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

[lijiang]

Hi,

After applied this patch, i made a test on the following machines. It works well.

[a] HPE ProLiant DL385 Gen10 (878612-B21) AMD EPYC 7251 8-Core Processor

[b] Dell PowerEdge R7425 AMD EPYC 7401 24-Core Processor

[c] AMD Speedway AMD Eng Sample: 2S1405A3VIHF4_28/14_N

[d] AMD Ethanol X AMD Eng Sample: 2S1402E2VJUG2_20/14_N

On the [a] machine, it works well in the crashkernel=160M case, but need
to remove the CONFIG_DEBUG_INFO from .config, otherwise it could happen the
OOM. And it also works well in all >= 256M(crashkernel) cases(no need to
remove the above option from .config).

On the [b][c][d] machine, it also works fine in the crashkernel=256M cases,
also need to remove the debug info, otherwise it could happen the OOM. And
it also works well in all >= 320M(crashkernel) cases.

Thanks.


Tested-by: Lianbo Jiang <lijiang@xxxxxxxxxx>


å 2019å06æ12æ 21:32, Lendacky, Thomas åé:
> The SME workarea used during early encryption of the kernel during boot
> is situated on a 2MB boundary after the end of the kernel text, data,
> etc. sections (_end).  This works well during initial boot of a compressed
> kernel because of the relocation used for decompression of the kernel.
> But when performing a kexec boot, there's a chance that the SME workarea
> may not be mapped by the kexec pagetables or that some of the other data
> used by kexec could exist in this range.
> 
> Create a section for SME in the vmlinux.lds.S.  Position it after "_end"
> so that the memory will be reclaimed during boot and, since it is all
> zeroes, it compresses well.  Since this new section will be part of the
> kernel, kexec will account for it in pagetable mappings and placement of
> data after the kernel.
> 
> Here's an example of a kernel size without and with the SME section:
> 	without:
> 		vmlinux:	36,501,616
> 		bzImage:	 6,497,344
> 
> 		100000000-47f37ffff : System RAM
> 		  1e4000000-1e47677d4 : Kernel code	(0x7677d4)
> 		  1e47677d5-1e4e2e0bf : Kernel data	(0x6c68ea)
> 		  1e5074000-1e5372fff : Kernel bss	(0x2fefff)
> 
> 	with:
> 		vmlinux:	44,419,408
> 		bzImage:	 6,503,136
> 
> 		880000000-c7ff7ffff : System RAM
> 		  8cf000000-8cf7677d4 : Kernel code	(0x7677d4)
> 		  8cf7677d5-8cfe2e0bf : Kernel data	(0x6c68ea)
> 		  8d0074000-8d0372fff : Kernel bss	(0x2fefff)
> 
> Cc: Baoquan He <bhe@xxxxxxxxxx>
> Cc: Lianbo Jiang <lijiang@xxxxxxxxxx>
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  arch/x86/kernel/vmlinux.lds.S      | 16 ++++++++++++++++
>  arch/x86/mm/mem_encrypt_identity.c | 22 ++++++++++++++++++++--
>  2 files changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> index 0850b5149345..8c4377983e54 100644
> --- a/arch/x86/kernel/vmlinux.lds.S
> +++ b/arch/x86/kernel/vmlinux.lds.S
> @@ -379,6 +379,22 @@ 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. Resides
> +	 * on a 2MB boundary to simplify the pagetable setup used for
> +	 * the encryption.
> +	 */
> +	. = ALIGN(HPAGE_SIZE);
> +	.sme : AT(ADDR(.sme) - LOAD_OFFSET) {
> +		__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
> + * avoid any possibility of boot parameters or initramfs images being
> + * placed such that the in-place encryption logic overwrites them.  This
> + * section is 2MB aligned to allow for simple pagetable setup using only
> + * PMD entries (see vmlinux.lds.S).
> + */
> +static char sme_workarea[2 * PMD_PAGE_SIZE] __section(.sme);
> +
>  static char sme_cmdline_arg[] __initdata = "mem_encrypt";
>  static char sme_cmdline_on[]  __initdata = "on";
>  static char sme_cmdline_off[] __initdata = "off";
> @@ -314,8 +327,13 @@ void __init sme_encrypt_kernel(struct boot_params *bp)
>  	}
>  #endif
>  
> -	/* Set the encryption workarea to be immediately after the kernel */
> -	workarea_start = kernel_end;
> +	/*
> +	 * We're running identity mapped, so we must obtain the address to the
> +	 * SME encryption workarea using rip-relative addressing.
> +	 */
> +	asm ("lea sme_workarea(%%rip), %0"
> +	     : "=r" (workarea_start)
> +	     : "p" (sme_workarea));
>  
>  	/*
>  	 * Calculate required number of workarea bytes needed:
>