[RFC PATCH v4 28/28] x86: Add support to make use of Secure Memory Encryption

[Tom Lendacky]

This patch adds the 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/kernel/mem_encrypt_init.c |   71 +++++++++++++++++++++++++++++++++++-
 arch/x86/mm/mem_encrypt.c          |    2 +
 3 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index edd2f14..e6820e7 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -97,6 +97,7 @@ startup_64:
 	 * Save the returned mask in %r12 for later use.
 	 */
 	push	%rsi
+	movq	%rsi, %rdi
 	call	sme_enable
 	pop	%rsi
 	movq	%rax, %r12
diff --git a/arch/x86/kernel/mem_encrypt_init.c b/arch/x86/kernel/mem_encrypt_init.c
index 07cbb90..35c5e3d 100644
--- a/arch/x86/kernel/mem_encrypt_init.c
+++ b/arch/x86/kernel/mem_encrypt_init.c
@@ -19,6 +19,12 @@
 #include <linux/mm.h>
 
 #include <asm/sections.h>
+#include <asm/processor-flags.h>
+#include <asm/msr.h>
+#include <asm/cmdline.h>
+
+static char sme_cmdline_arg_on[] __initdata = "mem_encrypt=on";
+static char sme_cmdline_arg_off[] __initdata = "mem_encrypt=off";
 
 extern void sme_encrypt_execute(unsigned long, unsigned long, unsigned long,
 				void *, pgd_t *);
@@ -217,8 +223,71 @@ unsigned long __init sme_get_me_mask(void)
 	return sme_me_mask;
 }
 
-unsigned long __init sme_enable(void)
+unsigned long __init sme_enable(void *boot_data)
 {
+	struct boot_params *bp = boot_data;
+	unsigned int eax, ebx, ecx, edx;
+	unsigned long cmdline_ptr;
+	bool enable_if_found;
+	void *cmdline_arg;
+	u64 msr;
+
+	/* Check for an AMD processor */
+	eax = 0;
+	ecx = 0;
+	native_cpuid(&eax, &ebx, &ecx, &edx);
+	if ((ebx != 0x68747541) || (edx != 0x69746e65) || (ecx != 0x444d4163))
+		goto out;
+
+	/* 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;
+
+	/* Check if SME is enabled */
+	msr = native_read_msr(MSR_K8_SYSCFG);
+	if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
+		goto out;
+
+	/*
+	 * Fixups have not been to applied phys_base yet, so we must obtain
+	 * the address to the SME command line option in the following way.
+	 */
+	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT)) {
+		asm ("lea sme_cmdline_arg_off(%%rip), %0"
+		     : "=r" (cmdline_arg)
+		     : "p" (sme_cmdline_arg_off));
+		enable_if_found = false;
+	} else {
+		asm ("lea sme_cmdline_arg_on(%%rip), %0"
+		     : "=r" (cmdline_arg)
+		     : "p" (sme_cmdline_arg_on));
+		enable_if_found = true;
+	}
+
+	cmdline_ptr = bp->hdr.cmd_line_ptr | ((u64)bp->ext_cmd_line_ptr << 32);
+
+	if (cmdline_find_option_bool((char *)cmdline_ptr, cmdline_arg))
+		sme_me_mask = enable_if_found ? 1UL << (ebx & 0x3f) : 0;
+	else
+		sme_me_mask = enable_if_found ? 0 : 1UL << (ebx & 0x3f);
+
+out:
 	return sme_me_mask;
 }
 
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index a46bcf4..c5062e1 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -204,6 +204,8 @@ 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)