linux-kernel - Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for memory encryption

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Date:   Tue, 6 Sep 2016 11:31:13 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for
 memory encryption

On Mon, Aug 22, 2016 at 05:36:46PM -0500, Tom Lendacky wrote:
> Adding general kernel support for memory encryption includes:
> - Modify and create some page table macros to include the Secure Memory
>   Encryption (SME) memory encryption mask
> - Update kernel boot support to call an SME routine that checks for and
>   sets the SME capability (the SME routine will grow later and for now
>   is just a stub routine)
> - Update kernel boot support to call an SME routine that encrypts the
>   kernel (the SME routine will grow later and for now is just a stub
>   routine)
> - Provide an SME initialization routine to update the protection map with
>   the memory encryption mask so that it is used by default
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>

...

> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 54a2372..88c7bae 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -28,6 +28,7 @@
>  #include <asm/bootparam_utils.h>
>  #include <asm/microcode.h>
>  #include <asm/kasan.h>
> +#include <asm/mem_encrypt.h>
>  
>  /*
>   * Manage page tables very early on.
> @@ -42,7 +43,7 @@ static void __init reset_early_page_tables(void)
>  {
>  	memset(early_level4_pgt, 0, sizeof(pgd_t)*(PTRS_PER_PGD-1));
>  	next_early_pgt = 0;
> -	write_cr3(__pa_nodebug(early_level4_pgt));
> +	write_cr3(__sme_pa_nodebug(early_level4_pgt));
>  }
>  
>  /* Create a new PMD entry */
> @@ -54,7 +55,7 @@ int __init early_make_pgtable(unsigned long address)
>  	pmdval_t pmd, *pmd_p;
>  
>  	/* Invalid address or early pgt is done ?  */
> -	if (physaddr >= MAXMEM || read_cr3() != __pa_nodebug(early_level4_pgt))
> +	if (physaddr >= MAXMEM || read_cr3() != __sme_pa_nodebug(early_level4_pgt))
>  		return -1;
>  
>  again:
> @@ -157,6 +158,11 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>  
>  	clear_page(init_level4_pgt);
>  
> +	/* Update the early_pmd_flags with the memory encryption mask */
> +	early_pmd_flags |= _PAGE_ENC;
> +
> +	sme_early_init();
> +

So maybe this comes later but you're setting _PAGE_ENC unconditionally
*before* sme_early_init().

I think you should set it in sme_early_init() and iff SME is enabled.

-- 
Regards/Gruss,
    Boris.

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