Re: [PATCH v5 09/16] x86/bugs: Allow retbleed=stuff only on Intel

Borislav Petkov
2025-04-27T15:37:59Z

On Fri, Apr 18, 2025 at 11:17:14AM -0500, David Kaplan wrote:
> The retbleed=stuff mitigation is only applicable for Intel CPUs affected
> by retbleed. If this option is selected for another vendor, print a
> warning and fall back to the AUTO option.
>
> Signed-off-by: David Kaplan <david.kaplan@amd.com>
> ---
> arch/x86/kernel/cpu/bugs.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index 72e04938fdcb..84d3f6b3d1eb 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -1187,6 +1187,10 @@ static void __init retbleed_select_mitigation(void)
> case RETBLEED_CMD_STUFF:
> if (IS_ENABLED(CONFIG_MITIGATION_CALL_DEPTH_TRACKING) &&
> spectre_v2_enabled == SPECTRE_V2_RETPOLINE) {
> + if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
> + pr_err("WARNING: retbleed=stuff only supported for Intel CPUs.\n");
> + goto do_cmd_auto;
> + }

Right, the reason it is possible to select this mitigation on other
vendors is purely to be able to experiment with the different mitigation
techniques.

But I've never considered that ability to be particularly useful - and
even if, if you wanna do that, you might as well hack the kernel too.

So yeah, I guess it is better to not allow non-sensical mitigations.

Thx.

--
Regards/Gruss,
Boris.