Re: [PATCH v3 13/26] x86/virt/seamldr: Allocate and populate a module update request

[Chao Gao]

On Wed, Jan 28, 2026 at 12:03:25PM +0800, Huang, Kai wrote:
>
>> +/*
>> + * Allocate and populate a seamldr_params.
>> + * Note that both @module and @sig should be vmalloc'd memory.
>
>Nit:
>
>How about actually using is_vmalloc_addr() to check in the code rather than
>documenting in the comment?
>
>I see you have already checked the overall 'data' buffer is vmalloc()'ed in
>seamldr_install_module() so the 'module' and 'sig' (part of 'data') must be
>too.  But since is_vmalloc_addr() is cheap so I think it's also fine to do
>the check here.  We can also WARN() so it can be used to catch bug.

Kai,

Thanks a lot.

Looks good to me. I think WARN() is always better than comments.

>> +	if (!verify_checksum(blob)) {
>> +		pr_err("invalid checksum\n");
>> +		return ERR_PTR(-EINVAL);
>> +	}
>> +
>> +	return alloc_seamldr_params(module, module_size, sig, sig_size);
>> +}
>
>It's weird that we have do verify checksum manually, because hardware
>normally catches that.
>
>I suppose this is because we want to catch as many errors as possible before
>actually asking P-SEAMLDR to do module update, since in order to do which we
>have to shutdown the existing module first and there's no returning point
>once we reach that?

Yes. Exactly.

>
>If so a comment would be helpful.

Will do.

>
>Also, it's also weird that you have to write code for checksum on your own.
>I guess the kernel should already have some library code for that.
>
>I checked and it _seems_ the code in lib/checksum.c could be used?
>
>I am not expert though, but I think we should use kernel lib code when we
>can.

Good point. After a quick review, lib/checksum.c uses a different algorithm
than tdx_blob's checksum. It adds the carry bit to the checksum, while tdx_blob
drops the carry bit.

*sigh* when I designed the checksum algorithm, I wasn't aware of lib/checksum.c.