Re: [PATCH v9 00/22] Enable FRED with KVM VMX

[Andrew Cooper]

On 05/05/2026 9:20 pm, Maciej Wieczor-Retman wrote:
> On 2026-05-05 at 19:30:21 +0100, Andrew Cooper wrote:
>> On 05/05/2026 7:04 pm, Maciej Wieczor-Retman wrote:
>>
>>> I think you'd need to add another check in vmx_inject_exception() to handle that
>>> DB_VECTOR too. Simply changing the event type if the vector is of DB_VECTOR type
>>> fixes that problem but then the selftest fails in other places (assert
>>> fred_handler_called and saved rip vs expected_rip). I didn't yet have the time
>>> to figure out what could be wrong there, maybe you would have more of an idea :)
>> #DB is intercepted to mitigate CVE-2015-8104 (systemwide DoS).  But, to
>> start with, check that the test passes when #DB is not intercepted. 
>> That's the basecase for architectural behaviour.
> I take it you mean dropping the ICEBP selftest test case and just checking INT3
> and INT $0x20? In that case the other two tests pass after a minor change -
> namely in guest_code() the expected_rip needs to be volatile as well. Otherwise
> there is a RIP mismatch.
>
> Or did you mean I should check something else?

The selftest is correct AIUI.  You should be able to prove this by
disabling #DB interception, and observing the test to pass.

Then, there's a logic bug to fix to cause the test to pass even when #DB
interception is active (which is necessary due to CVE-2015-8104).

~Andrew