linux-kernel - Re: x86/efi: Make efi_set_virtual_address

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Date:   Thu, 29 Jun 2023 23:45:13 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Niklāvs Koļesņikovs 
        <pinkflames.linux@...il.com>, linux-efi@...r.kernel.org,
        x86@...nel.org, regressions@...ts.linux.dev
Subject: Re: x86/efi: Make efi_set_virtual_address_map IBT safe

On Thu, Jun 29 2023 at 23:42, Ard Biesheuvel wrote:
> On Thu, 29 Jun 2023 at 21:35, Thomas Gleixner <tglx@...utronix.de> wrote:
>> Niklāvs reported a boot regression on an Alderlake machine and bisected it
>> to commit 9df9d2f0471b ("init: Invoke arch_cpu_finalize_init() earlier").
>>
>> By moving the invocation of arch_cpu_finalize_init() further down he
>> identified that efi_enter_virtual_mode() is the function which causes
>> the boot hang.
>>
>> The main difference of the earlier invocation is that the boot CPU is
>> already fully initialized and mitigations and alternatives are applied.
>>
>> But the only really interesting change turned out to be IBT, which is
>> now enabled before efi_enter_virtual_mode(). "ibt=off" on the kernel
>> command line cured the problem.
>>
>> Inspection of the involved calls in efi_enter_virtual_mode() unearthed that
>> efi_set_virtual_address_map() is the only place in the kernel which invokes
>> an EFI call without the IBT safe wrapper. This went obviously unnoticed so
>> far as IBT was enabled later.
>>
>> Use arch_efi_call_virt() instead of efi_call() to cure that.
>>
>> Fixes: fe379fa4d199 ("x86/ibt: Disable IBT around firmware")
>> Fixes: 9df9d2f0471b ("init: Invoke arch_cpu_finalize_init() earlier")
>> Reported-by: Niklāvs Koļesņikovs <pinkflames.linux@...il.com>
>> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217602
>
> Reviewed-by: Ard Biesheuvel <ardb@...nel.org>
>
> I take it you'll send this straight to Linus?

I can do that.

Thanks,

        tglx