Re: FAILED: patch "[PATCH] x86/retbleed: Fix return thunk alignment" failed to apply to 5.15-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, May 13, 2023 at 12:21:07PM +0200, Borislav Petkov wrote:
> On Sat, May 13, 2023 at 05:17:13PM +0900, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 5.15-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> > 
> > To reproduce the conflict and resubmit, you may use the following commands:
> > 
> > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
> > git checkout FETCH_HEAD
> > git cherry-pick -x 9a48d604672220545d209e9996c2a1edbb5637f6
> > # <resolve conflicts, build, test, etc.>
> > git commit -s
> > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2023051313-wrangle-brick-b43d@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
> > 
> > Possible dependencies:
> > 
> > 9a48d6046722 ("x86/retbleed: Fix return thunk alignment")
> > a149180fbcf3 ("x86: Add magic AMD return-thunk")
> > d9e9d2300681 ("x86,objtool: Create .return_sites")
> > 15e67227c49a ("x86: Undo return-thunk damage")
> > 0b53c374b9ef ("x86/retpoline: Use -mfunction-return")
> > 369ae6ffc41a ("x86/retpoline: Cleanup some #ifdefery")
> > a883d624aed4 ("x86/cpufeatures: Move RETPOLINE flags to word 11")
> > 22922deae13f ("Merge tag 'objtool-core-2022-05-23' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")
> 
> Right, so that looks like this:
> 
> The patch which causes the misalignment is
> 
> c4691712b546 ("x86/linkage: Add ENDBR to SYM_FUNC_START*()")
> 
> which came in 5.18 (v5.17-rc8-21-gc4691712b546) and the one which adds
> the actual untraining sequence:
> 
> a149180fbcf3 ("x86: Add magic AMD return-thunk")
> 
> came in 5.19.
> 
> So adding a Fixes: tag pointing to a patch which goes before the actual
> patch didn't make any sense to me last night.
> 
> HOWEVER, Thadeu did backport it here as
> 
> a9c0926fc754 ("x86: Add magic AMD return-thunk")
> 
> but the other patch wasn't backported.
> 
> So the 5.15 build looks good:
> 
> ffffffff81c01f7f <zen_untrain_ret>:
> ffffffff81c01f7f:       f6                      .byte 0xf6
> 
> ffffffff81c01f80 <__x86_return_thunk>:
> ffffffff81c01f80:       c3                      ret
> ffffffff81c01f81:       cc                      int3
> ffffffff81c01f82:       0f ae e8                lfence
> ffffffff81c01f85:       eb f9                   jmp    ffffffff81c01f80 <__x86_return_thunk>
> ffffffff81c01f87:       cc                      int3
> 
> So 5.15 doesn't need it.

Great, thanks for looking into this, much appreciated.

greg k-h