xref: /linux/arch/x86/mm/mem_encrypt_identity.c (revision 29e31a8ee811f5d85274f0381f13cd6fe650aea4)
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * AMD Memory Encryption Support
4  *
5  * Copyright (C) 2016 Advanced Micro Devices, Inc.
6  *
7  * Author: Tom Lendacky <thomas.lendacky@amd.com>
8  */
9 
10 #define DISABLE_BRANCH_PROFILING
11 
12 /*
13  * Since we're dealing with identity mappings, physical and virtual
14  * addresses are the same, so override these defines which are ultimately
15  * used by the headers in misc.h.
16  */
17 #define __pa(x)  ((unsigned long)(x))
18 #define __va(x)  ((void *)((unsigned long)(x)))
19 
20 /*
21  * Special hack: we have to be careful, because no indirections are
22  * allowed here, and paravirt_ops is a kind of one. As it will only run in
23  * baremetal anyway, we just keep it from happening. (This list needs to
24  * be extended when new paravirt and debugging variants are added.)
25  */
26 #undef CONFIG_PARAVIRT
27 #undef CONFIG_PARAVIRT_XXL
28 #undef CONFIG_PARAVIRT_SPINLOCKS
29 
30 /*
31  * This code runs before CPU feature bits are set. By default, the
32  * pgtable_l5_enabled() function uses bit X86_FEATURE_LA57 to determine if
33  * 5-level paging is active, so that won't work here. USE_EARLY_PGTABLE_L5
34  * is provided to handle this situation and, instead, use a variable that
35  * has been set by the early boot code.
36  */
37 #define USE_EARLY_PGTABLE_L5
38 
39 #include <linux/kernel.h>
40 #include <linux/mm.h>
41 #include <linux/mem_encrypt.h>
42 #include <linux/cc_platform.h>
43 
44 #include <asm/setup.h>
45 #include <asm/sections.h>
46 #include <asm/cmdline.h>
47 #include <asm/coco.h>
48 #include <asm/sev.h>
49 
50 #include "mm_internal.h"
51 
52 #define PGD_FLAGS		_KERNPG_TABLE_NOENC
53 #define P4D_FLAGS		_KERNPG_TABLE_NOENC
54 #define PUD_FLAGS		_KERNPG_TABLE_NOENC
55 #define PMD_FLAGS		_KERNPG_TABLE_NOENC
56 
57 #define PMD_FLAGS_LARGE		(__PAGE_KERNEL_LARGE_EXEC & ~_PAGE_GLOBAL)
58 
59 #define PMD_FLAGS_DEC		PMD_FLAGS_LARGE
60 #define PMD_FLAGS_DEC_WP	((PMD_FLAGS_DEC & ~_PAGE_LARGE_CACHE_MASK) | \
61 				 (_PAGE_PAT_LARGE | _PAGE_PWT))
62 
63 #define PMD_FLAGS_ENC		(PMD_FLAGS_LARGE | _PAGE_ENC)
64 
65 #define PTE_FLAGS		(__PAGE_KERNEL_EXEC & ~_PAGE_GLOBAL)
66 
67 #define PTE_FLAGS_DEC		PTE_FLAGS
68 #define PTE_FLAGS_DEC_WP	((PTE_FLAGS_DEC & ~_PAGE_CACHE_MASK) | \
69 				 (_PAGE_PAT | _PAGE_PWT))
70 
71 #define PTE_FLAGS_ENC		(PTE_FLAGS | _PAGE_ENC)
72 
73 struct sme_populate_pgd_data {
74 	void    *pgtable_area;
75 	pgd_t   *pgd;
76 
77 	pmdval_t pmd_flags;
78 	pteval_t pte_flags;
79 	unsigned long paddr;
80 
81 	unsigned long vaddr;
82 	unsigned long vaddr_end;
83 };
84 
85 /*
86  * This work area lives in the .init.scratch section, which lives outside of
87  * the kernel proper. It is sized to hold the intermediate copy buffer and
88  * more than enough pagetable pages.
89  *
90  * By using this section, the kernel can be encrypted in place and it
91  * avoids any possibility of boot parameters or initramfs images being
92  * placed such that the in-place encryption logic overwrites them.  This
93  * section is 2MB aligned to allow for simple pagetable setup using only
94  * PMD entries (see vmlinux.lds.S).
95  */
96 static char sme_workarea[2 * PMD_SIZE] __section(".init.scratch");
97 
98 static char sme_cmdline_arg[] __initdata = "mem_encrypt";
99 static char sme_cmdline_on[]  __initdata = "on";
100 static char sme_cmdline_off[] __initdata = "off";
101 
102 static void __init sme_clear_pgd(struct sme_populate_pgd_data *ppd)
103 {
104 	unsigned long pgd_start, pgd_end, pgd_size;
105 	pgd_t *pgd_p;
106 
107 	pgd_start = ppd->vaddr & PGDIR_MASK;
108 	pgd_end = ppd->vaddr_end & PGDIR_MASK;
109 
110 	pgd_size = (((pgd_end - pgd_start) / PGDIR_SIZE) + 1) * sizeof(pgd_t);
111 
112 	pgd_p = ppd->pgd + pgd_index(ppd->vaddr);
113 
114 	memset(pgd_p, 0, pgd_size);
115 }
116 
117 static pud_t __init *sme_prepare_pgd(struct sme_populate_pgd_data *ppd)
118 {
119 	pgd_t *pgd;
120 	p4d_t *p4d;
121 	pud_t *pud;
122 	pmd_t *pmd;
123 
124 	pgd = ppd->pgd + pgd_index(ppd->vaddr);
125 	if (pgd_none(*pgd)) {
126 		p4d = ppd->pgtable_area;
127 		memset(p4d, 0, sizeof(*p4d) * PTRS_PER_P4D);
128 		ppd->pgtable_area += sizeof(*p4d) * PTRS_PER_P4D;
129 		set_pgd(pgd, __pgd(PGD_FLAGS | __pa(p4d)));
130 	}
131 
132 	p4d = p4d_offset(pgd, ppd->vaddr);
133 	if (p4d_none(*p4d)) {
134 		pud = ppd->pgtable_area;
135 		memset(pud, 0, sizeof(*pud) * PTRS_PER_PUD);
136 		ppd->pgtable_area += sizeof(*pud) * PTRS_PER_PUD;
137 		set_p4d(p4d, __p4d(P4D_FLAGS | __pa(pud)));
138 	}
139 
140 	pud = pud_offset(p4d, ppd->vaddr);
141 	if (pud_none(*pud)) {
142 		pmd = ppd->pgtable_area;
143 		memset(pmd, 0, sizeof(*pmd) * PTRS_PER_PMD);
144 		ppd->pgtable_area += sizeof(*pmd) * PTRS_PER_PMD;
145 		set_pud(pud, __pud(PUD_FLAGS | __pa(pmd)));
146 	}
147 
148 	if (pud_large(*pud))
149 		return NULL;
150 
151 	return pud;
152 }
153 
154 static void __init sme_populate_pgd_large(struct sme_populate_pgd_data *ppd)
155 {
156 	pud_t *pud;
157 	pmd_t *pmd;
158 
159 	pud = sme_prepare_pgd(ppd);
160 	if (!pud)
161 		return;
162 
163 	pmd = pmd_offset(pud, ppd->vaddr);
164 	if (pmd_large(*pmd))
165 		return;
166 
167 	set_pmd(pmd, __pmd(ppd->paddr | ppd->pmd_flags));
168 }
169 
170 static void __init sme_populate_pgd(struct sme_populate_pgd_data *ppd)
171 {
172 	pud_t *pud;
173 	pmd_t *pmd;
174 	pte_t *pte;
175 
176 	pud = sme_prepare_pgd(ppd);
177 	if (!pud)
178 		return;
179 
180 	pmd = pmd_offset(pud, ppd->vaddr);
181 	if (pmd_none(*pmd)) {
182 		pte = ppd->pgtable_area;
183 		memset(pte, 0, sizeof(*pte) * PTRS_PER_PTE);
184 		ppd->pgtable_area += sizeof(*pte) * PTRS_PER_PTE;
185 		set_pmd(pmd, __pmd(PMD_FLAGS | __pa(pte)));
186 	}
187 
188 	if (pmd_large(*pmd))
189 		return;
190 
191 	pte = pte_offset_map(pmd, ppd->vaddr);
192 	if (pte_none(*pte))
193 		set_pte(pte, __pte(ppd->paddr | ppd->pte_flags));
194 }
195 
196 static void __init __sme_map_range_pmd(struct sme_populate_pgd_data *ppd)
197 {
198 	while (ppd->vaddr < ppd->vaddr_end) {
199 		sme_populate_pgd_large(ppd);
200 
201 		ppd->vaddr += PMD_SIZE;
202 		ppd->paddr += PMD_SIZE;
203 	}
204 }
205 
206 static void __init __sme_map_range_pte(struct sme_populate_pgd_data *ppd)
207 {
208 	while (ppd->vaddr < ppd->vaddr_end) {
209 		sme_populate_pgd(ppd);
210 
211 		ppd->vaddr += PAGE_SIZE;
212 		ppd->paddr += PAGE_SIZE;
213 	}
214 }
215 
216 static void __init __sme_map_range(struct sme_populate_pgd_data *ppd,
217 				   pmdval_t pmd_flags, pteval_t pte_flags)
218 {
219 	unsigned long vaddr_end;
220 
221 	ppd->pmd_flags = pmd_flags;
222 	ppd->pte_flags = pte_flags;
223 
224 	/* Save original end value since we modify the struct value */
225 	vaddr_end = ppd->vaddr_end;
226 
227 	/* If start is not 2MB aligned, create PTE entries */
228 	ppd->vaddr_end = ALIGN(ppd->vaddr, PMD_SIZE);
229 	__sme_map_range_pte(ppd);
230 
231 	/* Create PMD entries */
232 	ppd->vaddr_end = vaddr_end & PMD_MASK;
233 	__sme_map_range_pmd(ppd);
234 
235 	/* If end is not 2MB aligned, create PTE entries */
236 	ppd->vaddr_end = vaddr_end;
237 	__sme_map_range_pte(ppd);
238 }
239 
240 static void __init sme_map_range_encrypted(struct sme_populate_pgd_data *ppd)
241 {
242 	__sme_map_range(ppd, PMD_FLAGS_ENC, PTE_FLAGS_ENC);
243 }
244 
245 static void __init sme_map_range_decrypted(struct sme_populate_pgd_data *ppd)
246 {
247 	__sme_map_range(ppd, PMD_FLAGS_DEC, PTE_FLAGS_DEC);
248 }
249 
250 static void __init sme_map_range_decrypted_wp(struct sme_populate_pgd_data *ppd)
251 {
252 	__sme_map_range(ppd, PMD_FLAGS_DEC_WP, PTE_FLAGS_DEC_WP);
253 }
254 
255 static unsigned long __init sme_pgtable_calc(unsigned long len)
256 {
257 	unsigned long entries = 0, tables = 0;
258 
259 	/*
260 	 * Perform a relatively simplistic calculation of the pagetable
261 	 * entries that are needed. Those mappings will be covered mostly
262 	 * by 2MB PMD entries so we can conservatively calculate the required
263 	 * number of P4D, PUD and PMD structures needed to perform the
264 	 * mappings.  For mappings that are not 2MB aligned, PTE mappings
265 	 * would be needed for the start and end portion of the address range
266 	 * that fall outside of the 2MB alignment.  This results in, at most,
267 	 * two extra pages to hold PTE entries for each range that is mapped.
268 	 * Incrementing the count for each covers the case where the addresses
269 	 * cross entries.
270 	 */
271 
272 	/* PGDIR_SIZE is equal to P4D_SIZE on 4-level machine. */
273 	if (PTRS_PER_P4D > 1)
274 		entries += (DIV_ROUND_UP(len, PGDIR_SIZE) + 1) * sizeof(p4d_t) * PTRS_PER_P4D;
275 	entries += (DIV_ROUND_UP(len, P4D_SIZE) + 1) * sizeof(pud_t) * PTRS_PER_PUD;
276 	entries += (DIV_ROUND_UP(len, PUD_SIZE) + 1) * sizeof(pmd_t) * PTRS_PER_PMD;
277 	entries += 2 * sizeof(pte_t) * PTRS_PER_PTE;
278 
279 	/*
280 	 * Now calculate the added pagetable structures needed to populate
281 	 * the new pagetables.
282 	 */
283 
284 	if (PTRS_PER_P4D > 1)
285 		tables += DIV_ROUND_UP(entries, PGDIR_SIZE) * sizeof(p4d_t) * PTRS_PER_P4D;
286 	tables += DIV_ROUND_UP(entries, P4D_SIZE) * sizeof(pud_t) * PTRS_PER_PUD;
287 	tables += DIV_ROUND_UP(entries, PUD_SIZE) * sizeof(pmd_t) * PTRS_PER_PMD;
288 
289 	return entries + tables;
290 }
291 
292 void __init sme_encrypt_kernel(struct boot_params *bp)
293 {
294 	unsigned long workarea_start, workarea_end, workarea_len;
295 	unsigned long execute_start, execute_end, execute_len;
296 	unsigned long kernel_start, kernel_end, kernel_len;
297 	unsigned long initrd_start, initrd_end, initrd_len;
298 	struct sme_populate_pgd_data ppd;
299 	unsigned long pgtable_area_len;
300 	unsigned long decrypted_base;
301 
302 	/*
303 	 * This is early code, use an open coded check for SME instead of
304 	 * using cc_platform_has(). This eliminates worries about removing
305 	 * instrumentation or checking boot_cpu_data in the cc_platform_has()
306 	 * function.
307 	 */
308 	if (!sme_get_me_mask() || sev_status & MSR_AMD64_SEV_ENABLED)
309 		return;
310 
311 	/*
312 	 * Prepare for encrypting the kernel and initrd by building new
313 	 * pagetables with the necessary attributes needed to encrypt the
314 	 * kernel in place.
315 	 *
316 	 *   One range of virtual addresses will map the memory occupied
317 	 *   by the kernel and initrd as encrypted.
318 	 *
319 	 *   Another range of virtual addresses will map the memory occupied
320 	 *   by the kernel and initrd as decrypted and write-protected.
321 	 *
322 	 *     The use of write-protect attribute will prevent any of the
323 	 *     memory from being cached.
324 	 */
325 
326 	/* Physical addresses gives us the identity mapped virtual addresses */
327 	kernel_start = __pa_symbol(_text);
328 	kernel_end = ALIGN(__pa_symbol(_end), PMD_SIZE);
329 	kernel_len = kernel_end - kernel_start;
330 
331 	initrd_start = 0;
332 	initrd_end = 0;
333 	initrd_len = 0;
334 #ifdef CONFIG_BLK_DEV_INITRD
335 	initrd_len = (unsigned long)bp->hdr.ramdisk_size |
336 		     ((unsigned long)bp->ext_ramdisk_size << 32);
337 	if (initrd_len) {
338 		initrd_start = (unsigned long)bp->hdr.ramdisk_image |
339 			       ((unsigned long)bp->ext_ramdisk_image << 32);
340 		initrd_end = PAGE_ALIGN(initrd_start + initrd_len);
341 		initrd_len = initrd_end - initrd_start;
342 	}
343 #endif
344 
345 	/*
346 	 * We're running identity mapped, so we must obtain the address to the
347 	 * SME encryption workarea using rip-relative addressing.
348 	 */
349 	asm ("lea sme_workarea(%%rip), %0"
350 	     : "=r" (workarea_start)
351 	     : "p" (sme_workarea));
352 
353 	/*
354 	 * Calculate required number of workarea bytes needed:
355 	 *   executable encryption area size:
356 	 *     stack page (PAGE_SIZE)
357 	 *     encryption routine page (PAGE_SIZE)
358 	 *     intermediate copy buffer (PMD_SIZE)
359 	 *   pagetable structures for the encryption of the kernel
360 	 *   pagetable structures for workarea (in case not currently mapped)
361 	 */
362 	execute_start = workarea_start;
363 	execute_end = execute_start + (PAGE_SIZE * 2) + PMD_SIZE;
364 	execute_len = execute_end - execute_start;
365 
366 	/*
367 	 * One PGD for both encrypted and decrypted mappings and a set of
368 	 * PUDs and PMDs for each of the encrypted and decrypted mappings.
369 	 */
370 	pgtable_area_len = sizeof(pgd_t) * PTRS_PER_PGD;
371 	pgtable_area_len += sme_pgtable_calc(execute_end - kernel_start) * 2;
372 	if (initrd_len)
373 		pgtable_area_len += sme_pgtable_calc(initrd_len) * 2;
374 
375 	/* PUDs and PMDs needed in the current pagetables for the workarea */
376 	pgtable_area_len += sme_pgtable_calc(execute_len + pgtable_area_len);
377 
378 	/*
379 	 * The total workarea includes the executable encryption area and
380 	 * the pagetable area. The start of the workarea is already 2MB
381 	 * aligned, align the end of the workarea on a 2MB boundary so that
382 	 * we don't try to create/allocate PTE entries from the workarea
383 	 * before it is mapped.
384 	 */
385 	workarea_len = execute_len + pgtable_area_len;
386 	workarea_end = ALIGN(workarea_start + workarea_len, PMD_SIZE);
387 
388 	/*
389 	 * Set the address to the start of where newly created pagetable
390 	 * structures (PGDs, PUDs and PMDs) will be allocated. New pagetable
391 	 * structures are created when the workarea is added to the current
392 	 * pagetables and when the new encrypted and decrypted kernel
393 	 * mappings are populated.
394 	 */
395 	ppd.pgtable_area = (void *)execute_end;
396 
397 	/*
398 	 * Make sure the current pagetable structure has entries for
399 	 * addressing the workarea.
400 	 */
401 	ppd.pgd = (pgd_t *)native_read_cr3_pa();
402 	ppd.paddr = workarea_start;
403 	ppd.vaddr = workarea_start;
404 	ppd.vaddr_end = workarea_end;
405 	sme_map_range_decrypted(&ppd);
406 
407 	/* Flush the TLB - no globals so cr3 is enough */
408 	native_write_cr3(__native_read_cr3());
409 
410 	/*
411 	 * A new pagetable structure is being built to allow for the kernel
412 	 * and initrd to be encrypted. It starts with an empty PGD that will
413 	 * then be populated with new PUDs and PMDs as the encrypted and
414 	 * decrypted kernel mappings are created.
415 	 */
416 	ppd.pgd = ppd.pgtable_area;
417 	memset(ppd.pgd, 0, sizeof(pgd_t) * PTRS_PER_PGD);
418 	ppd.pgtable_area += sizeof(pgd_t) * PTRS_PER_PGD;
419 
420 	/*
421 	 * A different PGD index/entry must be used to get different
422 	 * pagetable entries for the decrypted mapping. Choose the next
423 	 * PGD index and convert it to a virtual address to be used as
424 	 * the base of the mapping.
425 	 */
426 	decrypted_base = (pgd_index(workarea_end) + 1) & (PTRS_PER_PGD - 1);
427 	if (initrd_len) {
428 		unsigned long check_base;
429 
430 		check_base = (pgd_index(initrd_end) + 1) & (PTRS_PER_PGD - 1);
431 		decrypted_base = max(decrypted_base, check_base);
432 	}
433 	decrypted_base <<= PGDIR_SHIFT;
434 
435 	/* Add encrypted kernel (identity) mappings */
436 	ppd.paddr = kernel_start;
437 	ppd.vaddr = kernel_start;
438 	ppd.vaddr_end = kernel_end;
439 	sme_map_range_encrypted(&ppd);
440 
441 	/* Add decrypted, write-protected kernel (non-identity) mappings */
442 	ppd.paddr = kernel_start;
443 	ppd.vaddr = kernel_start + decrypted_base;
444 	ppd.vaddr_end = kernel_end + decrypted_base;
445 	sme_map_range_decrypted_wp(&ppd);
446 
447 	if (initrd_len) {
448 		/* Add encrypted initrd (identity) mappings */
449 		ppd.paddr = initrd_start;
450 		ppd.vaddr = initrd_start;
451 		ppd.vaddr_end = initrd_end;
452 		sme_map_range_encrypted(&ppd);
453 		/*
454 		 * Add decrypted, write-protected initrd (non-identity) mappings
455 		 */
456 		ppd.paddr = initrd_start;
457 		ppd.vaddr = initrd_start + decrypted_base;
458 		ppd.vaddr_end = initrd_end + decrypted_base;
459 		sme_map_range_decrypted_wp(&ppd);
460 	}
461 
462 	/* Add decrypted workarea mappings to both kernel mappings */
463 	ppd.paddr = workarea_start;
464 	ppd.vaddr = workarea_start;
465 	ppd.vaddr_end = workarea_end;
466 	sme_map_range_decrypted(&ppd);
467 
468 	ppd.paddr = workarea_start;
469 	ppd.vaddr = workarea_start + decrypted_base;
470 	ppd.vaddr_end = workarea_end + decrypted_base;
471 	sme_map_range_decrypted(&ppd);
472 
473 	/* Perform the encryption */
474 	sme_encrypt_execute(kernel_start, kernel_start + decrypted_base,
475 			    kernel_len, workarea_start, (unsigned long)ppd.pgd);
476 
477 	if (initrd_len)
478 		sme_encrypt_execute(initrd_start, initrd_start + decrypted_base,
479 				    initrd_len, workarea_start,
480 				    (unsigned long)ppd.pgd);
481 
482 	/*
483 	 * At this point we are running encrypted.  Remove the mappings for
484 	 * the decrypted areas - all that is needed for this is to remove
485 	 * the PGD entry/entries.
486 	 */
487 	ppd.vaddr = kernel_start + decrypted_base;
488 	ppd.vaddr_end = kernel_end + decrypted_base;
489 	sme_clear_pgd(&ppd);
490 
491 	if (initrd_len) {
492 		ppd.vaddr = initrd_start + decrypted_base;
493 		ppd.vaddr_end = initrd_end + decrypted_base;
494 		sme_clear_pgd(&ppd);
495 	}
496 
497 	ppd.vaddr = workarea_start + decrypted_base;
498 	ppd.vaddr_end = workarea_end + decrypted_base;
499 	sme_clear_pgd(&ppd);
500 
501 	/* Flush the TLB - no globals so cr3 is enough */
502 	native_write_cr3(__native_read_cr3());
503 }
504 
505 void __init sme_enable(struct boot_params *bp)
506 {
507 	const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
508 	unsigned int eax, ebx, ecx, edx;
509 	unsigned long feature_mask;
510 	bool active_by_default;
511 	unsigned long me_mask;
512 	char buffer[16];
513 	bool snp;
514 	u64 msr;
515 
516 	snp = snp_init(bp);
517 
518 	/* Check for the SME/SEV support leaf */
519 	eax = 0x80000000;
520 	ecx = 0;
521 	native_cpuid(&eax, &ebx, &ecx, &edx);
522 	if (eax < 0x8000001f)
523 		return;
524 
525 #define AMD_SME_BIT	BIT(0)
526 #define AMD_SEV_BIT	BIT(1)
527 
528 	/*
529 	 * Check for the SME/SEV feature:
530 	 *   CPUID Fn8000_001F[EAX]
531 	 *   - Bit 0 - Secure Memory Encryption support
532 	 *   - Bit 1 - Secure Encrypted Virtualization support
533 	 *   CPUID Fn8000_001F[EBX]
534 	 *   - Bits 5:0 - Pagetable bit position used to indicate encryption
535 	 */
536 	eax = 0x8000001f;
537 	ecx = 0;
538 	native_cpuid(&eax, &ebx, &ecx, &edx);
539 	/* Check whether SEV or SME is supported */
540 	if (!(eax & (AMD_SEV_BIT | AMD_SME_BIT)))
541 		return;
542 
543 	me_mask = 1UL << (ebx & 0x3f);
544 
545 	/* Check the SEV MSR whether SEV or SME is enabled */
546 	sev_status   = __rdmsr(MSR_AMD64_SEV);
547 	feature_mask = (sev_status & MSR_AMD64_SEV_ENABLED) ? AMD_SEV_BIT : AMD_SME_BIT;
548 
549 	/* The SEV-SNP CC blob should never be present unless SEV-SNP is enabled. */
550 	if (snp && !(sev_status & MSR_AMD64_SEV_SNP_ENABLED))
551 		snp_abort();
552 
553 	/* Check if memory encryption is enabled */
554 	if (feature_mask == AMD_SME_BIT) {
555 		/*
556 		 * No SME if Hypervisor bit is set. This check is here to
557 		 * prevent a guest from trying to enable SME. For running as a
558 		 * KVM guest the MSR_AMD64_SYSCFG will be sufficient, but there
559 		 * might be other hypervisors which emulate that MSR as non-zero
560 		 * or even pass it through to the guest.
561 		 * A malicious hypervisor can still trick a guest into this
562 		 * path, but there is no way to protect against that.
563 		 */
564 		eax = 1;
565 		ecx = 0;
566 		native_cpuid(&eax, &ebx, &ecx, &edx);
567 		if (ecx & BIT(31))
568 			return;
569 
570 		/* For SME, check the SYSCFG MSR */
571 		msr = __rdmsr(MSR_AMD64_SYSCFG);
572 		if (!(msr & MSR_AMD64_SYSCFG_MEM_ENCRYPT))
573 			return;
574 	} else {
575 		/* SEV state cannot be controlled by a command line option */
576 		sme_me_mask = me_mask;
577 		goto out;
578 	}
579 
580 	/*
581 	 * Fixups have not been applied to phys_base yet and we're running
582 	 * identity mapped, so we must obtain the address to the SME command
583 	 * line argument data using rip-relative addressing.
584 	 */
585 	asm ("lea sme_cmdline_arg(%%rip), %0"
586 	     : "=r" (cmdline_arg)
587 	     : "p" (sme_cmdline_arg));
588 	asm ("lea sme_cmdline_on(%%rip), %0"
589 	     : "=r" (cmdline_on)
590 	     : "p" (sme_cmdline_on));
591 	asm ("lea sme_cmdline_off(%%rip), %0"
592 	     : "=r" (cmdline_off)
593 	     : "p" (sme_cmdline_off));
594 
595 	if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
596 		active_by_default = true;
597 	else
598 		active_by_default = false;
599 
600 	cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr |
601 				     ((u64)bp->ext_cmd_line_ptr << 32));
602 
603 	if (cmdline_find_option(cmdline_ptr, cmdline_arg, buffer, sizeof(buffer)) < 0)
604 		return;
605 
606 	if (!strncmp(buffer, cmdline_on, sizeof(buffer)))
607 		sme_me_mask = me_mask;
608 	else if (!strncmp(buffer, cmdline_off, sizeof(buffer)))
609 		sme_me_mask = 0;
610 	else
611 		sme_me_mask = active_by_default ? me_mask : 0;
612 out:
613 	if (sme_me_mask) {
614 		physical_mask &= ~sme_me_mask;
615 		cc_set_vendor(CC_VENDOR_AMD);
616 		cc_set_mask(sme_me_mask);
617 	}
618 }
619