Re: [PATCH v5 32/32] x86/mm: Add support to make use of Secure Memory Encryption

[Borislav Petkov]

On Tue, Apr 18, 2017 at 04:22:23PM -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/kernel/head_64.S |    1 +
>  arch/x86/mm/mem_encrypt.c |   83 +++++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 80 insertions(+), 4 deletions(-)

...

> +unsigned long __init sme_enable(struct boot_params *bp)
>  {
> +	const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
> +	unsigned int eax, ebx, ecx, edx;
> +	unsigned long me_mask;
> +	bool active_by_default;
> +	char buffer[16];
> +	u64 msr;
> +
> +	/* Check for the SME support leaf */
> +	eax = 0x80000000;
> +	ecx = 0;
> +	native_cpuid(&eax, &ebx, &ecx, &edx);
> +	if (eax < 0x8000001f)
> +		goto out;
> +
> +	/*
> +	 * 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))
> +		goto out;

<---- newline here.

> +	me_mask = 1UL << (ebx & 0x3f);
> +
> +	/* Check if SME is enabled */
> +	msr = __rdmsr(MSR_K8_SYSCFG);
> +	if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
> +		goto out;
> +
> +	/*
> +	 * Fixups have not been applied to phys_base yet, so we must obtain
> +	 * the address to the SME command line option data in the following
> +	 * way.
> +	 */
> +	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)
> +		sme_me_mask = me_mask;

Why doesn't simply

	if (!strncmp(buffer, "on", 2))
		...

work?

-- 
Regards/Gruss,
    Boris.

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