Re: [PATCH v7 36/36] x86/mm: Add support to make use of Secure Memory Encryption

[Borislav Petkov]

On Fri, Jun 16, 2017 at 01:56:39PM -0500, Tom Lendacky wrote:
> Add support to check if SME has been enabled and if memory encryption
> should be activated (checking of command line option based on the
> configuration of the default state).  If memory encryption is to be
> activated, then the encryption mask is set and the kernel is encrypted
> "in place."
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> ---
>  arch/x86/include/asm/mem_encrypt.h |    6 ++-
>  arch/x86/kernel/head64.c           |    4 +-
>  arch/x86/mm/mem_encrypt.c          |   86 +++++++++++++++++++++++++++++++++++-
>  3 files changed, 90 insertions(+), 6 deletions(-)

...

> +/*
> + * Some SME functions run very early causing issues with the stack-protector
> + * support. Provide a way to turn off this support on a per-function basis.
> + */
> +#define SME_NOSTACKP __attribute__((__optimize__("no-stack-protector")))

__nostackp

just like the others in include/linux/compiler-gcc.h.

> +
> +static char sme_cmdline_arg[] __initdata = "mem_encrypt";
> +static char sme_cmdline_on[]  __initdata = "on";
> +static char sme_cmdline_off[] __initdata = "off";
>  
>  /*
>   * Since SME related variables are set early in the boot process they must
> @@ -200,6 +215,8 @@ void __init mem_encrypt_init(void)
>  
>  	/* Call into SWIOTLB to update the SWIOTLB DMA buffers */
>  	swiotlb_update_mem_attributes();
> +
> +	pr_info("AMD Secure Memory Encryption (SME) active\n");
>  }
>  
>  void swiotlb_set_mem_attributes(void *vaddr, unsigned long size)
> @@ -527,8 +544,73 @@ void __init sme_encrypt_kernel(void)
>  	native_write_cr3(__native_read_cr3());
>  }
>  
> -void __init sme_enable(void)
> +void __init SME_NOSTACKP sme_enable(struct boot_params *bp)
>  {
> +	const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
> +	unsigned int eax, ebx, ecx, edx;
> +	bool active_by_default;
> +	unsigned long me_mask;
> +	char buffer[16];
> +	u64 msr;
> +
> +	/* Check for the SME support leaf */
> +	eax = 0x80000000;
> +	ecx = 0;
> +	native_cpuid(&eax, &ebx, &ecx, &edx);
> +	if (eax < 0x8000001f)
> +		return;
> +
> +	/*
> +	 * Check for the SME feature:
> +	 *   CPUID Fn8000_001F[EAX] - Bit 0
> +	 *     Secure Memory Encryption support
> +	 *   CPUID Fn8000_001F[EBX] - Bits 5:0
> +	 *     Pagetable bit position used to indicate encryption
> +	 */
> +	eax = 0x8000001f;
> +	ecx = 0;
> +	native_cpuid(&eax, &ebx, &ecx, &edx);
> +	if (!(eax & 1))
> +		return;
> +
> +	me_mask = 1UL << (ebx & 0x3f);
> +
> +	/* Check if SME is enabled */
> +	msr = __rdmsr(MSR_K8_SYSCFG);
> +	if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
> +		return;
> +
> +	/*
> +	 * Fixups have not been applied to phys_base yet and we're running
> +	 * identity mapped, so we must obtain the address to the SME command
> +	 * line argument data using rip-relative addressing.
> +	 */
> +	asm ("lea sme_cmdline_arg(%%rip), %0"
> +	     : "=r" (cmdline_arg)
> +	     : "p" (sme_cmdline_arg));
> +	asm ("lea sme_cmdline_on(%%rip), %0"
> +	     : "=r" (cmdline_on)
> +	     : "p" (sme_cmdline_on));
> +	asm ("lea sme_cmdline_off(%%rip), %0"
> +	     : "=r" (cmdline_off)
> +	     : "p" (sme_cmdline_off));
> +
> +	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
> +		active_by_default = true;
> +	else
> +		active_by_default = false;
> +
> +	cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr |
> +				     ((u64)bp->ext_cmd_line_ptr << 32));
> +
> +	cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer));
> +
> +	if (strncmp(buffer, cmdline_on, sizeof(buffer)) == 0)

	if (!strncmp(...

> +		sme_me_mask = me_mask;
> +	else if (strncmp(buffer, cmdline_off, sizeof(buffer)) == 0)

	else if (!strncmp(...

-- 
Regards/Gruss,
    Boris.

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