diff mbox series

[v10] sgx.7: New page with overview of Software Guard eXtensions (SGX)

Message ID 20211130175007.22903-1-jarkko@kernel.org (mailing list archive)
State New, archived
Headers show
Series [v10] sgx.7: New page with overview of Software Guard eXtensions (SGX) | expand

Commit Message

Jarkko Sakkinen Nov. 30, 2021, 5:50 p.m. UTC 
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
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 | 147 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 147 insertions(+)
 create mode 100644 man7/sgx.7

Comments

Reinette Chatre Dec. 8, 2021, 10:11 p.m. UTC | #1 
Hi Jarkko,

On 11/30/2021 9:50 AM, Jarkko Sakkinen wrote:
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

...

> +.TH SGX 7 2021\-02\-02 "Linux" "Linux Programmer's Manual"
> +.PP
> +sgx - overview of Software Guard eXtensions

Is the "overview of" text necessary?

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

I view the man page output using "man -l man7/sgx.7" and when I do so 
the above line is unbalanced: "enclave" and (unexpectedly) the comma are 
underlined and the line is displayed with a single instance of a double 
quote: 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.
> +.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
> +.I /dev/sgx_enclave.
> +They have a fixed set of entry points,
> +defined when the enclave is built.
> +.PP
> +SGX can be only available if the kernel is configured and built with the

can be only -> can only be?

> +.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
> +.I Enabled.

Earlier there is the underlined "/proc/cpuinfo" text followed by a 
period and here the "Enabled" text is followed by a period. In this 
instance the period is also underlined while previously it is not. 
Looking at some other man pages it seems that the custom is that the 
period should not be underlined and I will continue to point out 
instances I noticed where this is not the case.

> +.PP
> +.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);
> +.EE
> +.PP
> +The enclave file descriptor itself can be then mapped with the
> +.BR MAP_FIXED
> +flag set to the carved out memory.
> +.SS Construction
> +An enclave instance is created by opening
> +.I /dev/sgx_enclave.

Underlined period above.

> +Its contents are populated with the
> +.BR ioctl (2)
> +interface in
> +.IR <asm/sgx.h>:

Here also, should the above colon perhaps not be underlined?

> +.TP
> +.IB 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.
> +.IB SGX_IOC_ENCLAVE_CREATE
> +is a one-shot call that fixes enclave's address and

fixes enclave's -> fixes the enclave's ?

> +size for the rest of its life-cycle.
> +.TP
> +.IB SGX_IOC_ENCLAVE_ADD_PAGES
> +Fill a range of the enclaves pages with the caller provided data and protection bits.

Should this be "the enclave's pages"?

> +Memory mappings of the enclave can only have protection bits set,
> +which are defined in this ioctl.

This is a bit hard to understand. How about "Memory mappings of the 
enclave can only set protection bits that are defined in this ioctl."

> +The pages added are either regular memory pages for code and data

regular memory pages -> regular pages?

,
> +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
> +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) page are the entry points to the enclave,

page are -> pages are ?

> +which further define an offset inside the enclave where the execution begins.
> +The entry points are invoked with
> +.I __vdso_sgx_enter_enclave.

Underlined period above.

> +The prototype for the vDSO is defined by
> +.BR vdso_sgx_enter_enclave_t
> +in
> +.IR <asm/sgx.h>.

Same above with the underlining of "."

> +.SS Permissions
> +.PP
> +During the build process each enclave page is assigned protection bits,
> +as part of
> +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES).
> +These protections are also the maximum protections to which the page can be be mapped.

to which -> with which ?

> +If
> +.BR mmap (2)_

Unexpected "_" above

> +is called with higher protections than those defined during the build,
> +it will return
> +.B -EACCES.
> +If
> +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES)
> +is called after
> +.BR mmap (2)
> +with lower protections,
> +the caller receives
> +.BR SIGBUS,
> +once it accesses the page for the first time.
> +.SH VERSIONS
> +The SGX feature was added in Linux 5.11.

This does not document the SGX_IOC_VEPC_REMOVE ioctl that was added in 
v5.16. How do you envision additions to this page as new features are 
added to the Linux support of SGX?

> +.SH SEE ALSO
> +.BR ioctl (2),
> +.BR mmap (2),
> +.BR mprotect (2)
> \ No newline at end of file
> 

Reinette
Jarkko Sakkinen Dec. 11, 2021, 3:19 p.m. UTC | #2 
On Wed, 2021-12-08 at 14:11 -0800, Reinette Chatre wrote:
> Hi Jarkko,
> 
> On 11/30/2021 9:50 AM, Jarkko Sakkinen wrote:
> > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> 
> ...
> 
> > +.TH SGX 7 2021\-02\-02 "Linux" "Linux Programmer's Manual"
> > +.PP
> > +sgx - overview of Software Guard eXtensions
> 
> Is the "overview of" text necessary?

It's more or less a convention:

$ git grep "overview of" man7 | wc -l
29

> > +.SH SYNOPSIS
> > +.EX
> > +.B #include <asm/sgx.h>
> > +.PP
> > +.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);"
> 
> I view the man page output using "man -l man7/sgx.7" and when I do so 
> the above line is unbalanced: "enclave" and (unexpectedly) the comma are 
> underlined and the line is displayed with a single instance of a double 
> quote: enclave = open("/dev/sgx_enclave, O_RDWR);

After some trial and error, and looking at symlink.7, this seems to
fix it:

-.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);"
+.IB enclave " = open(""/dev/sgx_enclave"", O_RDWR);"

Does this fix for you?

> > +.EE
> > +.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
> > +.I /dev/sgx_enclave.

.IR /dev/sgx_enclave .

> > +They have a fixed set of entry points,
> > +defined when the enclave is built.
> > +.PP
> > +SGX can be only available if the kernel is configured and built with the
> 
> can be only -> can only be?

Agreed, I'll fix this.

> > +.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
> > +.I Enabled.
> 
> Earlier there is the underlined "/proc/cpuinfo" text followed by a 
> period and here the "Enabled" text is followed by a period. In this 
> instance the period is also underlined while previously it is not. 
> Looking at some other man pages it seems that the custom is that the 
> period should not be underlined and I will continue to point out 
> instances I noticed where this is not the case.

This most related to my very weak understanding of troff syntax.

I changed it to:

-.I Enabled.
+.IR Enabled .

This does seem to fix the issue, and aligns with this:

https://www.gnu.org/software/groff/manual/html_node/Man-font-macros.html

> > +.PP
> > +.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);
> > +.EE
> > +.PP
> > +The enclave file descriptor itself can be then mapped with the
> > +.BR MAP_FIXED
> > +flag set to the carved out memory.
> > +.SS Construction
> > +An enclave instance is created by opening
> > +.I /dev/sgx_enclave.
> 
> Underlined period above.

Thanks. I spotted similar error also early in the text.

> > +Its contents are populated with the
> > +.BR ioctl (2)
> > +interface in
> > +.IR <asm/sgx.h>:
> 
> Here also, should the above colon perhaps not be underlined?

Yeah, similarly:

.IR <asm/sgx.h>:
+.IR <asm/sgx.h> :

> > +.TP
> > +.IB 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.
> > +.IB SGX_IOC_ENCLAVE_CREATE
> > +is a one-shot call that fixes enclave's address and
> 
> fixes enclave's -> fixes the enclave's ?

Ack.

> > +size for the rest of its life-cycle.
> > +.TP
> > +.IB SGX_IOC_ENCLAVE_ADD_PAGES
> > +Fill a range of the enclaves pages with the caller provided data and protection bits.
> 
> Should this be "the enclave's pages"?

I think so.

> > +Memory mappings of the enclave can only have protection bits set,
> > +which are defined in this ioctl.
> 
> This is a bit hard to understand. How about "Memory mappings of the 
> enclave can only set protection bits that are defined in this ioctl."

Changed, thanks.

> > +The pages added are either regular memory pages for code and data
> 
> regular memory pages -> regular pages?

Changed.

> 
> ,
> > +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
> > +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) page are the entry points to the enclave,
> 
> page are -> pages are ?

Thanks, good catch.

> > +which further define an offset inside the enclave where the execution begins.
> > +The entry points are invoked with
> > +.I __vdso_sgx_enter_enclave.
> 
> Underlined period above.

.I __vdso_sgx_enter_enclave.
+.IR __vdso_sgx_enter_enclave .

> > +The prototype for the vDSO is defined by
> > +.BR vdso_sgx_enter_enclave_t
> > +in
> > +.IR <asm/sgx.h>.
> 
> Same above with the underlining of "."
> 
> > +.SS Permissions
> > +.PP
> > +During the build process each enclave page is assigned protection bits,
> > +as part of
> > +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES).
> > +These protections are also the maximum protections to which the page can be be mapped.
> 
> to which -> with which ?

Ack.

> 
> > +If
> > +.BR mmap (2)_
> 
> Unexpected "_" above

Thanks.

> 
> > +is called with higher protections than those defined during the build,
> > +it will return
> > +.B -EACCES.
> > +If
> > +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES)
> > +is called after
> > +.BR mmap (2)
> > +with lower protections,
> > +the caller receives
> > +.BR SIGBUS,
> > +once it accesses the page for the first time.
> > +.SH VERSIONS
> > +The SGX feature was added in Linux 5.11.
> 
> This does not document the SGX_IOC_VEPC_REMOVE ioctl that was added in 
> v5.16. How do you envision additions to this page as new features are 
> added to the Linux support of SGX?

I started this before any of KVM stuff was in upstream. It'd be better
to get the basic ioctl's done first. I cannot really give estimate for
vepc at this point.

For future features (e.g. SGX2), the expectation is that the feature is
supported by an associated man page update.

> > +.SH SEE ALSO
> > +.BR ioctl (2),
> > +.BR mmap (2),
> > +.BR mprotect (2)
> > \ No newline at end of file
> > 
> 
> Reinette

Thanks for valuable feedback.

/Jarkko
Reinette Chatre Dec. 13, 2021, 7:51 p.m. UTC | #3 
Hi Jarkko,

On 12/11/2021 7:19 AM, Jarkko Sakkinen wrote:
> On Wed, 2021-12-08 at 14:11 -0800, Reinette Chatre wrote:
>> On 11/30/2021 9:50 AM, Jarkko Sakkinen wrote:

...

>>> +.SH SYNOPSIS
>>> +.EX
>>> +.B #include <asm/sgx.h>
>>> +.PP
>>> +.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);"
>>
>> I view the man page output using "man -l man7/sgx.7" and when I do so
>> the above line is unbalanced: "enclave" and (unexpectedly) the comma are
>> underlined and the line is displayed with a single instance of a double
>> quote: enclave = open("/dev/sgx_enclave, O_RDWR);
> 
> After some trial and error, and looking at symlink.7, this seems to
> fix it:
> 
> -.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);"
> +.IB enclave " = open(""/dev/sgx_enclave"", O_RDWR);"
> 
> Does this fix for you?

Yes, thank you. When looking at your updated patch I see that only 
enclave is underlined and the quotes are matching.

...

>>> +is called with higher protections than those defined during the build,
>>> +it will return
>>> +.B -EACCES.
>>> +If
>>> +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES)
>>> +is called after
>>> +.BR mmap (2)
>>> +with lower protections,
>>> +the caller receives
>>> +.BR SIGBUS,
>>> +once it accesses the page for the first time.
>>> +.SH VERSIONS
>>> +The SGX feature was added in Linux 5.11.
>>
>> This does not document the SGX_IOC_VEPC_REMOVE ioctl that was added in
>> v5.16. How do you envision additions to this page as new features are
>> added to the Linux support of SGX?
> 
> I started this before any of KVM stuff was in upstream. It'd be better
> to get the basic ioctl's done first. I cannot really give estimate for
> vepc at this point.

SGX_IOC_VEPC_REMOVE_ALL can be found in v5.16.

> For future features (e.g. SGX2), the expectation is that the feature is
> supported by an associated man page update.
> 

ok, thank you.

Reinette
Jarkko Sakkinen Dec. 22, 2021, 12:39 a.m. UTC | #4 
On Mon, Dec 13, 2021 at 11:51:36AM -0800, Reinette Chatre wrote:
> Hi Jarkko,
> 
> On 12/11/2021 7:19 AM, Jarkko Sakkinen wrote:
> > On Wed, 2021-12-08 at 14:11 -0800, Reinette Chatre wrote:
> > > On 11/30/2021 9:50 AM, Jarkko Sakkinen wrote:
> 
> ...
> 
> > > > +.SH SYNOPSIS
> > > > +.EX
> > > > +.B #include <asm/sgx.h>
> > > > +.PP
> > > > +.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);"
> > > 
> > > I view the man page output using "man -l man7/sgx.7" and when I do so
> > > the above line is unbalanced: "enclave" and (unexpectedly) the comma are
> > > underlined and the line is displayed with a single instance of a double
> > > quote: enclave = open("/dev/sgx_enclave, O_RDWR);
> > 
> > After some trial and error, and looking at symlink.7, this seems to
> > fix it:
> > 
> > -.IB enclave " = open(""/dev/sgx_enclave", " O_RDWR);"
> > +.IB enclave " = open(""/dev/sgx_enclave"", O_RDWR);"
> > 
> > Does this fix for you?
> 
> Yes, thank you. When looking at your updated patch I see that only enclave
> is underlined and the quotes are matching.
> 
> ...
> 
> > > > +is called with higher protections than those defined during the build,
> > > > +it will return
> > > > +.B -EACCES.
> > > > +If
> > > > +.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES)
> > > > +is called after
> > > > +.BR mmap (2)
> > > > +with lower protections,
> > > > +the caller receives
> > > > +.BR SIGBUS,
> > > > +once it accesses the page for the first time.
> > > > +.SH VERSIONS
> > > > +The SGX feature was added in Linux 5.11.
> > > 
> > > This does not document the SGX_IOC_VEPC_REMOVE ioctl that was added in
> > > v5.16. How do you envision additions to this page as new features are
> > > added to the Linux support of SGX?
> > 
> > I started this before any of KVM stuff was in upstream. It'd be better
> > to get the basic ioctl's done first. I cannot really give estimate for
> > vepc at this point.
> 
> SGX_IOC_VEPC_REMOVE_ALL can be found in v5.16.

I'd get the basic API documentation ready first and continue to that after
it is final.

> > For future features (e.g. SGX2), the expectation is that the feature is
> > supported by an associated man page update.
> > 
> 
> ok, thank you.
> 
> Reinette

/Jarkko
diff mbox series

Patch

diff --git a/man7/sgx.7 b/man7/sgx.7
new file mode 100644
index 000000000..696d60e18
--- /dev/null
+++ b/man7/sgx.7
@@ -0,0 +1,147 @@ 
+.\" 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.
+.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
+.I /dev/sgx_enclave.
+They have a fixed set of entry points,
+defined when the enclave is built.
+.PP
+SGX can be only 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
+.I Enabled.
+.PP
+.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);
+.EE
+.PP
+The enclave file descriptor itself can be then mapped with the
+.BR MAP_FIXED
+flag set to the carved out memory.
+.SS Construction
+An enclave instance is created by opening
+.I /dev/sgx_enclave.
+Its contents are populated with the
+.BR ioctl (2)
+interface in
+.IR <asm/sgx.h>:
+.TP
+.IB 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.
+.IB SGX_IOC_ENCLAVE_CREATE
+is a one-shot call that fixes enclave's address and
+size for the rest of its life-cycle.
+.TP
+.IB SGX_IOC_ENCLAVE_ADD_PAGES
+Fill a range of the enclaves pages with the caller provided data and protection bits.
+Memory mappings of the enclave can only have protection bits set,
+which are defined in this ioctl.
+The pages added are either regular memory 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
+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) page 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
+.I __vdso_sgx_enter_enclave.
+The prototype for the vDSO is defined by
+.BR vdso_sgx_enter_enclave_t
+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).
+These protections are also the maximum protections to 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.
+If
+.BR ioctl(SGX_IOC_ENCLAVE_ADD_PAGES)
+is called after
+.BR mmap (2)
+with lower protections,
+the caller receives
+.BR SIGBUS,
+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)
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