Re: [PATCH v2 2/2] x86/mm: Create an SME workarea in the kernel for early encryption

[Borislav Petkov]

On Fri, Jun 14, 2019 at 09:15:19PM +0000, Lendacky, Thomas wrote:
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index ca2252ca6ad7..a7aa65b44c71 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -387,6 +387,30 @@ SECTIONS
>  	. = ALIGN(PAGE_SIZE);		/* keep VO_INIT_SIZE page aligned */
>  	_end = .;
>  
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +	/*
> +	 * SME workarea section: Lives outside of the kernel proper (_text -
> +	 * _end) for performing in-place encryption of the kernel during boot.
> +	 *
> +	 * Resides after _end because even though the .brk section is after
> +	 * __end_of_kernel_reserve, the .brk section is later reserved as a
> +	 * part of the kernel. It is used in very early boot code and not
> +	 * needed after that, so it is located after __end_of_kernel_reserve
> +	 * so that it will be discarded and become part of the available
> +	 * memory.
> +	 *
> +	 * Resides on a 2MB boundary to simplify the pagetable setup used for
> +	 * the encryption.
> +	 */
> +	. = ALIGN(HPAGE_SIZE);
> +	.sme : AT(ADDR(.sme) - LOAD_OFFSET) {

Should we call that section something more generic as

	.early_scratch

or so?

Someone else might need something like that too, in the future...

Also, the DISCARDS sections do get freed at runtime so why not make it
part of the DISCARD section...?

> +		__sme_begin = .;
> +		*(.sme)
> +		. = ALIGN(HPAGE_SIZE);
> +		__sme_end = .;
> +	}
> +#endif
> +
>  	STABS_DEBUG
>  	DWARF_DEBUG
>  
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index 4aa9b1480866..c55c2ec8fb12 100644
> --- a/arch/x86/mm/mem_encrypt_identity.c
> +++ b/arch/x86/mm/mem_encrypt_identity.c
> @@ -73,6 +73,19 @@ struct sme_populate_pgd_data {
>  	unsigned long vaddr_end;
>  };
>  
> +/*
> + * This work area lives in the .sme section, which lives outside of
> + * the kernel proper. It is sized to hold the intermediate copy buffer
> + * and more than enough pagetable pages.
> + *
> + * By using this section, the kernel can be encrypted in place and we

replace that "we" with an impartial passive formulation.

Other than that, I like the commenting, very helpful!

Thx.

-- 
Regards/Gruss,
    Boris.

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