[RFC] Adjust kern.usrstack sysctl by stack gap.
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Authored by dgr_semihalf.com on Aug 26 2021, 1:57 PM.

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mw
emaste
imp
kib
cy

Summary

kern.usrstack sysctl is used by some programs (e.g. firefox) when
creating threads. This sysctl returns hardcoded value. When stack
gap is enabled, the stack is instead moved by a random amount of
bytes. This can cause those programs to crash.

Adjust kern.usrstack value by the size of stack gap. This fixes the
issue with firefox not starting with stack gap enabled.

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dgr_semihalf.com requested review of this revision.Aug 26 2021, 1:57 PM

dgr_semihalf.com created this revision.

This requires D31516.

Another approach would be to leave this sysctl as is and instead create a new one which could be used to read the actual stack position with stack gap enabled.

dgr_semihalf.com added a parent revision: D31516: setrlimit: Take stack gap into account..Aug 26 2021, 2:04 PM

2khramtsov_gmail.com added a subscriber: 2khramtsov_gmail.com.Aug 28 2021, 9:03 PM

This does address the firefox and thunderbird segfaults.

dgr_semihalf.com mentioned this in D31516: setrlimit: Take stack gap into account..Sep 2 2021, 8:13 AM

No, this is not going to work. Problem is that the same sysctl is used by programs to get _other_ processes stack address, in particular pstrings location.

Abandoning this, I created D31897 and D31898, which add a different sysctl and modify libthr to use it.

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sys/

kern/

kern_exec.c

10 lines

Diff 94235

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sys/kern/kern_exec.c

This file contains generated code, which does not normally need to be reviewed. Show File Contents

[RFC] Adjust kern.usrstack sysctl by stack gap.AbandonedPublicActions