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Bug 1847148 - Aarch64 Pointer Authentication & Branch Target Enablement
Summary: Aarch64 Pointer Authentication & Branch Target Enablement
Alias: None
Product: Fedora
Classification: Fedora
Component: Changes Tracking
Version: 33
Hardware: Unspecified
OS: Unspecified
Target Milestone: ---
Assignee: Jeremy Linton
QA Contact:
Depends On: 1861423 1862110
Blocks: ARMTracker F33Changes
TreeView+ depends on / blocked
Reported: 2020-06-15 19:03 UTC by Ben Cotton
Modified: 2020-10-27 14:47 UTC (History)
4 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Last Closed: 2020-10-27 14:47:56 UTC
Type: ---

Attachments (Terms of Use)

Description Ben Cotton 2020-06-15 19:03:43 UTC
This is a tracking bug for Change: Aarch64 Pointer Authentication & Branch Target Enablement
For more details, see:

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 v8.3 (PAC) & v8.5 (BTI) enabled Arm machines.

Comment 1 Jeremy Linton 2020-07-14 15:35:21 UTC
We should hold off on getting the flag in until gcc 10.2 lands as there are a couple PAC fixes in 10.2 we will want.

Comment 2 Jeremy Linton 2020-07-17 21:15:44 UTC
I went with the KISS method, and just added it to the optflags. The pull request is here:

There is a build here:

The gcc bug that should be integrated before the mass rebuild is:

The fix has been backported to gcc 9/10.1 and is in the 10.2 branch as well. 

Its not clear to me if fedora is planning on moving to 10.2 before the rebuild, otherwise I can create a PR for the 10.1 backport.

Comment 3 Florian Weimer 2020-07-24 07:22:00 UTC
As far as I can tell, this change requires special builds of gcc and glibc:

As a result, the mass rebuild will NOT complete this change.

Comment 4 Jeremy Linton 2020-07-28 17:54:42 UTC
I've checked with Szabolcs, and its his understanding too that simply building gcc with mbranch-protection=standard will do what we want.

Comment 5 Ben Cotton 2020-08-11 14:42:31 UTC
Branching F33 Change Tracker bugs.

Today is the code complete (testable) deadline. All bugs should be at least in MODIFIED state by now to indicate they are testable.

Comment 6 Jeremy Linton 2020-08-13 16:57:24 UTC
Large parts of this are in place, I need to test/validate functionality, but I think the distro has definitely been "modified" so that is my error for not setting the bz state.

Comment 7 Ben Cotton 2020-08-27 01:12:00 UTC
Yesterday we reached the Code complete (100% code complete) deadline for Fedora 33 Changes. If your Change is complete, please set this tracking bug to ON_QA. If you need to defer this Change to Fedora 34, please let NEEDINFO me.

As a reminder, we are now in the Beta Freeze. If you need to land package updates, please propose it as a Freeze Exception at

Comment 8 Jeremy Linton (ARM) 2020-09-08 22:12:39 UTC
I've been testing this on a v8.0 machine (honeycomb, rpi4) as well as a v8.5 model, and everything looks reasonable at the moment.

Comment 9 Ben Cotton 2020-10-27 14:47:56 UTC
Closing tracking bugs for F33. If your change didn't make it into F33 for some reason, please reopen this and NEEDINFO me.

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