sgx.7: New page with overview of Software Guard eXtensions (SGX)
Jarkko Sakkinen
maintainerPATCH v7 1/1 sgx.7: New page with overview of Software Guard eXtensions (SGX)
---
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 | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 156 insertions(+) create mode 100644 man7/sgx.7
man7/sgx.7 new file +156 -0
@@ -0,0 +1,156 @@ +.\" 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 +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date.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 +.EX +.B #include <asm/sgx.h> +.PP +.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);" +.EE +.SH DESCRIPTION +Intel Software Guard eXtensions (SGX) allow applications to host, +enclaves, +protected executable objects in memory. +As software entities enclaves are instances of +.I /dev/sgx_enclave. +.PP +SGX can be available only if the kernel was configured and built with the +.B CONFIG_X86_SGX +option. +You can verify that both the kernel and hardware have SGX enabled by +checking that "sgx" appears in the +.I flags +field in +.IR /proc/cpuinfo . +.PP +SGX must be enabled in BIOS. +If SGX appears to be unsupported, +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 +.I Enabled. +.PP +Enclaves are shared objects, meaning that +they can be shared with a +.BR cmsg (3), +and inherited in a fork. +.SS Address space +The address range for an enclave must be reserved with +.BR mmap (2). +This must happen before the enclave construction can begin, +because the enclave page addresses are fixed during its build time. +.PP +The CPU requires the size of the enclave to be power of two, +and the base address to be naturally aligned with the size. +An appropriate address range can be found by an anonymous mapping: +.PP +.EX +void *area = mmap(NULL, size * 2, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, + -1, 0); + +/* Find the first address aligned to the size within the range. */ +void *base = ((uint64_t)area + size - 1) & ~(size - 1); +.EE +.PP +.SS Ioctls +Enclaves are managed with the +.BR ioctl (2) +interface defined and documented in +.IR <asm/sgx.h>: +.TP +.IB SGX_IOC_ENCLAVE_CREATE +Create SGX Enclave Control Structure (SECS) for an enclave. +SECS is a hardware defined structure, +which contains the properties of an enclave, +such as its base address and size. +.TP +.IB SGX_IOC_ENCLAVE_ADD_PAGES +Populate a range of enclave pages with the page data provided by the caller. +.TP +.IB SGX_IOC_ENCLAVE_INIT +Tell the CPU the prepare the enclave for use. +After a successful initialization, +no new pages can be added to the enclave. +.PP +The details of what these operations actually mean in the hardware level can be +found in the Intel Software Developers Manual. +.SS vDSO +A process can access enclave by entering into its address space through +a set of entry points, +which must be defined during the construction process. +This requires a complex sequence of CPU instructions, +and kernel assisted exception handling. +For these reasons, +it is encapsulated into +vDSO interface, +provided by +.BR vdso_sgx_enter_enclave_t, +which is located in +.IR <asm/sgx.h>. +.SS Permissions +In order to build an enclave, a process must be able to call +.IR mmap (2) +with +.IR PROT_EXEC +set, +because like for any other type of executable, +the page table permissions must be set appropriately. +Therefore, +.I /dev/sgx_enclave +must reside in a partition, +which is not mounted with +.B noexec +set in the mount options. +.PP +During the build process each enclave page is assigned protection bits, +as part of +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES). +These permissions are also the maximum permissions to which the page can be be mapped. +If +.BR mmap (2) +is called with surpassing permissions, +it will return +.B -EACCES. +If +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES) +is called after +.BR mmap (2) +with lower permissions, +the process will eventually receive a +.BR SIGBUS +signal, +once it accesses the page for the first time. +.SH VERSIONS +The SGX feature was added in Linux 5.11. +.SH SEE ALSO +.BR ioctl (2), +.BR mmap (2), +.BR mprotect (2)
Signature · 1 line
2.32.0
Jarkko Sakkinen
maintainerQuoted 18 lines · Jarkko Sakkinen
Cc Dave Hansen <[email protected]>Cc Reinette Chatre <[email protected]>Signed-off-by Jarkko Sakkinen <[email protected]>---
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 covermmap()
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
Quoted 8 lines
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.
Can be previewed with e.g. "man man7/sgx.7", and also "yelp man7/sgx.7" works fine.
/Jarkko
Hello Jarkko
Quoted 63 lines · Jarkko Sakkinen
Cc Dave Hansen <[email protected]>Cc Reinette Chatre <[email protected]>Signed-off-by Jarkko Sakkinen <[email protected]>---
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 covermmap()
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 | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 156 insertions(+) create mode 100644 man7/sgx.7man7/sgx.7 new file +26
-0@@ -0,0 +1,156 @@ +.\" 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
man7/sgx.7 line 35
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man7/sgx.7 new file +9
-0+sgx - overview of Software Guard eXtensions +.SH SYNOPSIS +.EX +.B #include <asm/sgx.h> +.PP +.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);" +.EE +.SH DESCRIPTION +Intel Software Guard eXtensions (SGX) allow applications to host,
s/host,/host/
man7/sgx.7 line 38
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man7/sgx.7 new file +3
-0+enclaves, +protected executable objects in memory. +As software entities enclaves are instances of
s/entities/entities,/
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+.I
/dev/sgx_enclave.
What does the previous sentence mean? I'm sorry, it's not very clear.
Quoted 2 lines
+.PP
+SGX can be available only if the kernel was configured and built with the
s/can be/is/
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+.B
CONFIG_X86_SGXman7/sgx.7 new file +11
-0+option. +You can verify that both the kernel and hardware have SGX enabled by +checking that "sgx" appears in the +.I flags +field in +.IR /proc/cpuinfo . +.PP +SGX must be enabled in BIOS. +If SGX appears to be unsupported, +ensure that SGX is enabled in the BIOS. +If a BIOS presents a choice between
man7/sgx.7 line 63
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man7/sgx.7 new file +10
-0+.I Enabled +and +.I Software Enabled +modes for SGX, +choose +.I Enabled. +.PP +Enclaves are shared objects, meaning that +they can be shared with a +.BR cmsg (3),
How do they get shared with cmg()? This is unclear? Do you mean by passing a file descriptor over a UNIX domain socket, or something else?
man7/sgx.7 line 71
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man7/sgx.7 new file +8
-0+and inherited in a fork. +.SS Address space +The address range for an enclave must be reserved with +.BR mmap (2). +This must happen before the enclave construction can begin, +because the enclave page addresses are fixed during its build time. +.PP +The CPU requires the size of the enclave to be power of two,
Must the size also be >= page size? If so, that should be mentioned.
Quoted 16 lines
man7/sgx.7 new file +14
-0+and the base address to be naturally aligned with the size. +An appropriate address range can be found by an anonymous mapping: +.PP +.EX +void *area = mmap(NULL, size * 2, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, + -1, 0); + +/* Find the first address aligned to the size within the range. */ +void *base = ((uint64_t)area + size - 1) & ~(size - 1); +.EE +.PP +.SS Ioctls +Enclaves are managed with the +.BR ioctl (2)
man7/sgx.7 line 93
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man7/sgx.7 new file +8
-0+interface defined and documented in +.IR <asm/sgx.h>: +.TP +.IB SGX_IOC_ENCLAVE_CREATE +Create SGX Enclave Control Structure (SECS) for an enclave. +SECS is a hardware defined structure, +which contains the properties of an enclave, +such as its base address and size.
Add a sentence:
[[
The ioctl argument has the type
.IR "struct\ *sgx_enclave_create" .
]]
(I think this sentence helps the reader orient a little, when reading the header file.)
Quoted 3 lines
+.TP
+.IBSGX_IOC_ENCLAVE_ADD_PAGES
+Populate a range of enclave pages with the page data provided by the caller.
Add a sentence:
[[
The ioctl argument has the type
.IR "struct\ *sgx_enclave_add_pages" .
]]
Quoted 3 lines
+.TP
+.IBSGX_IOC_ENCLAVE_INIT
+Tell the CPU the prepare the enclave for use.
s/the prepare/to prepare/
man7/sgx.7 line 101
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man7/sgx.7 new file +2
-0+After a successful initialization, +no new pages can be added to the enclave.
Add a sentence:
[[
The ioctl argument has the type
.IR "struct\ *sgx_enclave_init" .
]]
Just looking in the header file, does SGX_IOC_ENCLAVE_PROVISION also need to be mentioned?
Quoted 2 lines
+.PP
+The details of what these operations actually mean in the hardware level can be
s/in/at/
man7/sgx.7 line 106
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man7/sgx.7 new file +3
-0+found in the Intel Software Developers Manual. +.SS vDSO +A process can access enclave by entering into its address space through
s/enclave/an enclave/
man7/sgx.7 line 113
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man7/sgx.7 new file +7
-0+a set of entry points, +which must be defined during the construction process. +This requires a complex sequence of CPU instructions, +and kernel assisted exception handling. +For these reasons, +it is encapsulated into +vDSO interface,
s/vDSO/a vDSO/
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+provided by
+.BRvdso_sgx_enter_enclave_t,
s/,/ ,/
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+which is located in
s/located/declared/ ?
man7/sgx.7 line 124
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+.IR <
asm/sgx.h>.
+.SS Permissionsman7/sgx.7 new file +6
-0+In order to build an enclave, a process must be able to call +.IR mmap (2) +with +.IR PROT_EXEC +set, +because like for any other type of executable,
s/because like for any/because, as with any/
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+the page table permissions must be set appropriately.
s/permissions/protections/
man7/sgx.7 line 135
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man7/sgx.7 new file +10
-0+Therefore, +.I /dev/sgx_enclave +must reside in a partition, +which is not mounted with +.B noexec +set in the mount options. +.PP +During the build process each enclave page is assigned protection bits, +as part of +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES).
In the previous sentence, you use "protections". In the following sentences you use "permissions". Best to be consistent. Let's use "protections", as per mmap(2).
man7/sgx.7 line 139
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man7/sgx.7 new file +4
-0+These permissions are also the maximum permissions to which the page can be be mapped. +If +.BR mmap (2) +is called with surpassing permissions,
s/surpassing/unexpected/
s/permissions/protections/
man7/sgx.7 line 147
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man7/sgx.7 new file +8
-0+it will return +.B -EACCES. +If +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES) +is called after +.BR mmap (2) +with lower permissions, +the process will eventually receive a
I want to check the wording here, since "eventually" is often a false friend for nonnative speakers.
In English, "eventually" means: at some (unknown) time in the future, something WILL happen. In other words, the happening is certain, but the timing is not. In various European languages, a similar sounding word in many cases has the sense of "possibly" or "may happen". Which do you mean to say?
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+.BR SIGBUS
man7/sgx.7 new file +8
-0+signal, +once it accesses the page for the first time. +.SH VERSIONS +The SGX feature was added in Linux 5.11. +.SH SEE ALSO +.BR ioctl (2), +.BR mmap (2), +.BR mprotect (2)
Signature · 3 lines
Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
Jarkko Sakkinen
maintainerQuoted 69 lines · Michael Kerrisk (man-pages)
Hello Jarkko
Quoted 66 lines · Jarkko Sakkinen
Cc Dave Hansen <[email protected]>Cc Reinette Chatre <[email protected]>Signed-off-by Jarkko Sakkinen <[email protected]>---
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 covermmap()
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 | 156 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 156 insertions(+) create mode 100644 man7/sgx.7man7/sgx.7 new file +29
-0@@ -0,0 +1,156 @@ +.\" 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 +.EX
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man7/sgx.7 line 35
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man7/sgx.7 new file +6
-0+.B #include <asm/sgx.h> +.PP +.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);" +.EE +.SH DESCRIPTION +Intel Software Guard eXtensions (SGX) allow applications to host,s/host,/host/
+1
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man7/sgx.7 line 38
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man7/sgx.7 new file +3
-0+enclaves, +protected executable objects in memory. +As software entities enclaves are instances ofs/entities/entities,/
+1
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man7/sgx.7 line 39
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man7/sgx.7 new file +1
-0+.I /dev/sgx_enclave.What does the previous sentence mean? I'm sorry, it's not very clear.
OK, I'll try to explain.
Enclaves are blobs of executable code, running inside a CPU enforced "container", which is mapped to the process address space. It has a fixed set of entry points, defined when the enclave is created.
An entry point can be passed to ENCLU opcode's subfunction EENTER, which transforms a hardware thread to enclave mode and starts executing inside the enclave. Any memory access from a thread outside the enclave causes a segfault.
A process hosting an enclave, needs to handle invalid opcode CPU exceptions that the enclave generates, because many common opcodes, e.g. SYSCALL and RDTSC are not allowed inside enclaves.
That's why EENTER is wrapped inside a vDSO. When a CPU exception happens, kernel and the vDSO code delegate, the exception number, error code and address back to the caller.
E.g. the caller can then work as a delegate for a syscall.
Any opcode that would cause a jump outside the enclave causes a CPU exception. The only way explicit way to leave the enclave is ENCLU opcode subfunction EEXIT, which moves the hardware thread away from the enclave mode, and jumps to the given target address.
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man7/sgx.7 line 41
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man7/sgx.7 new file +2
-0+.PP +SGX can be available only if the kernel was configured and built with thes/can be/is/
+1
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man7/sgx.7 new file +18
-0+.B CONFIG_X86_SGX +option. +You can verify that both the kernel and hardware have SGX enabled by +checking that "sgx" appears in the +.I flags +field in +.IR /proc/cpuinfo . +.PP +SGX must be enabled in BIOS. +If SGX appears to be unsupported, +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 +.I Enabled.
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man7/sgx.7 line 63
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man7/sgx.7 new file +4
-0+.PP +Enclaves are shared objects, meaning that +they can be shared with a +.BR cmsg (3),How do they get shared with
cmg()? This is unclear? Do you mean by passing a file descriptor over a UNIX domain socket, or something else?
A file descriptor over a UDS, yes.
Quoted 11 lines
man7/sgx.7 line 71
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man7/sgx.7 new file +8
-0+and inherited in a fork. +.SS Address space +The address range for an enclave must be reserved with +.BR mmap (2). +This must happen before the enclave construction can begin, +because the enclave page addresses are fixed during its build time. +.PP +The CPU requires the size of the enclave to be power of two,Must the size also be >= page size? If so, that should be mentioned.
Yes, I changed this to:
"
The CPU requires the size of the enclave to be power of two, at least size of a one page,
and the base address to be naturally aligned with the size. "
Quoted 25 lines
Quoted 12 lines
man7/sgx.7 new file +12
-0+and the base address to be naturally aligned with the size. +An appropriate address range can be found by an anonymous mapping: +.PP +.EX +void *area = mmap(NULL, size * 2, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, + -1, 0); + +/* Find the first address aligned to the size within the range. */ +void *base = ((uint64_t)area + size - 1) & ~(size - 1); +.EE +.PP +.SS Ioctlsman7/sgx.7 line 93
Quoted 10 lines
man7/sgx.7 new file +10
-0+Enclaves are managed with the +.BR ioctl (2) +interface defined and documented in +.IR <asm/sgx.h>: +.TP +.IB SGX_IOC_ENCLAVE_CREATE +Create SGX Enclave Control Structure (SECS) for an enclave. +SECS is a hardware defined structure, +which contains the properties of an enclave, +such as its base address and size.Add a sentence:
Quoted 7 lines
[[
The ioctl argument has the type
.IR "struct\*sgx_enclave_create" .
]](I think this sentence helps the reader orient a little, when reading the header file.)
+1
Quoted 10 lines
man7/sgx.7 line 96
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man7/sgx.7 new file +3
-0+.TP +.IB SGX_IOC_ENCLAVE_ADD_PAGES +Populate a range of enclave pages with the page data provided by the caller.Add a sentence:
[[
The ioctl argument has the type
.IR "struct\*sgx_enclave_add_pages" .
]]
+1
Quoted 5 lines
man7/sgx.7 line 99
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man7/sgx.7 new file +3
-0+.TP +.IB SGX_IOC_ENCLAVE_INIT +Tell the CPU the prepare the enclave for use.s/the prepare/to prepare/
+1
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man7/sgx.7 line 101
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man7/sgx.7 new file +2
-0+After a successful initialization, +no new pages can be added to the enclave.Add a sentence:
[[
The ioctl argument has the type
.IR "struct\*sgx_enclave_init" .
]]
+1
Quoted 2 lines
Just looking in the header file, does
SGX_IOC_ENCLAVE_PROVISIONalso need to be mentioned?
It's a topic of its own. I would focus now on these basic ioctl's, and contribute that part once these are in shape. It's disjoint in the sense that you can create and run enclaves without provisinioning.
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man7/sgx.7 line 103
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man7/sgx.7 new file +2
-0+.PP +The details of what these operations actually mean in the hardware level can bes/in/at/
+1
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man7/sgx.7 line 106
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man7/sgx.7 new file +3
-0+found in the Intel Software Developers Manual. +.SS vDSO +A process can access enclave by entering into its address space throughs/enclave/an enclave/
+1
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man7/sgx.7 line 113
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man7/sgx.7 new file +7
-0+a set of entry points, +which must be defined during the construction process. +This requires a complex sequence of CPU instructions, +and kernel assisted exception handling. +For these reasons, +it is encapsulated into +vDSO interface,s/vDSO/a vDSO/
+1
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man7/sgx.7 line 115
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man7/sgx.7 new file +2
-0+provided by +.BR vdso_sgx_enter_enclave_t,s/,/ ,/
+1
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man7/sgx.7 line 116
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man7/sgx.7 new file +1
-0+which is located ins/located/declared/ ?
+1
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man7/sgx.7 line 124
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man7/sgx.7 new file +8
-0+.IR <asm/sgx.h>. +.SS Permissions +In order to build an enclave, a process must be able to call +.IR mmap (2) +with +.IR PROT_EXEC +set, +because like for any other type of executable,s/because like for any/because, as with any/
+1
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man7/sgx.7 line 125
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man7/sgx.7 new file +1
-0+the page table permissions must be set appropriately.s/permissions/protections/
+1
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man7/sgx.7 new file +6
-0+Therefore, +.I /dev/sgx_enclave +must reside in a partition, +which is not mounted with +.B noexec +set in the mount options.
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man7/sgx.7 line 135
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man7/sgx.7 new file +4
-0+.PP +During the build process each enclave page is assigned protection bits, +as part of +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES).In the previous sentence, you use "protections". In the following sentences you use "permissions". Best to be consistent. Let's use "protections", as per mmap(2).
OK, I'll use that consistently from now on.
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man7/sgx.7 line 139
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man7/sgx.7 new file +4
-0+These permissions are also the maximum permissions to which the page can be be mapped. +If +.BR mmap (2) +is called with surpassing permissions,s/surpassing/unexpected/
s/permissions/protections/
Thanks, it's now all about protectinos.
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man7/sgx.7 line 147
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man7/sgx.7 new file +8
-0+it will return +.B -EACCES. +If +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES) +is called after +.BR mmap (2) +with lower permissions, +the process will eventually receive aI want to check the wording here, since "eventually" is often a false friend for nonnative speakers.
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In English, "eventually" means: at some (unknown) time in the future, something WILL happen. In other words, the happening is certain, but the timing is not. In various European languages, a similar sounding word in many cases has the sense of "possibly" or "may happen". Which do you mean to say?
It's actually the latter.
SIGBUS gets thrown exactly when a thread executing inside an enclave accesses a page, which has lower defined during the build time, than those of the VMA.
If that page is never accessed, then the enclave executes gracefully.
The idea is to keep an invariant that the protections defined during the creation cannot be crossed. When/If we ever consider hooking into to the various LSM's, the access control decisions need to happen during the build time. That's why need to have this type of invariant already in place.
Thank you for the feedback. I marked just "+1" for trivial fixups.
/Jarkko