efi.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Extensible Firmware Interface
  4 *
  5 * Based on Extensible Firmware Interface Specification version 2.4
  6 *
  7 * Copyright (C) 2013, 2014 Linaro Ltd.
  8 */
  9
 10#include <linux/efi.h>
 11#include <linux/init.h>
 12#include <linux/kmemleak.h>
 13#include <linux/kthread.h>
 14#include <linux/screen_info.h>
 15#include <linux/vmalloc.h>
 16
 17#include <asm/efi.h>
 18#include <asm/stacktrace.h>
 19#include <asm/vmap_stack.h>
 20
 21static bool region_is_misaligned(const efi_memory_desc_t *md)
 22{
 23	if (PAGE_SIZE == EFI_PAGE_SIZE)
 24		return false;
 25	return !PAGE_ALIGNED(md->phys_addr) ||
 26	       !PAGE_ALIGNED(md->num_pages << EFI_PAGE_SHIFT);
 27}
 28
 29/*
 30 * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
 31 * executable, everything else can be mapped with the XN bits
 32 * set. Also take the new (optional) RO/XP bits into account.
 33 */
 34static __init ptdesc_t create_mapping_protection(efi_memory_desc_t *md)
 35{
 36	u64 attr = md->attribute;
 37	u32 type = md->type;
 38
 39	if (type == EFI_MEMORY_MAPPED_IO) {
 40		pgprot_t prot = __pgprot(PROT_DEVICE_nGnRE);
 41
 42		if (arm64_is_protected_mmio(md->phys_addr,
 43					    md->num_pages << EFI_PAGE_SHIFT))
 44			prot = pgprot_encrypted(prot);
 45		else
 46			prot = pgprot_decrypted(prot);
 47		return pgprot_val(prot);
 48	}
 49
 50	if (region_is_misaligned(md)) {
 51		static bool __initdata code_is_misaligned;
 52
 53		/*
 54		 * Regions that are not aligned to the OS page size cannot be
 55		 * mapped with strict permissions, as those might interfere
 56		 * with the permissions that are needed by the adjacent
 57		 * region's mapping. However, if we haven't encountered any
 58		 * misaligned runtime code regions so far, we can safely use
 59		 * non-executable permissions for non-code regions.
 60		 */
 61		code_is_misaligned |= (type == EFI_RUNTIME_SERVICES_CODE);
 62
 63		return code_is_misaligned ? pgprot_val(PAGE_KERNEL_EXEC)
 64					  : pgprot_val(PAGE_KERNEL);
 65	}
 66
 67	/* R-- */
 68	if ((attr & (EFI_MEMORY_XP | EFI_MEMORY_RO)) ==
 69	    (EFI_MEMORY_XP | EFI_MEMORY_RO))
 70		return pgprot_val(PAGE_KERNEL_RO);
 71
 72	/* R-X */
 73	if (attr & EFI_MEMORY_RO)
 74		return pgprot_val(PAGE_KERNEL_ROX);
 75
 76	/* RW- */
 77	if (((attr & (EFI_MEMORY_RP | EFI_MEMORY_WP | EFI_MEMORY_XP)) ==
 78	     EFI_MEMORY_XP) ||
 79	    type != EFI_RUNTIME_SERVICES_CODE)
 80		return pgprot_val(PAGE_KERNEL);
 81
 82	/* RWX */
 83	return pgprot_val(PAGE_KERNEL_EXEC);
 84}
 85
 86int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
 87{
 88	ptdesc_t prot_val = create_mapping_protection(md);
 89	bool page_mappings_only = (md->type == EFI_RUNTIME_SERVICES_CODE ||
 90				   md->type == EFI_RUNTIME_SERVICES_DATA);
 91
 92	/*
 93	 * If this region is not aligned to the page size used by the OS, the
 94	 * mapping will be rounded outwards, and may end up sharing a page
 95	 * frame with an adjacent runtime memory region. Given that the page
 96	 * table descriptor covering the shared page will be rewritten when the
 97	 * adjacent region gets mapped, we must avoid block mappings here so we
 98	 * don't have to worry about splitting them when that happens.
 99	 */
100	if (region_is_misaligned(md))
101		page_mappings_only = true;
102
103	create_pgd_mapping(mm, md->phys_addr, md->virt_addr,
104			   md->num_pages << EFI_PAGE_SHIFT,
105			   __pgprot(prot_val | PTE_NG), page_mappings_only);
106	return 0;
107}
108
109struct set_perm_data {
110	const efi_memory_desc_t	*md;
111	bool			has_bti;
112};
113
114static int __init set_permissions(pte_t *ptep, unsigned long addr, void *data)
115{
116	struct set_perm_data *spd = data;
117	const efi_memory_desc_t *md = spd->md;
118	pte_t pte = __ptep_get(ptep);
119
120	if (md->attribute & EFI_MEMORY_RO)
121		pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
122	if (md->attribute & EFI_MEMORY_XP)
123		pte = set_pte_bit(pte, __pgprot(PTE_PXN));
124	else if (system_supports_bti_kernel() && spd->has_bti)
125		pte = set_pte_bit(pte, __pgprot(PTE_GP));
126	__set_pte(ptep, pte);
127	return 0;
128}
129
130int __init efi_set_mapping_permissions(struct mm_struct *mm,
131				       efi_memory_desc_t *md,
132				       bool has_bti)
133{
134	struct set_perm_data data = { md, has_bti };
135
136	BUG_ON(md->type != EFI_RUNTIME_SERVICES_CODE &&
137	       md->type != EFI_RUNTIME_SERVICES_DATA);
138
139	if (region_is_misaligned(md))
140		return 0;
141
142	/*
143	 * Calling apply_to_page_range() is only safe on regions that are
144	 * guaranteed to be mapped down to pages. Since we are only called
145	 * for regions that have been mapped using efi_create_mapping() above
146	 * (and this is checked by the generic Memory Attributes table parsing
147	 * routines), there is no need to check that again here.
148	 */
149	return apply_to_page_range(mm, md->virt_addr,
150				   md->num_pages << EFI_PAGE_SHIFT,
151				   set_permissions, &data);
152}
153
154/*
155 * UpdateCapsule() depends on the system being shutdown via
156 * ResetSystem().
157 */
158bool efi_poweroff_required(void)
159{
160	return efi_enabled(EFI_RUNTIME_SERVICES);
161}
162
163asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f)
164{
165	pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f);
166	return s;
167}
168
169void arch_efi_call_virt_setup(void)
170{
171	efi_runtime_assert_lock_held();
172
173	if (preemptible() && (current->flags & PF_KTHREAD)) {
174		/*
175		 * Disable migration to ensure that a preempted EFI runtime
176		 * service call will be resumed on the same CPU. This avoids
177		 * potential issues with EFI runtime calls that are preempted
178		 * while polling for an asynchronous completion of a secure
179		 * firmware call, which may not permit the CPU to change.
180		 */
181		migrate_disable();
182		kthread_use_mm(&efi_mm);
183	} else {
184		efi_virtmap_load();
185	}
186
187	/*
188	 * Enable access to the valid TTBR0_EL1 and invoke the errata
189	 * workaround directly since there is no return from exception when
190	 * invoking the EFI run-time services.
191	 */
192	uaccess_ttbr0_enable();
193	post_ttbr_update_workaround();
194
195	__efi_fpsimd_begin();
196}
197
198void arch_efi_call_virt_teardown(void)
199{
200	__efi_fpsimd_end();
201
202	/*
203	 * Defer the switch to the current thread's TTBR0_EL1 until
204	 * uaccess_enable(). Do so before efi_virtmap_unload() updates the
205	 * saved TTBR0 value, so the userland page tables are not activated
206	 * inadvertently over the back of an exception.
207	 */
208	uaccess_ttbr0_disable();
209
210	if (preemptible() && (current->flags & PF_KTHREAD)) {
211		kthread_unuse_mm(&efi_mm);
212		migrate_enable();
213	} else {
214		efi_virtmap_unload();
215	}
216}
217
218asmlinkage u64 *efi_rt_stack_top __ro_after_init;
219
220asmlinkage efi_status_t __efi_rt_asm_recover(void);
221
222bool efi_runtime_fixup_exception(struct pt_regs *regs, const char *msg)
223{
224	 /* Check whether the exception occurred while running the firmware */
225	if (!current_in_efi() || regs->pc >= TASK_SIZE_64)
226		return false;
227
228	pr_err(FW_BUG "Unable to handle %s in EFI runtime service\n", msg);
229	add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);
230	clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
231
232	regs->regs[0]	= EFI_ABORTED;
233	regs->regs[30]	= efi_rt_stack_top[-1];
234	regs->pc	= (u64)__efi_rt_asm_recover;
235
236	if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
237		regs->regs[18] = efi_rt_stack_top[-2];
238
239	return true;
240}
241
242/* EFI requires 8 KiB of stack space for runtime services */
243static_assert(THREAD_SIZE >= SZ_8K);
244
245static int __init arm64_efi_rt_init(void)
246{
247	void *p;
248
249	if (!efi_enabled(EFI_RUNTIME_SERVICES))
250		return 0;
251
252	p = arch_alloc_vmap_stack(THREAD_SIZE, NUMA_NO_NODE);
253	if (!p) {
254		pr_warn("Failed to allocate EFI runtime stack\n");
255		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
256		return -ENOMEM;
257	}
258
259	kmemleak_not_leak(p);
260	efi_rt_stack_top = p + THREAD_SIZE;
261	return 0;
262}
263core_initcall(arm64_efi_rt_init);