Re: [PATCH v1 1/1] x86/fred: Remove ENDBR64 from FRED entry points

[Xin Li <xin@zytor.com>]

On 7/15/2025 1:40 AM, Peter Zijlstra wrote:
> On Mon, Jul 14, 2025 at 11:50:57PM -0700, Xin Li wrote:
>> On 7/14/2025 11:44 PM, Xin Li (Intel) wrote:
>>> The FRED specification v9.0 states that there is no need for FRED
>>> event handlers to begin with ENDBR64, because in the presence of
>>> supervisor indirect branch tracking, FRED event delivery does not
>>> enter the WAIT_FOR_ENDBRANCH state.
>>>
>>> As a result, remove ENDBR64 from FRED entry points.
>>>
>>> Then add ANNOTATE_NOENDBR to indicate that FRED entry points will
>>> never be used for indirect calls to suppress an objtool warning.
>>>
>>> This change implies that any indirect CALL/JMP to FRED entry points
>>> causes #CP in the presence of supervisor indirect branch tracking.
>>>
>>> Credit goes to Jennifer Miller<jmill@asu.edu> and other contributors
>>> from Arizona State University whose work led to this change.
>>>
>>> Link:https://lore.kernel.org/linux-hardening/Z60NwR4w%2F28Z7XUa@ubun/
>>> Reviewed-by: H. Peter Anvin (Intel)<hpa@zytor.com>
>>> Signed-off-by: Xin Li (Intel)<xin@zytor.com>
>>> Cc: Jennifer Miller<jmill@asu.edu>
>>> Cc: Peter Zijlstra<peterz@infradead.org>
>>> Cc: Andrew Cooper<andrew.cooper3@citrix.com>
>>> Cc: H. Peter Anvin<hpa@zytor.com>
>> Sorry, forgot to put CC stable.
> Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
> 
> Right?

You bet!

Will send v2 to address it soon.