V2 [PATCH] x86/CET: Document glibc.tune.x86_ibt and glibc.tune.x86_shstk

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Tue, Jul 17, 2018 at 10:22 PM, Rical Jasan <rj@2c3t.io> wrote:
> On 07/17/2018 08:04 PM, H.J. Lu wrote:
>> diff --git a/manual/tunables.texi b/manual/tunables.texi
>> index be33c9fc79..7998b3b7e6 100644
>> --- a/manual/tunables.texi
>> +++ b/manual/tunables.texi
>> @@ -356,3 +356,26 @@ to set threshold in bytes for non temporal store.
>>
>>  This tunable is specific to i386 and x86-64.
>>  @end deftp
>> +
>> +@deftp Tunable glibc.tune.x86_ibt
>> +The @code{glibc.tune.x86_ibt=[on|off|permissive]} tunable allows the user> +to control how indirect branch tracking (IBT) should be enabled.
>
> It seems out of place to list the available options like that in the
> textual context here (for reasons similar to why we don't write function
> calls within paragraphs; e.g., @code{foo(x, y)}), but I do see some
> precedent with other tunables currently in the manual.  Instead, I would
> follow up the above sentence with, "Accepted values are @code{on},
> @code{off}, and @code{permissive}."

Fixed.

>> +@code{on} always turns on IBT regardless of whether IBT is enabled in the
>> +executable and its dependent shared libraries.  @code{off} always turns
>> +off IBT regardless of whether IBT is enabled in the executable and its
>> +dependent shared libraries.  @code{permissive} is the same as the default.
>
> Which is the default and what does it do?

Fixed.

>> +This tunable is specific to i386 and x86-64.
>> +@end deftp
>> +
>> +@deftp Tunable glibc.tune.x86_shstk
>> +The @code{glibc.tune.x86_shstk=[on|off|permissive]} tunable allows the
>> +user to control how shadow stack (SHSTK) should be enabled.  @code{on}
>
> Should "shadow stack" be prefixed with a definite article ("the shadow
> stack")?  Similarly for SHSTK below.

I don't think SHSTK needs a "the" prefix as we don't use the SSE.

>> +always turns on SHSTK regardless of whether SHSTK is enabled in the
>> +executable and its dependent shared libraries.  @code{off} always turns
>> +off SHSTK regardless of whether SHSTK is enabled in the executable and
>> +its dependent shared libraries.  @code{permissive} turns off SHSTK when
>> +dlopening a legacy shared library, instead of returns an error.
>
> "instead of returning"?

Fixed.

> Also, what does "legacy" mean in this context?

Fixed/

>> +This tunable is specific to i386 and x86-64.
>> +@end deftp
>

Here is the updated patch.  OK for master?

Thanks.

-- 
H.J.

From d3954e238462ca5da54d9cf5b0b955dd8ee1b93c Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Tue, 17 Jul 2018 19:51:23 -0700
Subject: [PATCH] x86/CET: Document glibc.tune.x86_ibt and glibc.tune.x86_shstk

	* manual/tunables.texi: Document glibc.tune.x86_ibt and
	glibc.tune.x86_shstk.
---
 manual/tunables.texi | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/manual/tunables.texi b/manual/tunables.texi
index be33c9fc79..13426ce238 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -356,3 +356,31 @@ to set threshold in bytes for non temporal store.
 
 This tunable is specific to i386 and x86-64.
 @end deftp
+
+@deftp Tunable glibc.tune.x86_ibt
+The @code{glibc.tune.x86_ibt=[on|off|permissive]} tunable allows the user
+to control how indirect branch tracking (IBT) should be enabled.  Accepted
+values are @code{on}, @code{off}, and @code{permissive}.  @code{on} always
+turns on IBT regardless of whether IBT is enabled in the executable and
+its dependent shared libraries.  @code{off} always turns off IBT regardless
+of whether IBT is enabled in the executable and its dependent shared
+libraries.  @code{permissive} is the same as the default which disables
+IBT on non-CET executables and shared libraries.
+
+This tunable is specific to i386 and x86-64.
+@end deftp
+
+@deftp Tunable glibc.tune.x86_shstk
+The @code{glibc.tune.x86_shstk=[on|off|permissive]} tunable allows the
+user to control how the shadow stack (SHSTK) should be enabled.  Accepted
+values are @code{on}, @code{off}, and @code{permissive}.  @code{on}
+always turns on SHSTK regardless of whether SHSTK is enabled in the
+executable and its dependent shared libraries.  @code{off} always turns
+off SHSTK regardless of whether SHSTK is enabled in the executable and
+its dependent shared libraries.  @code{permissive} changes how dlopen
+works on non-CET shared libraries.  By default, when SHSTK is enabled,
+dlopening a non-CET shared library returns an error.  With
+@code{permissive}, it turns off SHSTK instead.
+
+This tunable is specific to i386 and x86-64.
+@end deftp
-- 
2.17.1