** Changed in: linux-azure (Ubuntu Eoan)
Status: In Progress => Fix Committed
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https://bugs.launchpad.net/bugs/1877425
Title:
linux-azure: Enable FSGSBASE instructions to support SGX
Status in linux-azure package in Ubuntu:
In Progress
Status in linux-azure-4.15 package in Ubuntu:
In Progress
Status in linux-azure source package in Bionic:
Invalid
Status in linux-azure-4.15 source package in Bionic:
In Progress
Status in linux-azure source package in Eoan:
Fix Committed
Status in linux-azure-4.15 source package in Eoan:
Invalid
Status in linux-azure source package in Focal:
In Progress
Status in linux-azure-4.15 source package in Focal:
Invalid
Bug description:
X86 has instructions (RDFSBASE, RDGSBASE, WRFSBASE, and WRGSBASE) to
support read/write of the FS/GS bases. Linux doesn't allow user mode
code to execute these instructions by default. These instructions can
be enabled for user mode by setting the 16th control bit of the CR4
register. Since only protected mode can modify the control registers,
application programs and operating-system procedures (running at
privilege levels 1, 2, or 3) are prevented from reading or loading the
control registers. The kernel patch sets this CR4 register and handles
the context switching to account for the fact that user mode can now
modify the FS/GS base.
A recent news article that talks about the performance benefits:
https://phoronix.com/scan.php?page=news_item&px=Intel-FSGSBASE-
Linux-2020. Another news article covers the performance information in
a lot more detail by running a number of performance tests:
https://www.phoronix.com/scan.php?page=article&item=linux-wip-
fsgsbase&num=1
Patch set: https://lkml.org/lkml/2019/10/4/725
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