linux-kernel - Re: [PATCH v1 2/2] acpi, x86: Remove encryption mask from ACPI page protection type

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Message-ID: <20170727073904.iay5jclhhjnqhyib@gmail.com>
Date:   Thu, 27 Jul 2017 09:39:04 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dave Young <dyoung@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v1 2/2] acpi, x86: Remove encryption mask from ACPI page
 protection type


* Tom Lendacky <thomas.lendacky@....com> wrote:

> The function arch_apei_get_mem_attributes() is used to set the page
> protection type for ACPI physical addresses. When SME is active, the
> associated protection type needs to not have the encryption mask set
> since the ACPI tables live in un-encrypted memory. Modify the
> arch_apei_get_mem_attributes() function to remove the encryption mask
> when SME is active by returning the PAGE_KERNEL_IO protection type.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/include/asm/acpi.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/acpi.h b/arch/x86/include/asm/acpi.h
> index 562286f..89df39d 100644
> --- a/arch/x86/include/asm/acpi.h
> +++ b/arch/x86/include/asm/acpi.h
> @@ -34,6 +34,7 @@
>  
>  #ifdef CONFIG_ACPI_APEI
>  # include <asm/pgtable_types.h>
> +# include <linux/mem_encrypt.h>
>  #endif
>  
>  #ifdef CONFIG_ACPI
> @@ -164,8 +165,12 @@ static inline pgprot_t arch_apei_get_mem_attribute(phys_addr_t addr)
>  	 * anything other than PAGE_KERNEL (some arm64 platforms
>  	 * require the equivalent of PAGE_KERNEL_NOCACHE), return that
>  	 * until we know differently.
> +	 *
> +	 * When SME is active, the ACPI information will not reside in
> +	 * in memory in an encrypted state so return a protection attribute
> +	 * that does not have the encryption bit set.
>  	 */
> -	 return PAGE_KERNEL;
> +	 return sme_active() ? PAGE_KERNEL_IO : PAGE_KERNEL;

'in in memory'?

Also, this seems a bit ad-hoc to me. What are the rules for what is encrypted and 
what is not?

I presume the main rule is that everything that was written before the kernel 
activates SME, and which the kernel will read later on, is unencrypted - 
everything else is encrypted. Is that correct?

How about things like kexec creating a separate mptable for the kexec kernel - 
would that code have to create unencrypted data? See 
e820__memblock_alloc_reserved() and related code.

Thanks,

	Ingo