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Revision as of 14:57, 28 April 2020 by Jlinton (talk | contribs) (Initial PAC+BTI request)
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Change Proposal Name Aarch64 Pointer Authentication & Branch Target Enablement


Arm Pointer Authentication (PAC) is a method of hardening code from Return Oriented Programming (ROP) attacks. It uses a tag in a pointer to sign and verify pointers. Branch Target Identification (BTI) is another code hardening method, where the branch/jump target is identified with a special landing pad instruction. Outside of some system support in glibc+kernel, packages gain the additional hardening by compiling with the -mbranch-protection= flag available in recent versions of GCC. In particular -mbranch-protection=standard enables both BTI and PAC, with backwards compatible to armv8.0 code sequences that activate on v8.2 (PAC) & v8.4 (BTI) enabled Arm machines.


Current status

  • Targeted release: Fedora 33
  • Last updated: 2020-04-28
  • FESCo issue: <will be assigned by the Wrangler>
  • Tracker bug: <will be assigned by the Wrangler>
  • Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

Benefit to Fedora

PAC & BTI are code hardening features, they should serve to make fedora more resistant to a couple further classes of runtime attacks. By enabling this early fedora is once again proven to be at the leading edge of security and linux development. If everything works as planned, this change will be invisible to the end user, except in cases where the applications will trap behaviour that appears to be caused by exploit attempts.


  • Proposal owners:

Work with individual package maintainers in the case of build failures or runtime exceptions. In the latter case there are two possibilities. First on v8.0 hardware, which is currently the most common, the additional instruction sequences are treated as NOP's and should be completely ignored by the hardware. It may be possible on v8.2/8.4 hardware that PAC or BTI may need additional tweaks for hand written assembly which interacts with PAC/BTI enabled code.

  • Other developers:

Assure their packages continue to compile and pass unit/integration/etc tests on v8.0 hardware. Continue to monitor runtime problems on v8.2+ for bugs, vs exploit attempts.

  • Policies and guidelines: N/A (not a System Wide Change)
  • Trademark approval: N/A (not needed for this Change)

Upgrade/compatibility impact

N/A (not a System Wide Change)

How To Test

N/A (not a System Wide Change)

User Experience


N/A (not a System Wide Change)

Contingency Plan

  • Contingency mechanism: (What to do? Who will do it?) N/A (not a System Wide Change)
  • Contingency deadline: N/A (not a System Wide Change)
  • Blocks release? N/A (not a System Wide Change), Yes/No
  • Blocks product? product


N/A (not a System Wide Change)

Release Notes