[PATCH] prctl.2: Document PR_SET_MDWE and PR_GET_MDWE

[PATCH] prctl.2: Document PR_SET_MDWE and PR_GET_MDWE

[Florent Revest]

Memory-Deny-Write-Execute is a W^X process control originally introduced
by Joey Gouly. I'm the author of the PR_MDWE_NO_INHERIT flag.

Signed-off-by: Florent Revest <revest@chromium.org>
---
 man2/prctl.2 | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/man2/prctl.2 b/man2/prctl.2
index d845b0905..67e6e2ff0 100644
--- a/man2/prctl.2
+++ b/man2/prctl.2
@@ -2041,6 +2041,33 @@ the copy will be truncated.
 Return (as the function result)
 the full length of the auxiliary vector.
 \fIarg4\fP and \fIarg5\fP must be 0.
+.TP
+.BR PR_SET_MDWE " (since Linux 6.3)"
+.\" commit b507808ebce23561d4ff8c2aa1fb949fe402bc61
+Set the process' Memory-Deny-Write-Execute protection mask.
+.IR arg2
+must be a bitmask of:
+.RS
+.\"
+.TP
+.B PR_MDWE_REFUSE_EXEC_GAIN
+New memory mapping protections can't be writable and executable. Non-executable
+mappings can't become executable.
+.TP
+.B PR_MDWE_NO_INHERIT " (since Linux 6.6)"
+.\" commit 2a87e5520554034e8c423479740f95bea4a086a0
+Do not propagate MDWE protection to child processes on
+.BR fork (2).
+.TP
+Once protection bits are set, they can not be changed.
+.RE
+.TP
+.BR PR_GET_MDWE " (since Linux 6.3)"
+.\" commit b507808ebce23561d4ff8c2aa1fb949fe402bc61
+Return (as the function result) the Memory-Deny-Write-Execute protection mask.
+(See
+.B PR_SET_MDWE
+for information on the protection mask bits.)
 .SH RETURN VALUE
 On success,
 .BR PR_CAP_AMBIENT + PR_CAP_AMBIENT_IS_SET ,
-- 
2.42.0.582.g8ccd20d70d-goog

Re: [PATCH] prctl.2: Document PR_SET_MDWE and PR_GET_MDWE

[Alejandro Colomar]

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Hi Florent,

On Tue, Oct 03, 2023 at 05:50:10PM +0200, Florent Revest wrote:
> Memory-Deny-Write-Execute is a W^X process control originally introduced
> by Joey Gouly. I'm the author of the PR_MDWE_NO_INHERIT flag.
> 
> Signed-off-by: Florent Revest <revest@chromium.org>
> ---
>  man2/prctl.2 | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/man2/prctl.2 b/man2/prctl.2
> index d845b0905..67e6e2ff0 100644
> --- a/man2/prctl.2
> +++ b/man2/prctl.2
> @@ -2041,6 +2041,33 @@ the copy will be truncated.
>  Return (as the function result)
>  the full length of the auxiliary vector.
>  \fIarg4\fP and \fIarg5\fP must be 0.
> +.TP
> +.BR PR_SET_MDWE " (since Linux 6.3)"
> +.\" commit b507808ebce23561d4ff8c2aa1fb949fe402bc61
> +Set the process' Memory-Deny-Write-Execute protection mask.
> +.IR arg2
> +must be a bitmask of:
> +.RS
> +.\"
> +.TP
> +.B PR_MDWE_REFUSE_EXEC_GAIN
> +New memory mapping protections can't be writable and executable. Non-executable

Please use semantic newlines.

$ MANWIDTH=72 man man-pages | sed -n '/Use semantic newlines/,/^$/p'
   Use semantic newlines
       In the source of a manual page, new sentences should be started
       on  new  lines,  long  sentences  should be split into lines at
       clause breaks (commas, semicolons, colons, and so on), and long
       clauses should be split at phrase boundaries.  This convention,
       sometimes known as "semantic newlines", makes it easier to  see
       the  effect of patches, which often operate at the level of in‐
       dividual sentences, clauses, or phrases.

Thanks,
Alex

> +mappings can't become executable.
> +.TP
> +.B PR_MDWE_NO_INHERIT " (since Linux 6.6)"
> +.\" commit 2a87e5520554034e8c423479740f95bea4a086a0
> +Do not propagate MDWE protection to child processes on
> +.BR fork (2).
> +.TP
> +Once protection bits are set, they can not be changed.
> +.RE
> +.TP
> +.BR PR_GET_MDWE " (since Linux 6.3)"
> +.\" commit b507808ebce23561d4ff8c2aa1fb949fe402bc61
> +Return (as the function result) the Memory-Deny-Write-Execute protection mask.
> +(See
> +.B PR_SET_MDWE
> +for information on the protection mask bits.)
>  .SH RETURN VALUE
>  On success,
>  .BR PR_CAP_AMBIENT + PR_CAP_AMBIENT_IS_SET ,
> -- 
> 2.42.0.582.g8ccd20d70d-goog
> 

-- 
<https://www.alejandro-colomar.es/>

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Re: [PATCH] prctl.2: Document PR_SET_MDWE and PR_GET_MDWE

[Florent Revest]

On Sun, Oct 8, 2023 at 11:39 PM Alejandro Colomar <alx@kernel.org> wrote:
>
> Please use semantic newlines.
>
> $ MANWIDTH=72 man man-pages | sed -n '/Use semantic newlines/,/^$/p'
>    Use semantic newlines
>        In the source of a manual page, new sentences should be started
>        on  new  lines,  long  sentences  should be split into lines at
>        clause breaks (commas, semicolons, colons, and so on), and long
>        clauses should be split at phrase boundaries.  This convention,
>        sometimes known as "semantic newlines", makes it easier to  see
>        the  effect of patches, which often operate at the level of in‐
>        dividual sentences, clauses, or phrases.

Oops, looks like I missed the "Style guide" section of CONTRIBUTING,
sorry about that! I will fix it and re-spin :)

Re: [PATCH] prctl.2: Document PR_SET_MDWE and PR_GET_MDWE

[Catalin Marinas]

On Tue, Oct 03, 2023 at 05:50:10PM +0200, Florent Revest wrote:
> Memory-Deny-Write-Execute is a W^X process control originally introduced
> by Joey Gouly. I'm the author of the PR_MDWE_NO_INHERIT flag.
> 
> Signed-off-by: Florent Revest <revest@chromium.org>
> ---
>  man2/prctl.2 | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/man2/prctl.2 b/man2/prctl.2
> index d845b0905..67e6e2ff0 100644
> --- a/man2/prctl.2
> +++ b/man2/prctl.2
> @@ -2041,6 +2041,33 @@ the copy will be truncated.
>  Return (as the function result)
>  the full length of the auxiliary vector.
>  \fIarg4\fP and \fIarg5\fP must be 0.
> +.TP
> +.BR PR_SET_MDWE " (since Linux 6.3)"
> +.\" commit b507808ebce23561d4ff8c2aa1fb949fe402bc61
> +Set the process' Memory-Deny-Write-Execute protection mask.
> +.IR arg2
> +must be a bitmask of:
> +.RS
> +.\"
> +.TP
> +.B PR_MDWE_REFUSE_EXEC_GAIN
> +New memory mapping protections can't be writable and executable. Non-executable
> +mappings can't become executable.
> +.TP
> +.B PR_MDWE_NO_INHERIT " (since Linux 6.6)"
> +.\" commit 2a87e5520554034e8c423479740f95bea4a086a0
> +Do not propagate MDWE protection to child processes on

Should this mention that PR_MDWE_NO_INHERIT requires
PR_MDWE_REFUSE_EXEC_GAIN (unless I forgot how this was supposed to
work).

-- 
Catalin

Re: [PATCH] prctl.2: Document PR_SET_MDWE and PR_GET_MDWE

[Florent Revest]

On Mon, Oct 9, 2023 at 6:34 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
>
> On Tue, Oct 03, 2023 at 05:50:10PM +0200, Florent Revest wrote:
> > +.B PR_MDWE_REFUSE_EXEC_GAIN
> > +New memory mapping protections can't be writable and executable. Non-executable
> > +mappings can't become executable.
> > +.TP
> > +.B PR_MDWE_NO_INHERIT " (since Linux 6.6)"
> > +.\" commit 2a87e5520554034e8c423479740f95bea4a086a0
> > +Do not propagate MDWE protection to child processes on
>
> Should this mention that PR_MDWE_NO_INHERIT requires
> PR_MDWE_REFUSE_EXEC_GAIN (unless I forgot how this was supposed to
> work).

Yes! :) That's a good point, thank you Catalin