Re: [PATCH v7 0/8] x86/kexec: Add exception handling for relocate_kernel

[Ingo Molnar]

* David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote:

> On Thu, 2025-03-13 at 19:58 +0000, David Woodhouse wrote:
> > 
> > Reproduced that by going back to x86-64 defconfig. 
> 
> Turns out the unret check doesn't even run unless CONFIG_DEBUG_ENTRY is
> enabled (which enables CONFIG_NOINSTR_VALIDATION and thus runs objtool
> on vmlinux.o). Which is why I didn't see it.
> 
> > vmlinux.o: warning: objtool: exc_handler+0xe: early indirect call
> 
> With Peter's help (thanks), this is fixed by adding VALIDATE_UNRET_END.
> I'll squash this into the next posting:
> 
> --- a/arch/x86/kernel/relocate_kernel_64.S
> +++ b/arch/x86/kernel/relocate_kernel_64.S
> @@ -481,6 +481,9 @@ SYM_CODE_START_NOALIGN(kexec_debug_exc_vectors)
>  SYM_CODE_END(kexec_debug_exc_vectors)
>  
>  SYM_CODE_START_LOCAL_NOALIGN(exc_handler)
> +       /* No need for ret mitigations during kexec */
> +       VALIDATE_UNRET_END
> +
>         pushq   %rax
>         pushq   %rbx
>         pushq   %rcx

Great!

I've applied patch #1 back to tip:x86/boot.

I've skipped the -v7 versions of patch #2 and #3 because AFAICS you've 
changed exc_handler already, so a backmerge of this annotation fix 
wouldn't be enough.

Thanks,

	Ingo