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Differential D19514

KPTI: add control from proccontrol(8)
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Authored by kib on Mar 8 2019, 8:32 PM.
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Subscribers
andrew
bdragon
delphij
gordon
imp
jhibbits
pho
rpokala

Details

Reviewers
emaste
jhb
markj
manu
Commits
rS345229: proccontrol(1): Add kpti control mode.
rS345228: amd64 KPTI: add control from procctl(2).
rS345227: amd64: Add md process flags and first P_MD_PTI flag.
rS345226: amd64: fix switching to the pmap with pti disabled.
rS345225: amd64: rewrite cpu_switch.S fragment to reload tss.rsp0 on context switch.
Summary

The change consists of four:

  • when the pmap with pti disabled (i.e. pm_ucr3 == PMAP_NO_CR3) is activated, tss.rsp0 was not updated. Any interrupt that happen before context switch would use pti trampoline stack for hardware frame but fault handlers are not prepared to this. Correctly update tss.rsp0 for both PMAP_NO_CR3 and pti pmaps. Since the code now duplicates the asm in cpu_switch.S, remove the fragment to update tss.rsp0 from there.
  • addition of P_MD_KPTI flag, this is autonomous and probably should be committed unconditionally. The flag controls if the new pmap after exec gets KPTI active.
  • addition of procctl(2) MD stuff (this is not complete since it lacks stubs on anything non-amd64).
  • addition of procctl(2) and proccontrol(8) knobs for KPTI.

Diff Detail

Repository
rS FreeBSD src repository - subversion
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Build Status
Buildable 22964

Event Timeline

kib created this revision.Mar 8 2019, 8:32 PM
Herald added subscribers: rpokala, imp. · View Herald TranscriptMar 8 2019, 8:32 PM
Harbormaster completed remote builds in B22959: Diff 54848.Mar 8 2019, 8:32 PM
kib updated this revision to Diff 54850.Mar 8 2019, 8:47 PM

Remove unneeded proctree lock acquisition.

Noted by: mjg

Harbormaster completed remote builds in B22961: Diff 54850.Mar 8 2019, 8:47 PM
kib updated this revision to Diff 54851.Mar 8 2019, 8:55 PM

Switch to pget(), simplify control flow.

Harbormaster completed remote builds in B22962: Diff 54851.Mar 8 2019, 8:55 PM
jhb added a comment.Mar 8 2019, 8:57 PM

This generally looks good to me. Presumably for MFC'ing we'd have to stick the md_flags field at the end of 'struct proc' instead.

sys/sys/procctl.h
65

I would probably put the #include earlier in the file to match the style in other headers?

kib updated this revision to Diff 54854.EditedMar 8 2019, 9:13 PM
kib marked an inline comment as done.

Move machine/procctl.h header inclusion up.

Harbormaster completed remote builds in B22964: Diff 54854.Mar 8 2019, 9:13 PM
markj added inline comments.Mar 8 2019, 9:18 PM
sys/amd64/include/proc.h
73

Does cpu_fork() need to initialize the flags in the child?

kib added inline comments.Mar 8 2019, 9:34 PM
sys/amd64/amd64/vm_machdep.c
186

Markj, look at this line.

markj accepted this revision.Mar 9 2019, 1:53 AM
This revision is now accepted and ready to land.Mar 9 2019, 1:53 AM
jhb accepted this revision.Mar 11 2019, 10:48 PM
emaste added subscribers: gordon, delphij.Mar 12 2019, 5:53 PM
kib updated this revision to Diff 54993.Mar 12 2019, 6:26 PM

Use PRIV_IO for proccontrol(KPTI_CTL) instead of PRIV_KMEM_READ. The later is more true, but we do grant this privilege to non-root users on basis that /dev/kmem permission should be used.

Fix nasty bug with handling of PMAP_NO_CR3 thread in pti-enabled environment. I will explain it in updated revision summary since I need it for commit message (shortly, tss.rsp0 was not updated on activation from exec).

This revision now requires review to proceed.Mar 12 2019, 6:26 PM
Harbormaster completed remote builds in B23046: Diff 54993.Mar 12 2019, 6:26 PM
kib edited the summary of this revision. (Show Details)Mar 12 2019, 6:29 PM
kib edited the summary of this revision. (Show Details)
kib updated this revision to Diff 54994.Mar 12 2019, 6:46 PM

I was wrong removing the bits to update tss.rsp0 in the context switch asm. If thread uses non-common TSS, then we need to update newly switched TSS' tss.rsp0 as well. While there, rewrite this fragment to avoid jumps.

Harbormaster completed remote builds in B23047: Diff 54994.Mar 12 2019, 6:46 PM
kib added a subscriber: pho.Mar 13 2019, 1:26 PM
kib added a comment.Mar 13 2019, 1:30 PM

Peter, could you, please, test this ?

The updated proccontrol(1) allows to disable or enable KPTI for future execve(2) of the process and its children. So for instance you can start one batch of stress2 normally, and another using the command like

proccontrol -m kpti -s disable sh <script>

This would make two stress2 runs running in parallel, one with KPTI enabled, another disabled. You can, of course, run a specific program under enabled/disabled mode as well.
It would be most important to check the ldt and io ports tests.

markj accepted this revision.Mar 13 2019, 8:03 PM
This revision is now accepted and ready to land.Mar 13 2019, 8:03 PM
kib updated this revision to Diff 55066.Mar 14 2019, 5:00 PM

Fill missed bits for !amd64 architectures.

This revision now requires review to proceed.Mar 14 2019, 5:00 PM
Herald added a reviewer: manu. · View Herald TranscriptMar 14 2019, 5:00 PM
Herald added subscribers: bdragon, jhibbits, andrew. · View Herald Transcript
Harbormaster completed remote builds in B23089: Diff 55066.Mar 14 2019, 5:00 PM
This revision was not accepted when it landed; it landed in state Needs Review.Mar 16 2019, 11:12 AM
Closed by commit rS345225: amd64: rewrite cpu_switch.S fragment to reload tss.rsp0 on context switch. (authored by kib). · Explain Why
This revision was automatically updated to reflect the committed changes.

Revision Contents
Changeset List

PathSize
sys/
amd64/
amd64/
9 lines
71 lines
include/
6 lines
6 lines
compat/
freebsd32/
4 lines
i386/
include/
6 lines
kern/
3 lines
4 lines
2 lines
sys/
3 lines
4 lines
x86/
include/
43 lines
usr.bin/
proccontrol/
35 lines

Diff 54854

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sys/amd64/amd64/pmap.c

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sys/amd64/amd64/vm_machdep.c

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sys/amd64/include/proc.h

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sys/amd64/include/procctl.h

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sys/compat/freebsd32/freebsd32_misc.c

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sys/i386/include/procctl.h

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sys/kern/kern_exec.c

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sys/kern/kern_procctl.c

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sys/kern/kern_thread.c

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sys/sys/proc.h

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sys/sys/procctl.h

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sys/x86/include/procctl.h

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usr.bin/proccontrol/proccontrol.c

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