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Differential D26894

mmap(2): Document guard size and related EINVAL.
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Authored by kib on Oct 21 2020, 5:48 PM.
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alc
markj
emaste
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rS366918: mmap(2): Document guard size for MAP_STACK and related EINVAL.
Summary

Based on submission by: emaste

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rS FreeBSD src repository - subversion
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Event Timeline

kib created this revision.Oct 21 2020, 5:48 PM
Herald added a subscriber: imp. · View Herald TranscriptOct 21 2020, 5:48 PM
kib requested review of this revision.Oct 21 2020, 5:48 PM
Harbormaster completed remote builds in B34307: Diff 78559.Oct 21 2020, 5:48 PM
emaste accepted this revision.Oct 21 2020, 6:30 PM
emaste added inline comments.
lib/libc/sys/mmap.2
354 ↗(On Diff #78559)

The size of the guard, in pages, ...

460 ↗(On Diff #78559)

less than or equal to

This revision is now accepted and ready to land.Oct 21 2020, 6:30 PM
kib updated this revision to Diff 78560.Oct 21 2020, 6:37 PM
kib marked 2 inline comments as done.

Handle Ed' notes.
Use .Dv for sysctl mib name.
Bump date.

This revision now requires review to proceed.Oct 21 2020, 6:37 PM
Harbormaster completed remote builds in B34308: Diff 78560.Oct 21 2020, 6:37 PM
emaste accepted this revision.Oct 21 2020, 6:57 PM
This revision is now accepted and ready to land.Oct 21 2020, 6:57 PM
markj added inline comments.Oct 21 2020, 7:04 PM
lib/libc/sys/mmap.2
456 ↗(On Diff #78560)

Didn't the mailing list report mention ENOMEM?

markj accepted this revision.Oct 21 2020, 7:21 PM
markj added inline comments.
lib/libc/sys/mmap.2
456 ↗(On Diff #78560)

Sorry, I did not read the full thread.

Closed by commit rS366918: mmap(2): Document guard size for MAP_STACK and related EINVAL. (authored by kib). · Explain WhyOct 21 2020, 9:40 PM
This revision was automatically updated to reflect the committed changes.
kib added a commit: rS366918: mmap(2): Document guard size for MAP_STACK and related EINVAL..
alc added inline comments.Oct 22 2020, 6:16 PM
head/lib/libc/sys/mmap.2
354–355

IMHO, we should be explicitly saying that the guard is carved out the specified stack size, reducing the effective size of the stack. Right now, I could infer that from reading the errors section, but I argue that I shouldn't have to infer it.

emaste added inline comments.Oct 22 2020, 6:45 PM
head/lib/libc/sys/mmap.2
354–355

good point, how's this:

Index: lib/libc/sys/mmap.2
===================================================================
--- lib/libc/sys/mmap.2 (revision 366945)
+++ lib/libc/sys/mmap.2 (working copy)
@@ -353,6 +353,8 @@
 stacks can grow without requiring mapping the whole stack in advance.
 The size of the guard, in pages, is specified by sysctl
 .Dv security.bsd.stack_guard_page .
+The guard region is placed at the starting address of the allocation,
+and the usable stack is reduced by the size of the guard.
 .El
 .Pp
 The
emaste added a comment.Oct 22 2020, 6:47 PM

Oh I see @kib has D26908 for this.

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head/lib/libc/sys/mmap.2

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