1 files changed, 753 insertions, 0 deletions

diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
new file mode 100644
index 000000000..c1eec019d
--- /dev/null
+++ b/arch/x86/platform/efi/quirks.c
@@ -0,0 +1,753 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#define pr_fmt(fmt) "efi: " fmt
+
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/time.h>
+#include <linux/types.h>
+#include <linux/efi.h>
+#include <linux/slab.h>
+#include <linux/memblock.h>
+#include <linux/acpi.h>
+#include <linux/dmi.h>
+
+#include <asm/e820/api.h>
+#include <asm/efi.h>
+#include <asm/uv/uv.h>
+#include <asm/cpu_device_id.h>
+#include <asm/realmode.h>
+#include <asm/reboot.h>
+
+#define EFI_MIN_RESERVE 5120
+
+#define EFI_DUMMY_GUID \
+	EFI_GUID(0x4424ac57, 0xbe4b, 0x47dd, 0x9e, 0x97, 0xed, 0x50, 0xf0, 0x9f, 0x92, 0xa9)
+
+#define QUARK_CSH_SIGNATURE		0x5f435348	/* _CSH */
+#define QUARK_SECURITY_HEADER_SIZE	0x400
+
+/*
+ * Header prepended to the standard EFI capsule on Quark systems the are based
+ * on Intel firmware BSP.
+ * @csh_signature:	Unique identifier to sanity check signed module
+ * 			presence ("_CSH").
+ * @version:		Current version of CSH used. Should be one for Quark A0.
+ * @modulesize:		Size of the entire module including the module header
+ * 			and payload.
+ * @security_version_number_index: Index of SVN to use for validation of signed
+ * 			module.
+ * @security_version_number: Used to prevent against roll back of modules.
+ * @rsvd_module_id:	Currently unused for Clanton (Quark).
+ * @rsvd_module_vendor:	Vendor Identifier. For Intel products value is
+ * 			0x00008086.
+ * @rsvd_date:		BCD representation of build date as yyyymmdd, where
+ * 			yyyy=4 digit year, mm=1-12, dd=1-31.
+ * @headersize:		Total length of the header including including any
+ * 			padding optionally added by the signing tool.
+ * @hash_algo:		What Hash is used in the module signing.
+ * @cryp_algo:		What Crypto is used in the module signing.
+ * @keysize:		Total length of the key data including including any
+ * 			padding optionally added by the signing tool.
+ * @signaturesize:	Total length of the signature including including any
+ * 			padding optionally added by the signing tool.
+ * @rsvd_next_header:	32-bit pointer to the next Secure Boot Module in the
+ * 			chain, if there is a next header.
+ * @rsvd:		Reserved, padding structure to required size.
+ *
+ * See also QuartSecurityHeader_t in
+ * Quark_EDKII_v1.2.1.1/QuarkPlatformPkg/Include/QuarkBootRom.h
+ * from https://downloadcenter.intel.com/download/23197/Intel-Quark-SoC-X1000-Board-Support-Package-BSP
+ */
+struct quark_security_header {
+	u32 csh_signature;
+	u32 version;
+	u32 modulesize;
+	u32 security_version_number_index;
+	u32 security_version_number;
+	u32 rsvd_module_id;
+	u32 rsvd_module_vendor;
+	u32 rsvd_date;
+	u32 headersize;
+	u32 hash_algo;
+	u32 cryp_algo;
+	u32 keysize;
+	u32 signaturesize;
+	u32 rsvd_next_header;
+	u32 rsvd[2];
+};
+
+static const efi_char16_t efi_dummy_name[] = L"DUMMY";
+
+static bool efi_no_storage_paranoia;
+
+/*
+ * Some firmware implementations refuse to boot if there's insufficient
+ * space in the variable store. The implementation of garbage collection
+ * in some FW versions causes stale (deleted) variables to take up space
+ * longer than intended and space is only freed once the store becomes
+ * almost completely full.
+ *
+ * Enabling this option disables the space checks in
+ * efi_query_variable_store() and forces garbage collection.
+ *
+ * Only enable this option if deleting EFI variables does not free up
+ * space in your variable store, e.g. if despite deleting variables
+ * you're unable to create new ones.
+ */
+static int __init setup_storage_paranoia(char *arg)
+{
+	efi_no_storage_paranoia = true;
+	return 0;
+}
+early_param("efi_no_storage_paranoia", setup_storage_paranoia);
+
+/*
+ * Deleting the dummy variable which kicks off garbage collection
+*/
+void efi_delete_dummy_variable(void)
+{
+	efi.set_variable_nonblocking((efi_char16_t *)efi_dummy_name,
+				     &EFI_DUMMY_GUID,
+				     EFI_VARIABLE_NON_VOLATILE |
+				     EFI_VARIABLE_BOOTSERVICE_ACCESS |
+				     EFI_VARIABLE_RUNTIME_ACCESS, 0, NULL);
+}
+
+/*
+ * In the nonblocking case we do not attempt to perform garbage
+ * collection if we do not have enough free space. Rather, we do the
+ * bare minimum check and give up immediately if the available space
+ * is below EFI_MIN_RESERVE.
+ *
+ * This function is intended to be small and simple because it is
+ * invoked from crash handler paths.
+ */
+static efi_status_t
+query_variable_store_nonblocking(u32 attributes, unsigned long size)
+{
+	efi_status_t status;
+	u64 storage_size, remaining_size, max_size;
+
+	status = efi.query_variable_info_nonblocking(attributes, &storage_size,
+						     &remaining_size,
+						     &max_size);
+	if (status != EFI_SUCCESS)
+		return status;
+
+	if (remaining_size - size < EFI_MIN_RESERVE)
+		return EFI_OUT_OF_RESOURCES;
+
+	return EFI_SUCCESS;
+}
+
+/*
+ * Some firmware implementations refuse to boot if there's insufficient space
+ * in the variable store. Ensure that we never use more than a safe limit.
+ *
+ * Return EFI_SUCCESS if it is safe to write 'size' bytes to the variable
+ * store.
+ */
+efi_status_t efi_query_variable_store(u32 attributes, unsigned long size,
+				      bool nonblocking)
+{
+	efi_status_t status;
+	u64 storage_size, remaining_size, max_size;
+
+	if (!(attributes & EFI_VARIABLE_NON_VOLATILE))
+		return 0;
+
+	if (nonblocking)
+		return query_variable_store_nonblocking(attributes, size);
+
+	status = efi.query_variable_info(attributes, &storage_size,
+					 &remaining_size, &max_size);
+	if (status != EFI_SUCCESS)
+		return status;
+
+	/*
+	 * We account for that by refusing the write if permitting it would
+	 * reduce the available space to under 5KB. This figure was provided by
+	 * Samsung, so should be safe.
+	 */
+	if ((remaining_size - size < EFI_MIN_RESERVE) &&
+		!efi_no_storage_paranoia) {
+
+		/*
+		 * Triggering garbage collection may require that the firmware
+		 * generate a real EFI_OUT_OF_RESOURCES error. We can force
+		 * that by attempting to use more space than is available.
+		 */
+		unsigned long dummy_size = remaining_size + 1024;
+		void *dummy = kzalloc(dummy_size, GFP_KERNEL);
+
+		if (!dummy)
+			return EFI_OUT_OF_RESOURCES;
+
+		status = efi.set_variable((efi_char16_t *)efi_dummy_name,
+					  &EFI_DUMMY_GUID,
+					  EFI_VARIABLE_NON_VOLATILE |
+					  EFI_VARIABLE_BOOTSERVICE_ACCESS |
+					  EFI_VARIABLE_RUNTIME_ACCESS,
+					  dummy_size, dummy);
+
+		if (status == EFI_SUCCESS) {
+			/*
+			 * This should have failed, so if it didn't make sure
+			 * that we delete it...
+			 */
+			efi_delete_dummy_variable();
+		}
+
+		kfree(dummy);
+
+		/*
+		 * The runtime code may now have triggered a garbage collection
+		 * run, so check the variable info again
+		 */
+		status = efi.query_variable_info(attributes, &storage_size,
+						 &remaining_size, &max_size);
+
+		if (status != EFI_SUCCESS)
+			return status;
+
+		/*
+		 * There still isn't enough room, so return an error
+		 */
+		if (remaining_size - size < EFI_MIN_RESERVE)
+			return EFI_OUT_OF_RESOURCES;
+	}
+
+	return EFI_SUCCESS;
+}
+EXPORT_SYMBOL_GPL(efi_query_variable_store);
+
+/*
+ * The UEFI specification makes it clear that the operating system is
+ * free to do whatever it wants with boot services code after
+ * ExitBootServices() has been called. Ignoring this recommendation a
+ * significant bunch of EFI implementations continue calling into boot
+ * services code (SetVirtualAddressMap). In order to work around such
+ * buggy implementations we reserve boot services region during EFI
+ * init and make sure it stays executable. Then, after
+ * SetVirtualAddressMap(), it is discarded.
+ *
+ * However, some boot services regions contain data that is required
+ * by drivers, so we need to track which memory ranges can never be
+ * freed. This is done by tagging those regions with the
+ * EFI_MEMORY_RUNTIME attribute.
+ *
+ * Any driver that wants to mark a region as reserved must use
+ * efi_mem_reserve() which will insert a new EFI memory descriptor
+ * into efi.memmap (splitting existing regions if necessary) and tag
+ * it with EFI_MEMORY_RUNTIME.
+ */
+void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size)
+{
+	struct efi_memory_map_data data = { 0 };
+	struct efi_mem_range mr;
+	efi_memory_desc_t md;
+	int num_entries;
+	void *new;
+
+	if (efi_mem_desc_lookup(addr, &md) ||
+	    md.type != EFI_BOOT_SERVICES_DATA) {
+		pr_err("Failed to lookup EFI memory descriptor for %pa\n", &addr);
+		return;
+	}
+
+	if (addr + size > md.phys_addr + (md.num_pages << EFI_PAGE_SHIFT)) {
+		pr_err("Region spans EFI memory descriptors, %pa\n", &addr);
+		return;
+	}
+
+	size += addr % EFI_PAGE_SIZE;
+	size = round_up(size, EFI_PAGE_SIZE);
+	addr = round_down(addr, EFI_PAGE_SIZE);
+
+	mr.range.start = addr;
+	mr.range.end = addr + size - 1;
+	mr.attribute = md.attribute | EFI_MEMORY_RUNTIME;
+
+	num_entries = efi_memmap_split_count(&md, &mr.range);
+	num_entries += efi.memmap.nr_map;
+
+	if (efi_memmap_alloc(num_entries, &data) != 0) {
+		pr_err("Could not allocate boot services memmap\n");
+		return;
+	}
+
+	new = early_memremap_prot(data.phys_map, data.size,
+				  pgprot_val(pgprot_encrypted(FIXMAP_PAGE_NORMAL)));
+	if (!new) {
+		pr_err("Failed to map new boot services memmap\n");
+		return;
+	}
+
+	efi_memmap_insert(&efi.memmap, new, &mr);
+	early_memunmap(new, data.size);
+
+	efi_memmap_install(&data);
+	e820__range_update(addr, size, E820_TYPE_RAM, E820_TYPE_RESERVED);
+	e820__update_table(e820_table);
+}
+
+/*
+ * Helper function for efi_reserve_boot_services() to figure out if we
+ * can free regions in efi_free_boot_services().
+ *
+ * Use this function to ensure we do not free regions owned by somebody
+ * else. We must only reserve (and then free) regions:
+ *
+ * - Not within any part of the kernel
+ * - Not the BIOS reserved area (E820_TYPE_RESERVED, E820_TYPE_NVS, etc)
+ */
+static __init bool can_free_region(u64 start, u64 size)
+{
+	if (start + size > __pa_symbol(_text) && start <= __pa_symbol(_end))
+		return false;
+
+	if (!e820__mapped_all(start, start+size, E820_TYPE_RAM))
+		return false;
+
+	return true;
+}
+
+void __init efi_reserve_boot_services(void)
+{
+	efi_memory_desc_t *md;
+
+	if (!efi_enabled(EFI_MEMMAP))
+		return;
+
+	for_each_efi_memory_desc(md) {
+		u64 start = md->phys_addr;
+		u64 size = md->num_pages << EFI_PAGE_SHIFT;
+		bool already_reserved;
+
+		if (md->type != EFI_BOOT_SERVICES_CODE &&
+		    md->type != EFI_BOOT_SERVICES_DATA)
+			continue;
+
+		already_reserved = memblock_is_region_reserved(start, size);
+
+		/*
+		 * Because the following memblock_reserve() is paired
+		 * with memblock_free_late() for this region in
+		 * efi_free_boot_services(), we must be extremely
+		 * careful not to reserve, and subsequently free,
+		 * critical regions of memory (like the kernel image) or
+		 * those regions that somebody else has already
+		 * reserved.
+		 *
+		 * A good example of a critical region that must not be
+		 * freed is page zero (first 4Kb of memory), which may
+		 * contain boot services code/data but is marked
+		 * E820_TYPE_RESERVED by trim_bios_range().
+		 */
+		if (!already_reserved) {
+			memblock_reserve(start, size);
+
+			/*
+			 * If we are the first to reserve the region, no
+			 * one else cares about it. We own it and can
+			 * free it later.
+			 */
+			if (can_free_region(start, size))
+				continue;
+		}
+
+		/*
+		 * We don't own the region. We must not free it.
+		 *
+		 * Setting this bit for a boot services region really
+		 * doesn't make sense as far as the firmware is
+		 * concerned, but it does provide us with a way to tag
+		 * those regions that must not be paired with
+		 * memblock_free_late().
+		 */
+		md->attribute |= EFI_MEMORY_RUNTIME;
+	}
+}
+
+/*
+ * Apart from having VA mappings for EFI boot services code/data regions,
+ * (duplicate) 1:1 mappings were also created as a quirk for buggy firmware. So,
+ * unmap both 1:1 and VA mappings.
+ */
+static void __init efi_unmap_pages(efi_memory_desc_t *md)
+{
+	pgd_t *pgd = efi_mm.pgd;
+	u64 pa = md->phys_addr;
+	u64 va = md->virt_addr;
+
+	/*
+	 * EFI mixed mode has all RAM mapped to access arguments while making
+	 * EFI runtime calls, hence don't unmap EFI boot services code/data
+	 * regions.
+	 */
+	if (efi_is_mixed())
+		return;
+
+	if (kernel_unmap_pages_in_pgd(pgd, pa, md->num_pages))
+		pr_err("Failed to unmap 1:1 mapping for 0x%llx\n", pa);
+
+	if (kernel_unmap_pages_in_pgd(pgd, va, md->num_pages))
+		pr_err("Failed to unmap VA mapping for 0x%llx\n", va);
+}
+
+void __init efi_free_boot_services(void)
+{
+	struct efi_memory_map_data data = { 0 };
+	efi_memory_desc_t *md;
+	int num_entries = 0;
+	void *new, *new_md;
+
+	/* Keep all regions for /sys/kernel/debug/efi */
+	if (efi_enabled(EFI_DBG))
+		return;
+
+	for_each_efi_memory_desc(md) {
+		unsigned long long start = md->phys_addr;
+		unsigned long long size = md->num_pages << EFI_PAGE_SHIFT;
+		size_t rm_size;
+
+		if (md->type != EFI_BOOT_SERVICES_CODE &&
+		    md->type != EFI_BOOT_SERVICES_DATA) {
+			num_entries++;
+			continue;
+		}
+
+		/* Do not free, someone else owns it: */
+		if (md->attribute & EFI_MEMORY_RUNTIME) {
+			num_entries++;
+			continue;
+		}
+
+		/*
+		 * Before calling set_virtual_address_map(), EFI boot services
+		 * code/data regions were mapped as a quirk for buggy firmware.
+		 * Unmap them from efi_pgd before freeing them up.
+		 */
+		efi_unmap_pages(md);
+
+		/*
+		 * Nasty quirk: if all sub-1MB memory is used for boot
+		 * services, we can get here without having allocated the
+		 * real mode trampoline.  It's too late to hand boot services
+		 * memory back to the memblock allocator, so instead
+		 * try to manually allocate the trampoline if needed.
+		 *
+		 * I've seen this on a Dell XPS 13 9350 with firmware
+		 * 1.4.4 with SGX enabled booting Linux via Fedora 24's
+		 * grub2-efi on a hard disk.  (And no, I don't know why
+		 * this happened, but Linux should still try to boot rather
+		 * panicing early.)
+		 */
+		rm_size = real_mode_size_needed();
+		if (rm_size && (start + rm_size) < (1<<20) && size >= rm_size) {
+			set_real_mode_mem(start);
+			start += rm_size;
+			size -= rm_size;
+		}
+
+		memblock_free_late(start, size);
+	}
+
+	if (!num_entries)
+		return;
+
+	if (efi_memmap_alloc(num_entries, &data) != 0) {
+		pr_err("Failed to allocate new EFI memmap\n");
+		return;
+	}
+
+	new = memremap(data.phys_map, data.size, MEMREMAP_WB);
+	if (!new) {
+		pr_err("Failed to map new EFI memmap\n");
+		return;
+	}
+
+	/*
+	 * Build a new EFI memmap that excludes any boot services
+	 * regions that are not tagged EFI_MEMORY_RUNTIME, since those
+	 * regions have now been freed.
+	 */
+	new_md = new;
+	for_each_efi_memory_desc(md) {
+		if (!(md->attribute & EFI_MEMORY_RUNTIME) &&
+		    (md->type == EFI_BOOT_SERVICES_CODE ||
+		     md->type == EFI_BOOT_SERVICES_DATA))
+			continue;
+
+		memcpy(new_md, md, efi.memmap.desc_size);
+		new_md += efi.memmap.desc_size;
+	}
+
+	memunmap(new);
+
+	if (efi_memmap_install(&data) != 0) {
+		pr_err("Could not install new EFI memmap\n");
+		return;
+	}
+}
+
+/*
+ * A number of config table entries get remapped to virtual addresses
+ * after entering EFI virtual mode. However, the kexec kernel requires
+ * their physical addresses therefore we pass them via setup_data and
+ * correct those entries to their respective physical addresses here.
+ *
+ * Currently only handles smbios which is necessary for some firmware
+ * implementation.
+ */
+int __init efi_reuse_config(u64 tables, int nr_tables)
+{
+	int i, sz, ret = 0;
+	void *p, *tablep;
+	struct efi_setup_data *data;
+
+	if (nr_tables == 0)
+		return 0;
+
+	if (!efi_setup)
+		return 0;
+
+	if (!efi_enabled(EFI_64BIT))
+		return 0;
+
+	data = early_memremap(efi_setup, sizeof(*data));
+	if (!data) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	if (!data->smbios)
+		goto out_memremap;
+
+	sz = sizeof(efi_config_table_64_t);
+
+	p = tablep = early_memremap(tables, nr_tables * sz);
+	if (!p) {
+		pr_err("Could not map Configuration table!\n");
+		ret = -ENOMEM;
+		goto out_memremap;
+	}
+
+	for (i = 0; i < nr_tables; i++) {
+		efi_guid_t guid;
+
+		guid = ((efi_config_table_64_t *)p)->guid;
+
+		if (!efi_guidcmp(guid, SMBIOS_TABLE_GUID))
+			((efi_config_table_64_t *)p)->table = data->smbios;
+		p += sz;
+	}
+	early_memunmap(tablep, nr_tables * sz);
+
+out_memremap:
+	early_memunmap(data, sizeof(*data));
+out:
+	return ret;
+}
+
+void __init efi_apply_memmap_quirks(void)
+{
+	/*
+	 * Once setup is done earlier, unmap the EFI memory map on mismatched
+	 * firmware/kernel architectures since there is no support for runtime
+	 * services.
+	 */
+	if (!efi_runtime_supported()) {
+		pr_info("Setup done, disabling due to 32/64-bit mismatch\n");
+		efi_memmap_unmap();
+	}
+}
+
+/*
+ * For most modern platforms the preferred method of powering off is via
+ * ACPI. However, there are some that are known to require the use of
+ * EFI runtime services and for which ACPI does not work at all.
+ *
+ * Using EFI is a last resort, to be used only if no other option
+ * exists.
+ */
+bool efi_reboot_required(void)
+{
+	if (!acpi_gbl_reduced_hardware)
+		return false;
+
+	efi_reboot_quirk_mode = EFI_RESET_WARM;
+	return true;
+}
+
+bool efi_poweroff_required(void)
+{
+	return acpi_gbl_reduced_hardware || acpi_no_s5;
+}
+
+#ifdef CONFIG_EFI_CAPSULE_QUIRK_QUARK_CSH
+
+static int qrk_capsule_setup_info(struct capsule_info *cap_info, void **pkbuff,
+				  size_t hdr_bytes)
+{
+	struct quark_security_header *csh = *pkbuff;
+
+	/* Only process data block that is larger than the security header */
+	if (hdr_bytes < sizeof(struct quark_security_header))
+		return 0;
+
+	if (csh->csh_signature != QUARK_CSH_SIGNATURE ||
+	    csh->headersize != QUARK_SECURITY_HEADER_SIZE)
+		return 1;
+
+	/* Only process data block if EFI header is included */
+	if (hdr_bytes < QUARK_SECURITY_HEADER_SIZE +
+			sizeof(efi_capsule_header_t))
+		return 0;
+
+	pr_debug("Quark security header detected\n");
+
+	if (csh->rsvd_next_header != 0) {
+		pr_err("multiple Quark security headers not supported\n");
+		return -EINVAL;
+	}
+
+	*pkbuff += csh->headersize;
+	cap_info->total_size = csh->headersize;
+
+	/*
+	 * Update the first page pointer to skip over the CSH header.
+	 */
+	cap_info->phys[0] += csh->headersize;
+
+	/*
+	 * cap_info->capsule should point at a virtual mapping of the entire
+	 * capsule, starting at the capsule header. Our image has the Quark
+	 * security header prepended, so we cannot rely on the default vmap()
+	 * mapping created by the generic capsule code.
+	 * Given that the Quark firmware does not appear to care about the
+	 * virtual mapping, let's just point cap_info->capsule at our copy
+	 * of the capsule header.
+	 */
+	cap_info->capsule = &cap_info->header;
+
+	return 1;
+}
+
+static const struct x86_cpu_id efi_capsule_quirk_ids[] = {
+	X86_MATCH_VENDOR_FAM_MODEL(INTEL, 5, INTEL_FAM5_QUARK_X1000,
+				   &qrk_capsule_setup_info),
+	{ }
+};
+
+int efi_capsule_setup_info(struct capsule_info *cap_info, void *kbuff,
+			   size_t hdr_bytes)
+{
+	int (*quirk_handler)(struct capsule_info *, void **, size_t);
+	const struct x86_cpu_id *id;
+	int ret;
+
+	if (hdr_bytes < sizeof(efi_capsule_header_t))
+		return 0;
+
+	cap_info->total_size = 0;
+
+	id = x86_match_cpu(efi_capsule_quirk_ids);
+	if (id) {
+		/*
+		 * The quirk handler is supposed to return
+		 *  - a value > 0 if the setup should continue, after advancing
+		 *    kbuff as needed
+		 *  - 0 if not enough hdr_bytes are available yet
+		 *  - a negative error code otherwise
+		 */
+		quirk_handler = (typeof(quirk_handler))id->driver_data;
+		ret = quirk_handler(cap_info, &kbuff, hdr_bytes);
+		if (ret <= 0)
+			return ret;
+	}
+
+	memcpy(&cap_info->header, kbuff, sizeof(cap_info->header));
+
+	cap_info->total_size += cap_info->header.imagesize;
+
+	return __efi_capsule_setup_info(cap_info);
+}
+
+#endif
+
+/*
+ * If any access by any efi runtime service causes a page fault, then,
+ * 1. If it's efi_reset_system(), reboot through BIOS.
+ * 2. If any other efi runtime service, then
+ *    a. Return error status to the efi caller process.
+ *    b. Disable EFI Runtime Services forever and
+ *    c. Freeze efi_rts_wq and schedule new process.
+ *
+ * @return: Returns, if the page fault is not handled. This function
+ * will never return if the page fault is handled successfully.
+ */
+void efi_recover_from_page_fault(unsigned long phys_addr)
+{
+	if (!IS_ENABLED(CONFIG_X86_64))
+		return;
+
+	/*
+	 * Make sure that an efi runtime service caused the page fault.
+	 */
+	if (efi_rts_work.efi_rts_id == EFI_NONE)
+		return;
+
+	/*
+	 * Address range 0x0000 - 0x0fff is always mapped in the efi_pgd, so
+	 * page faulting on these addresses isn't expected.
+	 */
+	if (phys_addr <= 0x0fff)
+		return;
+
+	/*
+	 * Print stack trace as it might be useful to know which EFI Runtime
+	 * Service is buggy.
+	 */
+	WARN(1, FW_BUG "Page fault caused by firmware at PA: 0x%lx\n",
+	     phys_addr);
+
+	/*
+	 * Buggy efi_reset_system() is handled differently from other EFI
+	 * Runtime Services as it doesn't use efi_rts_wq. Although,
+	 * native_machine_emergency_restart() says that machine_real_restart()
+	 * could fail, it's better not to compilcate this fault handler
+	 * because this case occurs *very* rarely and hence could be improved
+	 * on a need by basis.
+	 */
+	if (efi_rts_work.efi_rts_id == EFI_RESET_SYSTEM) {
+		pr_info("efi_reset_system() buggy! Reboot through BIOS\n");
+		machine_real_restart(MRR_BIOS);
+		return;
+	}
+
+	/*
+	 * Before calling EFI Runtime Service, the kernel has switched the
+	 * calling process to efi_mm. Hence, switch back to task_mm.
+	 */
+	arch_efi_call_virt_teardown();
+
+	/* Signal error status to the efi caller process */
+	efi_rts_work.status = EFI_ABORTED;
+	complete(&efi_rts_work.efi_rts_comp);
+
+	clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
+	pr_info("Froze efi_rts_wq and disabled EFI Runtime Services\n");
+
+	/*
+	 * Call schedule() in an infinite loop, so that any spurious wake ups
+	 * will never run efi_rts_wq again.
+	 */
+	for (;;) {
+		set_current_state(TASK_IDLE);
+		schedule();
+	}
+
+	return;
+}