Intel Corporation +.\" +.\" %%%LICENSE_START(VERBATIM) +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and authors of this work. +.\" %%%LICENSE_END +.\" +.TH SGX 7 2021\-02\-02 "Linux" "Linux Programmer's Manual" +.PP +sgx - overview of Software Guard eXtensions +.SH SYNOPSIS +.nf +.B #include <asm/sgx.h> +.PP +.IB enclave " = open(" \(dq/dev/sgx_enclave\(dq ", O_RDWR);" +.fi +.SH DESCRIPTION +Intel Software Guard eXtensions (SGX) allow applications to host +enclaves, +protected executable objects in encrypted memory. +.PP +Enclaves are blobs of executable code, +running inside a CPU enforced container, +which is mapped to the process address space. +They are represented as the open files of +.IR /dev/sgx_enclave . +Enclaves can have an arbitrary fixed set of entry points, +entered with the leaf functions of ENCLU x86 opcode. +Once entered, +CPU executes inside the enclave and can access its memory. +Exceptions, +some x86 opcodes, +and privilege level changes will throw the CPU out of the enclave, +and they must be handled by the host. +.PP +SGX can only be available if the kernel is configured and built with the +.B CONFIG_X86_SGX +option. +If CPU, BIOS and kernel have SGX enabled, +.I sgx +appears in the +.I flags +field of +.IR /proc/cpuinfo . +.PP +If SGX appears not to be available, +ensure that SGX is enabled in the BIOS. +If a BIOS presents a choice between +.I Enabled +and +.I Software Enabled +modes for SGX, +choose +.IR Enabled . +.SS Memory mapping +The file descriptor of an enclave can be shared among multiple processes. +An enclave is required by the CPU to be placed to an address, +which is a multiple of its size. +An address range containing a reasonable base address can be probed with an anonymous +.BR mmap(2) +call: +.PP +.in +4 +.EX +void *area = mmap(NULL, size * 2, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, + -1, 0); + +void *base = ((uintptr_t) area + size - 1) & ~(size - 1); +.EE +.in +.PP +The enclave file descriptor itself can be then mapped with the +.B MAP_FIXED +flag set to the carved out memory. +.SS Entering the enclave +Kernel defines +.IR __vdso_sgx_enter_enclave +.BR vdso (7) +for entering to the enclave. +Further, the prototype for the +.BR vdso (7) +is defined by +.I vdso_sgx_enter_enclave_t +in +.IR <asm/sgx.h> . +.IR __vdso_sgx_enter_enclave +wraps the logic for entering the enclave, +and provides kernel assisted CPU exception handling. +CPU exceptions are returned back to the host, +which can then handle the situation in-behalf of the enclave. +.SS Permissions +.PP +During the build process each enclave page is assigned permissions, +as part of +.I SGX_IOC_ENCLAVE_ADD_PAGES . +These are the maximum permissions with which the page can be be mapped. +If +.BR mmap (2) +is called with higher permissions than those defined during the build, +it will return +.B -EACCES . +If +.I SGX_IOC_ENCLAVE_ADD_PAGES +is called after +.BR mmap (2) +with lower permissions, +the caller receives +.BR SIGBUS , +once it accesses the page for the first time. +.SS Ioctls +Enclaves are managed with the +.BR ioctl (2) +interface in +.IR <asm/sgx.h> : +.TP +.B SGX_IOC_ENCLAVE_CREATE +Create SGX Enclave Control Structure (SECS) for the enclave. +SECS is a hardware defined structure, +which contains the global properties of an enclave. +.B SGX_IOC_ENCLAVE_CREATE +is a one-shot call that fixes the enclave's address and +size for the rest of its life-cycle. +.TP +.B SGX_IOC_ENCLAVE_ADD_PAGES +Fill a range of the enclave's pages with the caller provided data and permissions. +The pages added are either regular pages for code and data, +or thread control structures (TCS). +The latter define the entry points to the enclave, +which can be entered after the initialization. +.TP +.B SGX_IOC_ENCLAVE_INIT +Initialize the enclave for the run-time. +After a successful initialization, +no new pages can be added to the enclave. +.B SGX_IOC_ENCLAVE_PROVISION +Allow an enclave the enclave access the provision key, +required for remote attestation. +A file handle to +.IR /dev/sgx_provision +must be supplied in order to grant the permission. +.SH VERSIONS +The SGX feature was added in Linux 5.11. +.SH SEE ALSO +.BR ioctl (2), +.BR mmap (2), +.BR mprotect (2) +.BR vdso (7) diff --git a/man7/vdso.7 b/man7/vdso.7 index 9b426f823..d231c96cc 100644 --- a/man7/vdso.7 +++ b/man7/vdso.7 @@ -548,6 +548,7 @@ __vdso_clock_gettime LINUX_2.6 __vdso_getcpu LINUX_2.6 __vdso_gettimeofday LINUX_2.6 __vdso_time LINUX_2.6 +__vdso_sgx_enter_enclave LINUX5.11 .TE .if t \{\ .in -- 2.35.1
