Re: [PATCH v2 1/5] x86: Update x86 low level version check of microcode

[Fouad Hilly <fouad.hilly@xxxxxxxxx>]

On Mon, Apr 22, 2024 at 3:09 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>
> On 16.04.2024 11:15, Fouad Hilly wrote:
> > Update microcode version check at Intel and AMD Level by:
> > Preventing the low level code from sending errors if the microcode
> > version provided is not a newer version.
>
> And why is this change (a) wanted and (b) correct?
I will improve the message description to cover more details and reasoning.
>
> > Other errors will be sent like before.
> > When the provided microcode version is the same as the current one, code
> > to point to microcode provided.
>
> I'm afraid I can't interpret this sentence.
"provided" is the firmware presented\provided to the code for firmware
flashing. As above, I will provide more comprehensive description.
>
> > Microcode version check happens at higher and common level in core.c.
> > Keep all the required code at low level that checks for signature and CPU 
> > compatibility
> >
> > [v2]
> > Update message description to better describe the changes
>
> This belongs ...
>
> > Signed-off-by: Fouad Hilly <fouad.hilly@xxxxxxxxx>
> > ---
>
> ... below the separator.
>
> > --- a/xen/arch/x86/cpu/microcode/amd.c
> > +++ b/xen/arch/x86/cpu/microcode/amd.c
> > @@ -383,12 +383,8 @@ static struct microcode_patch *cf_check 
> > cpu_request_microcode(
> >                  goto skip;
> >              }
> >
> > -            /*
> > -             * If the new ucode covers current CPU, compare ucodes and 
> > store the
> > -             * one with higher revision.
> > -             */
> > -            if ( (microcode_fits(mc->patch) != MIS_UCODE) &&
> > -                 (!saved || (compare_header(mc->patch, saved) == 
> > NEW_UCODE)) )
> > +            /* If the provided ucode covers current CPU, then store its 
> > revision. */
> > +            if ( (microcode_fits(mc->patch) != MIS_UCODE) && !saved )
> >              {
> >                  saved = mc->patch;
> >                  saved_size = mc->len;
> > --- a/xen/arch/x86/cpu/microcode/intel.c
> > +++ b/xen/arch/x86/cpu/microcode/intel.c
> > @@ -294,8 +294,7 @@ static int cf_check apply_microcode(const struct 
> > microcode_patch *patch)
> >
> >      result = microcode_update_match(patch);
> >
> > -    if ( result != NEW_UCODE &&
> > -         !(opt_ucode_allow_same && result == SAME_UCODE) )
> > +    if ( result != NEW_UCODE && result != SAME_UCODE )
> >          return -EINVAL;
>
> Unlike the other two adjustments this one results in still permitting
> only same-or-newer. How does this fit with the AMD change above and
> the other Intel change ...
To be fixed in V3
>
> > @@ -354,12 +353,8 @@ static struct microcode_patch *cf_check 
> > cpu_request_microcode(
> >          if ( error )
> >              break;
> >
> > -        /*
> > -         * If the new update covers current CPU, compare updates and store 
> > the
> > -         * one with higher revision.
> > -         */
> > -        if ( (microcode_update_match(mc) != MIS_UCODE) &&
> > -             (!saved || compare_revisions(saved->rev, mc->rev) == 
> > NEW_UCODE) )
> > +        /* If the provided ucode covers current CPU, then store its 
> > revision. */
> > +        if ( (microcode_update_match(mc) != MIS_UCODE) && !saved )
> >              saved = mc;
>
> ... here?
I assume this refers to the previous comment? Which will be fixed in V3
>
> Jan

Thanks,

Fouad