Re: [PATCH v5 5/5] x86/CPU/AMD: Print AGESA string from DMI additional information entry

[Mario Limonciello]

On 3/15/26 3:56 PM, Borislav Petkov wrote:
> On Sun, Mar 15, 2026 at 10:14:48AM -0500, Mario Limonciello wrote:
> > FYI - you're replying to the v5 not the v6 [1].
>
> Whoops, sorry about that.
>
> It looks I've still used the right set tho:
>
> v6_20260307_superm1_print_agesa_version_at_bootup.mbx
>
> :)
>
> > I did add a check for info->count < 1, but that's not what you were actually
> > looking for.  Do you have a suggestion for an upper limit to bound things?
> >
> > I was thinking something like this:
> >
> > #define DMI_LIMIT 10
> > int limit = info -> count > DMI_LIMIT ? DMI_LIMIT : info->count;
> > end  = (void *)info + limit * info->header.length;
>
> So that Zen5 laptop here says:
>
> [    0.853836] dmi_scan_additional: next: 0xffffc9000051950c, end: 0xffffc90000519515, hdr length: 14
> [    0.854364] entry 0: length: 9
> [    0.854576] AGESA: StrixPI-FP8 1.0.0.1d
>
> So after that first loop pass we have
>
> 	next = 0xffffc9000051950c + 9 = 0xffffc90000519515
>
> And we should terminate. So I guess that's not a lot of entries.
>
> In terms of limiting, I'd do something like:
>
> /* A generous max size for the additional DMI entries */
> #define MAX_DMI_ADDITIONAL_ENTRIES_LEN		256
>
> 	if (info->header.length > MAX_DMI_ADDITIONAL_ENTRIES_LEN)
> 		info->header.length = MAX_DMI_ADDITIONAL_ENTRIES_LEN;
>
> And now you have a sane upper limit and we don't rely on any numbers the BIOS
> is telling us.
>
> Thx.

But that can't actually happen.  info->header.length is u8.

So we're never going to end up with that many entries such that it would 
exhaust the check.