Re: [PATCH 04/22] x86/srso: Fix SBPB enablement for spec_rstack_overflow=off

From: Borislav Petkov
Date: Mon Aug 21 2023 - 10:17:05 EST


On Sun, Aug 20, 2023 at 06:19:01PM -0700, Josh Poimboeuf wrote:
> If the user has requested no SRSO mitigation, other mitigations can use
> the lighter-weight SBPB instead of IBPB.
>
> Fixes: fb3bd914b3ec ("x86/srso: Add a Speculative RAS Overflow mitigation")
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> ---
> arch/x86/kernel/cpu/bugs.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index b0ae985aa6a4..10499bcd4e39 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -2433,7 +2433,7 @@ static void __init srso_select_mitigation(void)
>
> switch (srso_cmd) {
> case SRSO_CMD_OFF:
> - return;
> + goto pred_cmd;

Can't do that - you need to synchronize it with retbleed. If retbleed
has selected IBPB mitigation you must not override it.

It's a whole different story whether it makes sense.

Thx.

--
Regards/Gruss,
Boris.

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