linux-kernel - Re: [PATCH v8 32/40] x86/compressed: use firmware-validated CPUID for SEV-SNP guests

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Message-ID: <YelTDp4gsEyscWTI@zn.tnic>
Date:   Thu, 20 Jan 2022 13:18:22 +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>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v8 32/40] x86/compressed: use firmware-validated CPUID
 for SEV-SNP guests

On Fri, Dec 10, 2021 at 09:43:24AM -0600, Brijesh Singh wrote:
> Subject: Re: [PATCH v8 32/40] x86/compressed: use firmware-validated CPUID for SEV-SNP guests
									    ^
									    leafs

or so.

> From: Michael Roth <michael.roth@....com>
> 
> SEV-SNP guests will be provided the location of special 'secrets'
> 'CPUID' pages via the Confidential Computing blob. This blob is
> provided to the boot kernel either through an EFI config table entry,
> or via a setup_data structure as defined by the Linux Boot Protocol.
> 
> Locate the Confidential Computing from these sources and, if found,
> use the provided CPUID page/table address to create a copy that the
> boot kernel will use when servicing cpuid instructions via a #VC

CPUID

> handler.
> 
> Signed-off-by: Michael Roth <michael.roth@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/boot/compressed/sev.c | 13 ++++++++++
>  arch/x86/include/asm/sev.h     |  1 +
>  arch/x86/kernel/sev-shared.c   | 43 ++++++++++++++++++++++++++++++++++
>  3 files changed, 57 insertions(+)
> 
> diff --git a/arch/x86/boot/compressed/sev.c b/arch/x86/boot/compressed/sev.c
> index 93e125da12cf..29dfb34b5907 100644
> --- a/arch/x86/boot/compressed/sev.c
> +++ b/arch/x86/boot/compressed/sev.c
> @@ -415,6 +415,19 @@ bool snp_init(struct boot_params *bp)
>  	if (!cc_info)
>  		return false;
>  
> +	/*
> +	 * If SEV-SNP-specific Confidential Computing blob is present, then
	     ^
	     a


> +	 * firmware/bootloader have indicated SEV-SNP support. Verifying this
> +	 * involves CPUID checks which will be more reliable if the SEV-SNP
> +	 * CPUID table is used. See comments for snp_cpuid_info_create() for

s/for/over/ ?

> +	 * more details.
> +	 */
> +	snp_cpuid_info_create(cc_info);
> +
> +	/* SEV-SNP CPUID table should be set up now. */
> +	if (!snp_cpuid_active())
> +		sev_es_terminate(1, GHCB_TERM_CPUID);

Right, that is not needed now.

>  	 * Pass run-time kernel a pointer to CC info via boot_params so EFI
>  	 * config table doesn't need to be searched again during early startup
> diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
> index cd189c20bcc4..4fa7ca20d7c9 100644
> --- a/arch/x86/include/asm/sev.h
> +++ b/arch/x86/include/asm/sev.h
> @@ -157,6 +157,7 @@ bool snp_init(struct boot_params *bp);
>   * sev-shared.c via #include and these declarations can be dropped.
>   */
>  struct cc_blob_sev_info *snp_find_cc_blob_setup_data(struct boot_params *bp);
> +void snp_cpuid_info_create(const struct cc_blob_sev_info *cc_info);
>  #else
>  static inline void sev_es_ist_enter(struct pt_regs *regs) { }
>  static inline void sev_es_ist_exit(void) { }
> diff --git a/arch/x86/kernel/sev-shared.c b/arch/x86/kernel/sev-shared.c
> index bd58a4ce29c8..5cb8f87df4b3 100644
> --- a/arch/x86/kernel/sev-shared.c
> +++ b/arch/x86/kernel/sev-shared.c
> @@ -403,6 +403,23 @@ snp_cpuid_find_validated_func(u32 func, u32 subfunc, u32 *eax, u32 *ebx,
>  	return false;
>  }
>  
> +static void __init snp_cpuid_set_ranges(void)
> +{
> +	const struct snp_cpuid_info *cpuid_info = snp_cpuid_info_get_ptr();
> +	int i;
> +
> +	for (i = 0; i < cpuid_info->count; i++) {
> +		const struct snp_cpuid_fn *fn = &cpuid_info->fn[i];
> +
> +		if (fn->eax_in == 0x0)
> +			cpuid_std_range_max = fn->eax;
> +		else if (fn->eax_in == 0x40000000)
> +			cpuid_hyp_range_max = fn->eax;
> +		else if (fn->eax_in == 0x80000000)
> +			cpuid_ext_range_max = fn->eax;
> +	}
> +}

Kinda arbitrary to have a separate function which has a single caller.
You can just as well move the loop into snp_cpuid_info_create() and put
a comment above it:

	/* Set CPUID ranges. */
	for (i = 0; i < cpuid_info->count; i++) {
		...

Also, snp_cpuid_info_create() should be called snp_setup_cpuid_table()
which is what this thing does.

Thx.

-- 
Regards/Gruss,
    Boris.

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