linux-kernel - Re: [PATCH] efi/x86: use naked RET on mixed mode call wrapper

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Message-ID: <YtWqit2B3UYIWht1@zn.tnic>
Date:   Mon, 18 Jul 2022 20:46:34 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        stable <stable@...r.kernel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>
Subject: Re: [PATCH] efi/x86: use naked RET on mixed mode call wrapper

On Mon, Jul 18, 2022 at 11:34:02AM -0700, Linus Torvalds wrote:
> Why would we have to protect the kernel from EFI?

Yes, we cleared this up on IRC in the meantime.

This was raised as a concern in case we don't trust EFI. But we cannot
not (double negation on purpose) trust EFI because it can do whatever it
likes anyway, "underneath" the OS.

I'm keeping the UNTRAIN_RET-in-C diff in my patches/ folder, though - I
get the feeling we might need it soon for something else.

:-)

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH
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