linux-kernel - Re: [PATCH v3 02/19] x86/boot: Move mem_encrypt= parsing to the decompressor

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Message-ID: <CAMj1kXG9W0XeEVR4tXDDg0Ai9XPsZGrTJaSRYUqgTV-xtFxjdQ@mail.gmail.com>
Date: Wed, 31 Jan 2024 10:12:13 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Ard Biesheuvel <ardb+git@...gle.com>, linux-kernel@...r.kernel.org, 
	Kevin Loughlin <kevinloughlin@...gle.com>, Tom Lendacky <thomas.lendacky@....com>, 
	Dionna Glaze <dionnaglaze@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Andy Lutomirski <luto@...nel.org>, Arnd Bergmann <arnd@...db.de>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Kees Cook <keescook@...omium.org>, Brian Gerst <brgerst@...il.com>, linux-arch@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [PATCH v3 02/19] x86/boot: Move mem_encrypt= parsing to the decompressor

On Wed, Jan 31, 2024 at 9:35 AM Borislav Petkov <bp@...en8.de> wrote:
>
> On Mon, Jan 29, 2024 at 07:05:05PM +0100, Ard Biesheuvel wrote:
> > +/*
> > + * Set the memory encryption xloadflag based on the mem_encrypt= command line
> > + * parameter, if provided. If not, the consumer of the flag decides what the
> > + * default behavior should be.
> > + */
> > +static void set_mem_encrypt_flag(struct setup_header *hdr)
>
> parse_mem_encrypt
>

OK

> > +{
> > +     hdr->xloadflags &= ~(XLF_MEM_ENCRYPTION | XLF_MEM_ENCRYPTION_ENABLED);
> > +
> > +     if (IS_ENABLED(CONFIG_ARCH_HAS_MEM_ENCRYPT)) {
>
> That's unconditionally enabled on x86:
>
>         select ARCH_HAS_MEM_ENCRYPT
>
> in x86/Kconfig.
>
> Which sounds like you need a single XLF_MEM_ENCRYPT and simplify this
> more.
>

OK, but that only means I can drop the if().

The reason we need two flags is because there is no default value to
use when the command line param is absent.

There is CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT but that one is AMD
specific. There is CONFIG_X86_MEM_ENCRYPT which is shared between
SME/SEV and TDX, which has no default setting.

> > +             int on = cmdline_find_option_bool("mem_encrypt=on");
> > +             int off = cmdline_find_option_bool("mem_encrypt=off");
> > +
> > +             if (on || off)
> > +                     hdr->xloadflags |= XLF_MEM_ENCRYPTION;
> > +             if (on > off)
> > +                     hdr->xloadflags |= XLF_MEM_ENCRYPTION_ENABLED;
> > +     }
> > +}
>
> Otherwise, I like the simplification.
>

Cheers.