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

[Mario Limonciello <superm1@kernel.org>]

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.