linux/arch/arm64/kernel/efi.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Extensible Firmware Interface
 *
 * Based on Extensible Firmware Interface Specification version 2.4
 *
 * Copyright (C) 2013, 2014 Linaro Ltd.
 */

#include <linux/efi.h>
#include <linux/init.h>
#include <linux/kmemleak.h>
#include <linux/kthread.h>
#include <linux/screen_info.h>
#include <linux/vmalloc.h>

#include <asm/efi.h>
#include <asm/stacktrace.h>
#include <asm/vmap_stack.h>

static bool region_is_misaligned(const efi_memory_desc_t *md)
{
	if (PAGE_SIZE == EFI_PAGE_SIZE)
		return false;
	return !PAGE_ALIGNED(md->phys_addr) ||
	       !PAGE_ALIGNED(md->num_pages << EFI_PAGE_SHIFT);
}

/*
 * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
 * executable, everything else can be mapped with the XN bits
 * set. Also take the new (optional) RO/XP bits into account.
 */
static __init ptdesc_t create_mapping_protection(efi_memory_desc_t *md)
{
	u64 attr = md->attribute;
	u32 type = md->type;

	if (type == EFI_MEMORY_MAPPED_IO) {
		pgprot_t prot = __pgprot(PROT_DEVICE_nGnRE);

		if (arm64_is_protected_mmio(md->phys_addr,
					    md->num_pages << EFI_PAGE_SHIFT))
			prot = pgprot_encrypted(prot);
		else
			prot = pgprot_decrypted(prot);
		return pgprot_val(prot);
	}

	if (region_is_misaligned(md)) {
		static bool __initdata code_is_misaligned;

		/*
		 * Regions that are not aligned to the OS page size cannot be
		 * mapped with strict permissions, as those might interfere
		 * with the permissions that are needed by the adjacent
		 * region's mapping. However, if we haven't encountered any
		 * misaligned runtime code regions so far, we can safely use
		 * non-executable permissions for non-code regions.
		 */
		code_is_misaligned |= (type == EFI_RUNTIME_SERVICES_CODE);

		return code_is_misaligned ? pgprot_val(PAGE_KERNEL_EXEC)
					  : pgprot_val(PAGE_KERNEL);
	}

	/* R-- */
	if ((attr & (EFI_MEMORY_XP | EFI_MEMORY_RO)) ==
	    (EFI_MEMORY_XP | EFI_MEMORY_RO))
		return pgprot_val(PAGE_KERNEL_RO);

	/* R-X */
	if (attr & EFI_MEMORY_RO)
		return pgprot_val(PAGE_KERNEL_ROX);

	/* RW- */
	if (((attr & (EFI_MEMORY_RP | EFI_MEMORY_WP | EFI_MEMORY_XP)) ==
	     EFI_MEMORY_XP) ||
	    type != EFI_RUNTIME_SERVICES_CODE)
		return pgprot_val(PAGE_KERNEL);

	/* RWX */
	return pgprot_val(PAGE_KERNEL_EXEC);
}

int __init efi_create_mapping(struct mm_struct *mm, efi_memory_desc_t *md)
{
	ptdesc_t prot_val = create_mapping_protection(md);
	bool page_mappings_only = (md->type == EFI_RUNTIME_SERVICES_CODE ||
				   md->type == EFI_RUNTIME_SERVICES_DATA);

	/*
	 * If this region is not aligned to the page size used by the OS, the
	 * mapping will be rounded outwards, and may end up sharing a page
	 * frame with an adjacent runtime memory region. Given that the page
	 * table descriptor covering the shared page will be rewritten when the
	 * adjacent region gets mapped, we must avoid block mappings here so we
	 * don't have to worry about splitting them when that happens.
	 */
	if (region_is_misaligned(md))
		page_mappings_only = true;

	create_pgd_mapping(mm, md->phys_addr, md->virt_addr,
			   md->num_pages << EFI_PAGE_SHIFT,
			   __pgprot(prot_val | PTE_NG), page_mappings_only);
	return 0;
}

struct set_perm_data {
	const efi_memory_desc_t	*md;
	bool			has_bti;
};

static int __init set_permissions(pte_t *ptep, unsigned long addr, void *data)
{
	struct set_perm_data *spd = data;
	const efi_memory_desc_t *md = spd->md;
	pte_t pte = __ptep_get(ptep);

	if (md->attribute & EFI_MEMORY_RO)
		pte = set_pte_bit(pte, __pgprot(PTE_RDONLY));
	if (md->attribute & EFI_MEMORY_XP)
		pte = set_pte_bit(pte, __pgprot(PTE_PXN));
	else if (system_supports_bti_kernel() && spd->has_bti)
		pte = set_pte_bit(pte, __pgprot(PTE_GP));
	__set_pte(ptep, pte);
	return 0;
}

int __init efi_set_mapping_permissions(struct mm_struct *mm,
				       efi_memory_desc_t *md,
				       bool has_bti)
{
	struct set_perm_data data = { md, has_bti };

	BUG_ON(md->type != EFI_RUNTIME_SERVICES_CODE &&
	       md->type != EFI_RUNTIME_SERVICES_DATA);

	if (region_is_misaligned(md))
		return 0;

	/*
	 * Calling apply_to_page_range() is only safe on regions that are
	 * guaranteed to be mapped down to pages. Since we are only called
	 * for regions that have been mapped using efi_create_mapping() above
	 * (and this is checked by the generic Memory Attributes table parsing
	 * routines), there is no need to check that again here.
	 */
	return apply_to_page_range(mm, md->virt_addr,
				   md->num_pages << EFI_PAGE_SHIFT,
				   set_permissions, &data);
}

/*
 * UpdateCapsule() depends on the system being shutdown via
 * ResetSystem().
 */
bool efi_poweroff_required(void)
{
	return efi_enabled(EFI_RUNTIME_SERVICES);
}

asmlinkage efi_status_t efi_handle_corrupted_x18(efi_status_t s, const char *f)
{
	pr_err_ratelimited(FW_BUG "register x18 corrupted by EFI %s\n", f);
	return s;
}

void arch_efi_call_virt_setup(void)
{
	efi_runtime_assert_lock_held();

	if (preemptible() && (current->flags & PF_KTHREAD)) {
		/*
		 * Disable migration to ensure that a preempted EFI runtime
		 * service call will be resumed on the same CPU. This avoids
		 * potential issues with EFI runtime calls that are preempted
		 * while polling for an asynchronous completion of a secure
		 * firmware call, which may not permit the CPU to change.
		 */
		migrate_disable();
		kthread_use_mm(&efi_mm);
	} else {
		efi_virtmap_load();
	}

	/*
	 * Enable access to the valid TTBR0_EL1 and invoke the errata
	 * workaround directly since there is no return from exception when
	 * invoking the EFI run-time services.
	 */
	uaccess_ttbr0_enable();
	post_ttbr_update_workaround();

	__efi_fpsimd_begin();
}

void arch_efi_call_virt_teardown(void)
{
	__efi_fpsimd_end();

	/*
	 * Defer the switch to the current thread's TTBR0_EL1 until
	 * uaccess_enable(). Do so before efi_virtmap_unload() updates the
	 * saved TTBR0 value, so the userland page tables are not activated
	 * inadvertently over the back of an exception.
	 */
	uaccess_ttbr0_disable();

	if (preemptible() && (current->flags & PF_KTHREAD)) {
		kthread_unuse_mm(&efi_mm);
		migrate_enable();
	} else {
		efi_virtmap_unload();
	}
}

asmlinkage u64 *efi_rt_stack_top __ro_after_init;

asmlinkage efi_status_t __efi_rt_asm_recover(void);

bool efi_runtime_fixup_exception(struct pt_regs *regs, const char *msg)
{
	 /* Check whether the exception occurred while running the firmware */
	if (!current_in_efi() || regs->pc >= TASK_SIZE_64)
		return false;

	pr_err(FW_BUG "Unable to handle %s in EFI runtime service\n", msg);
	add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);
	clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);

	regs->regs[0]	= EFI_ABORTED;
	regs->regs[30]	= efi_rt_stack_top[-1];
	regs->pc	= (u64)__efi_rt_asm_recover;

	if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK))
		regs->regs[18] = efi_rt_stack_top[-2];

	return true;
}

/* EFI requires 8 KiB of stack space for runtime services */
static_assert(THREAD_SIZE >= SZ_8K);

static int __init arm64_efi_rt_init(void)
{
	void *p;

	if (!efi_enabled(EFI_RUNTIME_SERVICES))
		return 0;

	p = arch_alloc_vmap_stack(THREAD_SIZE, NUMA_NO_NODE);
	if (!p) {
		pr_warn("Failed to allocate EFI runtime stack\n");
		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
		return -ENOMEM;
	}

	kmemleak_not_leak(p);
	efi_rt_stack_top = p + THREAD_SIZE;
	return 0;
}
core_initcall(arm64_efi_rt_init);