[DragonFlyBSD - Submit #2299] (Closed) Prevent mapping to page 0 on pc32

bugtracker-admin at leaf.dragonflybsd.org bugtracker-admin at leaf.dragonflybsd.org
Thu Aug 19 12:40:45 PDT 2021

Issue #2299 has been updated by dillon.

Description updated
Status changed from New to Closed

We're cleaning up the bug database.  I think I'm going to close this particular report for a few reasons.  First, we do not want to disallow mmap()ings at address 0 per-say, its just that the default is to not put anything there in order to catch common null pointer indirection bugs.  Actually disallowing such mappings can lead to issues with interpreters and other special-purpose applications.

For kernel accesses, modern CPUs have support to fault on accesses to userspace from kernel mode so that is not a pressing issue either.

I like the idea of the user address limits being sysctl'd, but there aren't any practical use cases.  Since we are maximal in that regard, there also aren't any potential portability issues either.  So I think... if someone really wanted to they could submit a quick patch for user access to such limits.  For the kernel, defined constants are ideal due to miscellaneous calculations made with them.


Submit #2299: Prevent mapping to page 0 on pc32

* Author: logan1
* Status: Closed
* Priority: Normal
* Target version: 6.2
* Start date: 2012-02-04
OpenBSD prevents mapping to page 0 to prevent certain
class of exploits.

It has been reported that it can break Wine.

I tested it on pc32.

Feedback welcomed.

vmparam.diff (1.71 KB)

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