xref: /openbmc/linux/arch/arm64/kernel/efi.c (revision 6db6b729)
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/screen_info.h>
13 
14 #include <asm/efi.h>
15 #include <asm/stacktrace.h>
16 
17 static bool region_is_misaligned(const efi_memory_desc_t *md)
18 {
19 	if (PAGE_SIZE == EFI_PAGE_SIZE)
20 		return false;
21 	return !PAGE_ALIGNED(md->phys_addr) ||
22 	       !PAGE_ALIGNED(md->num_pages << EFI_PAGE_SHIFT);
23 }
24 
25 /*
26  * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
27  * executable, everything else can be mapped with the XN bits
28  * set. Also take the new (optional) RO/XP bits into account.
29  */
30 static __init pteval_t create_mapping_protection(efi_memory_desc_t *md)
31 {
32 	u64 attr = md->attribute;
33 	u32 type = md->type;
34 
35 	if (type == EFI_MEMORY_MAPPED_IO)
36 		return PROT_DEVICE_nGnRE;
37 
38 	if (region_is_misaligned(md)) {
39 		static bool __initdata code_is_misaligned;
40 
41 		/*
42 		 * Regions that are not aligned to the OS page size cannot be
43 		 * mapped with strict permissions, as those might interfere
44 		 * with the permissions that are needed by the adjacent
45 		 * region's mapping. However, if we haven't encountered any
46 		 * misaligned runtime code regions so far, we can safely use
47 		 * non-executable permissions for non-code regions.
48 		 */
49 		code_is_misaligned |= (type == EFI_RUNTIME_SERVICES_CODE);
50 
51 		return code_is_misaligned ? pgprot_val(PAGE_KERNEL_EXEC)
52 					  : pgprot_val(PAGE_KERNEL);
53 	}
54 
55 	/* R-- */
56 	if ((attr & (EFI_MEMORY_XP | EFI_MEMORY_RO)) ==
57 	    (EFI_MEMORY_XP | EFI_MEMORY_RO))
58 		return pgprot_val(PAGE_KERNEL_RO);
59 
60 	/* R-X */
61 	if (attr & EFI_MEMORY_RO)
62 		return pgprot_val(PAGE_KERNEL_ROX);
63 
64 	/* RW- */
65 	if (((attr & (EFI_MEMORY_RP | EFI_MEMORY_WP | EFI_MEMORY_XP)) ==
66 	     EFI_MEMORY_XP) ||
67 	    type != EFI_RUNTIME_SERVICES_CODE)
68 		return pgprot_val(PAGE_KERNEL);
69 
70 	/* RWX */
71 	return pgprot_val(PAGE_KERNEL_EXEC);
72 }
73 
74 /* we will fill this structure from the stub, so don't put it in .bss */
75 struct screen_info screen_info __section(".data");
76 EXPORT_SYMBOL(screen_info);
77 
78 int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
79 {
80 	pteval_t prot_val = create_mapping_protection(md);
81 	bool page_mappings_only = (md->type == EFI_RUNTIME_SERVICES_CODE ||
82 				   md->type == EFI_RUNTIME_SERVICES_DATA);
83 
84 	/*
85 	 * If this region is not aligned to the page size used by the OS, the
86 	 * mapping will be rounded outwards, and may end up sharing a page
87 	 * frame with an adjacent runtime memory region. Given that the page
88 	 * table descriptor covering the shared page will be rewritten when the
89 	 * adjacent region gets mapped, we must avoid block mappings here so we
90 	 * don't have to worry about splitting them when that happens.
91 	 */
92 	if (region_is_misaligned(md))
93 		page_mappings_only = true;
94 
95 	create_pgd_mapping(mm, md->phys_addr, md->virt_addr,
96 			   md->num_pages << EFI_PAGE_SHIFT,
97 			   __pgprot(prot_val | PTE_NG), page_mappings_only);
98 	return 0;
99 }
100 
101 struct set_perm_data {
102 	const efi_memory_desc_t	*md;
103 	bool			has_bti;
104 };
105 
106 static int __init set_permissions(pte_t *ptep, unsigned long addr, void *data)
107 {
108 	struct set_perm_data *spd = data;
109 	const efi_memory_desc_t *md = spd->md;
110 	pte_t pte = READ_ONCE(*ptep);
111 
112 	if (md->attribute & EFI_MEMORY_RO)
113 		pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
114 	if (md->attribute & EFI_MEMORY_XP)
115 		pte = set_pte_bit(pte, __pgprot(PTE_PXN));
116 	else if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) &&
117 		 system_supports_bti() && spd->has_bti)
118 		pte = set_pte_bit(pte, __pgprot(PTE_GP));
119 	set_pte(ptep, pte);
120 	return 0;
121 }
122 
123 int __init efi_set_mapping_permissions(struct mm_struct *mm,
124 				       efi_memory_desc_t *md,
125 				       bool has_bti)
126 {
127 	struct set_perm_data data = { md, has_bti };
128 
129 	BUG_ON(md->type != EFI_RUNTIME_SERVICES_CODE &&
130 	       md->type != EFI_RUNTIME_SERVICES_DATA);
131 
132 	if (region_is_misaligned(md))
133 		return 0;
134 
135 	/*
136 	 * Calling apply_to_page_range() is only safe on regions that are
137 	 * guaranteed to be mapped down to pages. Since we are only called
138 	 * for regions that have been mapped using efi_create_mapping() above
139 	 * (and this is checked by the generic Memory Attributes table parsing
140 	 * routines), there is no need to check that again here.
141 	 */
142 	return apply_to_page_range(mm, md->virt_addr,
143 				   md->num_pages << EFI_PAGE_SHIFT,
144 				   set_permissions, &data);
145 }
146 
147 /*
148  * UpdateCapsule() depends on the system being shutdown via
149  * ResetSystem().
150  */
151 bool efi_poweroff_required(void)
152 {
153 	return efi_enabled(EFI_RUNTIME_SERVICES);
154 }
155 
156 asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f)
157 {
158 	pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f);
159 	return s;
160 }
161 
162 static DEFINE_RAW_SPINLOCK(efi_rt_lock);
163 
164 void arch_efi_call_virt_setup(void)
165 {
166 	efi_virtmap_load();
167 	__efi_fpsimd_begin();
168 	raw_spin_lock(&efi_rt_lock);
169 }
170 
171 void arch_efi_call_virt_teardown(void)
172 {
173 	raw_spin_unlock(&efi_rt_lock);
174 	__efi_fpsimd_end();
175 	efi_virtmap_unload();
176 }
177 
178 asmlinkage u64 *efi_rt_stack_top __ro_after_init;
179 
180 asmlinkage efi_status_t __efi_rt_asm_recover(void);
181 
182 bool efi_runtime_fixup_exception(struct pt_regs *regs, const char *msg)
183 {
184 	 /* Check whether the exception occurred while running the firmware */
185 	if (!current_in_efi() || regs->pc >= TASK_SIZE_64)
186 		return false;
187 
188 	pr_err(FW_BUG "Unable to handle %s in EFI runtime service\n", msg);
189 	add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);
190 	clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
191 
192 	regs->regs[0]	= EFI_ABORTED;
193 	regs->regs[30]	= efi_rt_stack_top[-1];
194 	regs->pc	= (u64)__efi_rt_asm_recover;
195 
196 	if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
197 		regs->regs[18] = efi_rt_stack_top[-2];
198 
199 	return true;
200 }
201 
202 /* EFI requires 8 KiB of stack space for runtime services */
203 static_assert(THREAD_SIZE >= SZ_8K);
204 
205 static int __init arm64_efi_rt_init(void)
206 {
207 	void *p;
208 
209 	if (!efi_enabled(EFI_RUNTIME_SERVICES))
210 		return 0;
211 
212 	p = __vmalloc_node(THREAD_SIZE, THREAD_ALIGN, GFP_KERNEL,
213 			   NUMA_NO_NODE, &&l);
214 l:	if (!p) {
215 		pr_warn("Failed to allocate EFI runtime stack\n");
216 		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
217 		return -ENOMEM;
218 	}
219 
220 	efi_rt_stack_top = p + THREAD_SIZE;
221 	return 0;
222 }
223 core_initcall(arm64_efi_rt_init);
224