Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1477217 > unrolled thread

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

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for  memory encryption Borislav Petkov <bp@alien8.de> - 2016-09-06 11:30 +0200
    Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for  memory encryption Borislav Petkov <bp@alien8.de> - 2016-09-07 18:00 +0200
      Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for  memory encryption Borislav Petkov <bp@alien8.de> - 2016-09-08 16:00 +0200

#1477217 — 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@amd.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.

ECO tip #101: Trim your mails when you reply.

[toc] | [next] | [standalone]

#1478453

On Wed, Sep 07, 2016 at 09:30:54AM -0500, Tom Lendacky wrote:
> _PAGE_ENC is #defined as sme_me_mask and sme_me_mask has already been
> set (or not set) at this point - so it will be the mask if SME is
> active or 0 if SME is not active.

Yeah, I remember :-)

> sme_early_init() is merely propagating the mask to other structures.
> Since early_pmd_flags is mainly used in this file (one line in
> head_64.S is the other place) I felt it best to modify it here. But it
> can always be moved if you feel that is best.

Hmm, so would it work then if you stick it in early_pmd_flags'
definition like you do with the other masks? I.e.,

pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE | _PAGE_ENC & ~(_PAGE_GLOBAL | _PAGE_NX);

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

[toc] | [prev] | [next] | [standalone]

#1479244

On Thu, Sep 08, 2016 at 08:26:27AM -0500, Tom Lendacky wrote:
> When does this value get initialized?  Since _PAGE_ENC is #defined to
> sme_me_mask, which is not set until the boot process begins, I'm afraid
> we'd end up using the initial value of sme_me_mask, which is zero.  Do
> I have that right?

Hmm, but then that would hold true for all the other defines where you
OR-in _PAGE_ENC, no?

In any case, the preprocessed source looks like this:

pmdval_t early_pmd_flags = (((((((pteval_t)(1)) << 0) | (((pteval_t)(1)) << 1) | (((pteval_t)(1)) << 6) | (((pteval_t)(1)) << 5) | (((pteval_t)(1)) << 8)) | (((pteval_t)(1)) << 63)) | (((pteval_t)(1)) << 7)) | sme_me_mask) & ~((((pteval_t)(1)) << 8) | (((pteval_t)(1)) << 63));

but the problem is later, when building:

arch/x86/kernel/head64.c:39:28: error: initializer element is not constant
 pmdval_t early_pmd_flags = (__PAGE_KERNEL_LARGE | _PAGE_ENC) & ~(_PAGE_GLOBAL | _PAGE_NX);
                            ^
scripts/Makefile.build:153: recipe for target 'arch/x86/kernel/head64.s' failed

so I guess not. :-\

Ok, then at least please put the early_pmd_flags init after
sme_early_init() along with a small comment explaning what happens.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web