Re: [PATCH v4 6/6] x86/virt/tdx: Re-initialize the extensions on runtime TDX module update

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] tdx: use stale features0 metadata for TDH.EXT.INIT during update
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commit b9612f7aae2064bfaded9e7d4ac02af4fa76ac04
Author: Xu Yilun <yilun.xu@linux.intel.com>

x86/virt/tdx: Re-initialize the extensions on runtime TDX module update
    
Runtime TDX module update introduces a mechanism to update the module
firmware while preserving and restoring TDX operations. The extensions
functionalities should also be re-initialized as part of the restoration
process.

> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index f1cc0422d129a..4cce77b6a31f6 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c

[ ... ]

> @@ -1384,6 +1384,19 @@ static __init int init_tdx_module_extensions(void)
>  	return tdx_ext_init();
>  }
>  
> +/*
> + * Don't update the memory requirement metadata or try memory allocation in
> + * stop_machine(). If an incompatible update requires more memory, let the
> + * extensions re-initialization fail.
> + */
> +static int reinit_tdx_module_extensions(void)
> +{
> +	if (!(tdx_sysinfo.features.tdx_features0 & TDX_FEATURES0_EXT))
> +		return 0;
> +
> +	return tdx_ext_init();
> +}

[Severity: High]
Does this use stale features0 metadata during the update?

If an administrator applies a valid TDX firmware update that changes the
presence of zero-memory extensions, could relying on the boot-time cached
value of tdx_sysinfo.features.tdx_features0 cause problems?

If the update introduces zero-memory extensions to a module that originally
had none, the cached flag evaluates to 0, skipping TDH.EXT.INIT. According
to the TDX architecture, this could leave the new TDX module stuck in the
SYS_UPDATED state.

Conversely, if an update removes extensions, the cached flag remains 1,
causing the kernel to erroneously call TDH.EXT.INIT on a module that
doesn't support it.

Should the kernel read the updated TDX_FEATURES0 metadata field using
read_sys_metadata_field() during the update instead of relying on the
boot-time cached value?

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Sashiko AI review · https://sashiko.dev/#/patchset/20261013-tdx-module-ext-v4-0-de5ffac65470@linux.intel.com?part=6