Re: [PATCH v11] sgx.7: New page with overview of Software Guard eXtensions (SGX)

Alejandro Colomar (man-pages)
2021-12-17T01:51:01Z

Hi Jarkko,

Please see some comments below.

Thanks,
Alex

On 12/11/21 16:33, Jarkko Sakkinen wrote:
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
> v11:
> * Address Reinette's remarks for v10:
> https://lore.kernel.org/linux-sgx/8f84b8e8-b478-bb81-4aa8-536df882a144@intel.com/
> 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 | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 146 insertions(+)
> create mode 100644 man7/sgx.7
>
> diff --git a/man7/sgx.7 b/man7/sgx.7
> new file mode 100644
> index 000000000..0b5aa87e9
> --- /dev/null
> +++ b/man7/sgx.7
> @@ -0,0 +1,146 @@
> +.\" 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 +.\" manual page may be incorrect or out-of-date.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

Please, add .nf here (see any man2 or man3 pages as an example).

groff(7):
.nf No filling or adjusting of output lines.

> +.EX
> +.B #include <asm/sgx.h>
> +.PP
> +.IB enclave " = open(""/dev/sgx_enclave"", O_RDWR);"

Sorry for not jumping here before. I read the thread but didn't have
the time to reply. What you wanted to use here is \(dq.

groff_man(7):
\(dq ASCII double-quote. Sometimes needed after macro
calls to prevent the interpretation of the ASCII
quotation mark character '"' as the beginning or
end of a macro argument.

So:

.IB enclave " = open(" \dq/dev/sgx_enclave\(dq ", O_RDWR);"

> +.EE

Please, add .fi here.

groff(7):
.fi Fill output lines.

> +.SH DESCRIPTION
> +Intel Software Guard eXtensions (SGX) allow applications to host
> +enclaves,
> +protected executable objects in 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 instances of
> +.IR /dev/sgx_enclave .
> +They have a fixed set of entry points,
> +defined when the enclave is built.
> +.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 .
> +.PP

.PP not necessary just before .SS or .SH. Please remove it.

> +.SS Memory mapping
> +The file descriptor for 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
> +.EX
> +void *area = mmap(NULL, size * 2, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS,
> + -1, 0);
> +
> +void *base = ((uint64_t)area + size - 1) & ~(size - 1);

Wouldn't uintptr_t(3) be better here (instead of uint64_t(3))?

Also, please add a space just after the cast, just for consistency with
other manual pages.

> +.EE
> +.PP

Please indent the above.

man-pages(7):
Indentation of structure definitions, shell session logs, and so on
When structure definitions, shell session logs, and so on are
included in running text, indent them by 4 spaces (i.e., a
block enclosed by .in +4n and .in), format them using the .EX
and EE macros, and surround them with suitable paragraph mark-
ers (either .PP or .IP). For example:

.PP
.in +4n
.EX
int
main(int argc, char *argv[])
{
return 0;
}
.EE
.in
.PP

> +The enclave file descriptor itself can be then mapped with the
> +.BR MAP_FIXED

This should be .B

groff_man(7):
.B [text]
Set text in bold. If the macro is given no argu-
ments, the text of the next input line is set in
bold.

Use bold for literal portions of syntax synopses,
for command-line options in running text, and for
literals that are major topics of the subject un-
der discussion; for example, this page uses bold
for macro and register names. In .EX/.EE examples
of interactive I/O (such as a shell session), set
only the user-typed input in bold.

[...]

.BR bold-text roman-text ...
Set each argument in bold and roman, alternately.

Any such change becomes effective with the first
use of
.BR .NH ,
.I after
the new alias is defined.

> +flag set to the carved out memory.
> +.SS Construction
> +An enclave instance is created by opening
> +.IR /dev/sgx_enclave .
> +Its contents are populated with the
> +.BR ioctl (2)
> +interface in
> +.IR <asm/sgx.h> :
> +.TP
> +.IB SGX_IOC_ENCLAVE_CREATE

This should be .B

> +Create SGX Enclave Control Structure (SECS) for the enclave.
> +SECS is a hardware defined structure,
> +which contains the global properties of an enclave.
> +.IB SGX_IOC_ENCLAVE_CREATE

Same here

> +is a one-shot call that fixes the enclave's address and
> +size for the rest of its life-cycle.
> +.TP
> +.IB SGX_IOC_ENCLAVE_ADD_PAGES

Same here.

> +Fill a range of the enclave's pages with the caller provided data and protection bits.
> +Memory mappings of the enclave can only set protection bits that are defined in this ioctl.
> +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
> +.IB SGX_IOC_ENCLAVE_INIT

Same here.

> +Initialize the enclave for the run-time.
> +After a successful initialization,
> +no new pages can be added to the enclave.
> +.SS Invocation
> +Thread control structure (TCS) pages are the entry points to the enclave,
> +which further define an offset inside the enclave where the execution begins.
> +The entry points are invoked with
> +.IR __vdso_sgx_enter_enclave .
> +The prototype for the vDSO is defined by
> +.BR vdso_sgx_enter_enclave_t

.I

Types go in italics. This is to be added to a future manual page
groff_man_style(7). Discussed here:
<https://lore.kernel.org/linux-man/20211112093536.hvifxgdtb2y6jzge@localhost.localdomain/>

> +in
> +.IR <asm/sgx.h> .
> +.SS Permissions
> +.PP
> +During the build process each enclave page is assigned protection bits,
> +as part of
> +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES).

Function calls go in italics.

man-pages(7):
Expressions, if not written on a separate indented line,
should be specified in italics. Again, the use of non-
breaking spaces may be appropriate if the expression is
inlined with normal text.

So this should use .IR, not .BR.

Also, a space before the period.

groff_man(7):
.IR italic-text roman-text ...
Set each argument in italics and roman, alter-
nately.

This is the first command of the
.IR prologue .

> +These protections are also the maximum protections with which the page can be be mapped.
> +If
> +.BR mmap (2)
> +is called with higher protections than those defined during the build,
> +it will return
> +.B -EACCES.

.BR and a space.

groff_man(7):
.BR bold-text roman-text ...
Set each argument in bold and roman, alternately.

Any such change becomes effective with the first
use of
.BR .NH ,
.I after
the new alias is defined.

> +If
> +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES)

.I

groff_man(7):
.I [text]
Set text in italics. If the macro is given no ar-
guments, the text of the next input line is set in
italics.

Use italics for file and path names, for environ-
ment variables, for enumeration or preprocessor
constants in C, for variable (user-determined)
portions of syntax synopses, for the first occur-
rence only of a technical concept being intro-
duced, for names of works of software (including
commands and functions, but excluding names of op-
erating systems or their kernels), and anywhere a
parameter requiring replacement by the user is en-
countered. An exception involves variable text in
a context that is already marked up in italics,
such as file or path names with variable compo-
nents; in such cases, follow the convention of
mathematical typography: set the file or path name
in italics as usual (see .IR below), but use roman
for the variable part, and italics again in run-
ning roman text when referring to the variable ma-
terial.

> +is called after
> +.BR mmap (2)
> +with lower protections,
> +the caller receives
> +.BR SIGBUS,

A space before the comma.

> +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)

--
Alejandro Colomar
Linux man-pages comaintainer; http://www.kernel.org/doc/man-pages/