On Fri, 2020-05-15 at 19:53 -0700, Yu-cheng Yu wrote:

On Fri, 2020-05-15 at 16:56 -0700, Dave Hansen wrote:

quoted

On 5/15/20 4:29 PM, Yu-cheng Yu wrote:

quoted

[...]
I have run them with CET enabled.  All of them pass, except for the following:
Sigreturn from 64-bit to 32-bit fails, because shadow stack is at a 64-bit
address.  This is understandable.

[...]
One a separate topic: You ran the selftests and one failed.  This is a
*MASSIVE* warning sign.  It should minimally be described in your cover
letter, and accompanied by a fix to the test case.  It is absolutely
unacceptable to introduce a kernel feature that causes a test to fail.
You must either fix your kernel feature or you fix the test.

This code can not be accepted until this selftests issue is rectified.

The x86/sigreturn test constructs 32-bit ldt entries, and does sigreturn from
64-bit to 32-bit context.  We do not have a way to construct a static 32-bit
shadow stack.  Why do we want that?  I think we can simply run the test with CET
disabled.

Yu-cheng