linux-kernel - Re: [PATCH v9 24/43] x86/compressed/acpi: Move EFI detection to helper

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Date:   Thu, 3 Feb 2022 15:39:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        brijesh.ksingh@...il.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v9 24/43] x86/compressed/acpi: Move EFI detection to
 helper

On Fri, Jan 28, 2022 at 11:17:45AM -0600, Brijesh Singh wrote:
> diff --git a/arch/x86/boot/compressed/efi.c b/arch/x86/boot/compressed/efi.c
> new file mode 100644
> index 000000000000..daa73efdc7a5
> --- /dev/null
> +++ b/arch/x86/boot/compressed/efi.c
> @@ -0,0 +1,50 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Helpers for early access to EFI configuration table.
> + *
> + * Originally derived from arch/x86/boot/compressed/acpi.c
> + */
> +
> +#include "misc.h"
> +#include <linux/efi.h>
> +#include <asm/efi.h>

Yap, it is includes like that which cause this whole decompressor
include hell. One day...

> +
> +/**
> + * efi_get_type - Given boot_params, determine the type of EFI environment.
> + *
> + * @boot_params:        pointer to boot_params
> + *
> + * Return: EFI_TYPE_{32,64} for valid EFI environments, EFI_TYPE_NONE otherwise.
> + */
> +enum efi_type efi_get_type(struct boot_params *boot_params)

				struct boot_params *bp

> +{
> +	struct efi_info *ei;
> +	enum efi_type et;
> +	const char *sig;
> +
> +	ei = &boot_params->efi_info;
> +	sig = (char *)&ei->efi_loader_signature;
> +
> +	if (!strncmp(sig, EFI64_LOADER_SIGNATURE, 4)) {
> +		et = EFI_TYPE_64;
> +	} else if (!strncmp(sig, EFI32_LOADER_SIGNATURE, 4)) {
> +		et = EFI_TYPE_32;
> +	} else {
> +		debug_putstr("No EFI environment detected.\n");
> +		et = EFI_TYPE_NONE;
> +	}
> +
> +#ifndef CONFIG_X86_64
> +	/*
> +	 * Existing callers like acpi.c treat this case as an indicator to
> +	 * fall-through to non-EFI, rather than an error, so maintain that
> +	 * functionality here as well.
> +	 */
> +	if (ei->efi_systab_hi || ei->efi_memmap_hi) {
> +		debug_putstr("EFI system table is located above 4GB and cannot be accessed.\n");
> +		et = EFI_TYPE_NONE;
> +	}
> +#endif
> +
> +	return et;
> +}
> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> index 01cc13c12059..a26244c0fe01 100644
> --- a/arch/x86/boot/compressed/misc.h
> +++ b/arch/x86/boot/compressed/misc.h
> @@ -176,4 +176,20 @@ void boot_stage2_vc(void);
>  
>  unsigned long sev_verify_cbit(unsigned long cr3);
>  
> +enum efi_type {
> +	EFI_TYPE_64,
> +	EFI_TYPE_32,
> +	EFI_TYPE_NONE,
> +};

Haha, EFI folks will be wondering where in the spec that thing is... :-)))

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette