** Changed in: linux (Ubuntu Bionic)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1768630
Title:
arm64 SDEI support needs trampoline code for KPTI
Status in linux package in Ubuntu:
In Progress
Status in linux source package in Bionic:
Fix Committed
Bug description:
[Impact]
In bug 1756096, we backported SDEI (Software Delegated Exception Interface)
support for arm64. However, this backport missed 2 changes that make the SDEI
entry point a trampoline which make sure the kernel is mapped before
processing. (The kernel may not be mapped if KPTI is enabled and the exception
comes in while e.g. executing in usermode). This may lead to a crash.
[Test Case]
I haven't yet found a way to inject/simulate an SDEI, so I can only
regression test by boot testing.
[Regression Risk]
The code is restricted to arm64, and should only run on systems that support
SDEI. I'm unaware of any production firmware that expose the SDEI ACPI table,
which means this code isn't actively used yet anyway.
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