linux-kernel - Re: [Part1 PATCH v4 02/17] x86/mm: Add Secure Encrypted Virtualization (SEV) support

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Date:   Sun, 17 Sep 2017 16:02:06 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [Part1 PATCH v4 02/17] x86/mm: Add Secure Encrypted
 Virtualization (SEV) support

On Sat, Sep 16, 2017 at 07:34:03AM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> Provide support for Secure Encrypted Virtualization (SEV). This initial
> support defines a flag that is used by the kernel to determine if it is
> running with SEV active.
> 
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: linux-kernel@...r.kernel.org
> Cc: x86@...nel.org
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/include/asm/mem_encrypt.h |  6 ++++++
>  arch/x86/mm/mem_encrypt.c          | 26 ++++++++++++++++++++++++++
>  include/linux/mem_encrypt.h        | 12 ++++++++----
>  3 files changed, 40 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 6a77c63540f7..2b024741bce9 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -47,6 +47,9 @@ void __init mem_encrypt_init(void);
>  
>  void swiotlb_set_mem_attributes(void *vaddr, unsigned long size);
>  
> +bool sme_active(void);
> +bool sev_active(void);
> +
>  #else	/* !CONFIG_AMD_MEM_ENCRYPT */
>  
>  #define sme_me_mask	0ULL
> @@ -64,6 +67,9 @@ static inline void __init sme_early_init(void) { }
>  static inline void __init sme_encrypt_kernel(void) { }
>  static inline void __init sme_enable(struct boot_params *bp) { }
>  
> +static inline bool sme_active(void) { return false; }
> +static inline bool sev_active(void) { return false; }
> +
>  #endif	/* CONFIG_AMD_MEM_ENCRYPT */
>  
>  /*
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 3fcc8e01683b..4e6dcabe52fc 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -40,6 +40,8 @@ static char sme_cmdline_off[] __initdata = "off";
>  u64 sme_me_mask __section(.data) = 0;
>  EXPORT_SYMBOL_GPL(sme_me_mask);
>  
> +unsigned int sev_enabled __section(.data) = 0;

static.

> +
>  /* Buffer used for early in-place encryption by BSP, no locking needed */
>  static char sme_early_buffer[PAGE_SIZE] __aligned(PAGE_SIZE);
>  
> @@ -190,6 +192,30 @@ void __init sme_early_init(void)
>  		protection_map[i] = pgprot_encrypted(protection_map[i]);
>  }
>  
> +/*
> + * SME and SEV are very similar but they are not the same, so there are
> + * times that the kernel will need to distinguish between SME and SEV. The
> + * sme_active() and sev_active() functions are used for this.  When a
> + * distinction isn't needed, the mem_encrypt_active() function can be used.
> + *
> + * The trampoline code is a good example for this requirement.  Before
> + * paging is activated, SME will access all memory as decrypted, but SEV
> + * will access all memory as encrypted.  So, when APs are being brought
> + * up under SME the trampoline area cannot be encrypted, whereas under SEV
> + * the trampoline area must be encrypted.
> + */

Good!

> +bool sme_active(void)
> +{
> +	return sme_me_mask && !sev_enabled;
> +}
> +EXPORT_SYMBOL_GPL(sme_active);
> +
> +bool sev_active(void)
> +{
> +	return sme_me_mask && sev_enabled;
> +}
> +EXPORT_SYMBOL_GPL(sev_active);
> +
>  /* Architecture __weak replacement functions */
>  void __init mem_encrypt_init(void)
>  {
> diff --git a/include/linux/mem_encrypt.h b/include/linux/mem_encrypt.h
> index 265a9cd21cb4..b55ba30a60a0 100644
> --- a/include/linux/mem_encrypt.h
> +++ b/include/linux/mem_encrypt.h
> @@ -22,17 +22,21 @@
>  #else	/* !CONFIG_ARCH_HAS_MEM_ENCRYPT */
>  
>  #define sme_me_mask	0ULL
> +#define sev_enabled	0
> +
> +static inline bool sme_active(void) { return false; }
> +static inline bool sev_active(void) { return false; }
>  
>  #endif	/* CONFIG_ARCH_HAS_MEM_ENCRYPT */
>  
> -static inline bool sme_active(void)
> +static inline unsigned long sme_get_me_mask(void)
>  {
> -	return !!sme_me_mask;
> +	return sme_me_mask;

Same issue as before: if we're going to export the mask, you don't
need the accessor. If we're going to hide the mask in a static in
mem_encrypt.c, we should use the accessor solely.

But that can be done ontop of the patchset.

> -static inline u64 sme_get_me_mask(void)
> +static inline bool mem_encrypt_active(void)
>  {
> -	return sme_me_mask;
> +	return !!sme_me_mask;

As before, you don't need the !!.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--