arch/arm64/kernel/vdso.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * VDSO implementations.
 *
 * Copyright (C) 2012 ARM Limited
 *
 * Author: Will Deacon <will.deacon@arm.com>
 */

#include <linux/cache.h>
#include <linux/clocksource.h>
#include <linux/elf.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/signal.h>
#include <linux/slab.h>
#include <linux/time_namespace.h>
#include <linux/timekeeper_internal.h>
#include <linux/vmalloc.h>
#include <vdso/datapage.h>
#include <vdso/helpers.h>
#include <vdso/vsyscall.h>

#include <asm/cacheflush.h>
#include <asm/signal32.h>
#include <asm/vdso.h>

extern char vdso_start[], vdso_end[];
extern char vdso32_start[], vdso32_end[];

enum vdso_abi {
	VDSO_ABI_AA64,
	VDSO_ABI_AA32,
};

enum vvar_pages {
	VVAR_DATA_PAGE_OFFSET,
	VVAR_TIMENS_PAGE_OFFSET,
	VVAR_NR_PAGES,
};

struct vdso_abi_info {
	const char *name;
	const char *vdso_code_start;
	const char *vdso_code_end;
	unsigned long vdso_pages;
	/* Data Mapping */
	struct vm_special_mapping *dm;
	/* Code Mapping */
	struct vm_special_mapping *cm;
};

static struct vdso_abi_info vdso_info[] __ro_after_init = {
	[VDSO_ABI_AA64] = {
		.name = "vdso",
		.vdso_code_start = vdso_start,
		.vdso_code_end = vdso_end,
	},
#ifdef CONFIG_COMPAT_VDSO
	[VDSO_ABI_AA32] = {
		.name = "vdso32",
		.vdso_code_start = vdso32_start,
		.vdso_code_end = vdso32_end,
	},
#endif /* CONFIG_COMPAT_VDSO */
};

/*
 * The vDSO data page.
 */
static union {
	struct vdso_data	data[CS_BASES];
	u8			page[PAGE_SIZE];
} vdso_data_store __page_aligned_data;
struct vdso_data *vdso_data = vdso_data_store.data;

static int vdso_mremap(const struct vm_special_mapping *sm,
		struct vm_area_struct *new_vma)
{
	current->mm->context.vdso = (void *)new_vma->vm_start;

	return 0;
}

static int __vdso_init(enum vdso_abi abi)
{
	int i;
	struct page **vdso_pagelist;
	unsigned long pfn;

	if (memcmp(vdso_info[abi].vdso_code_start, "\177ELF", 4)) {
		pr_err("vDSO is not a valid ELF object!\n");
		return -EINVAL;
	}

	vdso_info[abi].vdso_pages = (
			vdso_info[abi].vdso_code_end -
			vdso_info[abi].vdso_code_start) >>
			PAGE_SHIFT;

	vdso_pagelist = kcalloc(vdso_info[abi].vdso_pages,
				sizeof(struct page *),
				GFP_KERNEL);
	if (vdso_pagelist == NULL)
		return -ENOMEM;

	/* Grab the vDSO code pages. */
	pfn = sym_to_pfn(vdso_info[abi].vdso_code_start);

	for (i = 0; i < vdso_info[abi].vdso_pages; i++)
		vdso_pagelist[i] = pfn_to_page(pfn + i);

	vdso_info[abi].cm->pages = vdso_pagelist;

	return 0;
}

#ifdef CONFIG_TIME_NS
struct vdso_data *arch_get_vdso_data(void *vvar_page)
{
	return (struct vdso_data *)(vvar_page);
}

/*
 * The vvar mapping contains data for a specific time namespace, so when a task
 * changes namespace we must unmap its vvar data for the old namespace.
 * Subsequent faults will map in data for the new namespace.
 *
 * For more details see timens_setup_vdso_data().
 */
int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
{
	struct mm_struct *mm = task->mm;
	struct vm_area_struct *vma;

	mmap_read_lock(mm);

	for (vma = mm->mmap; vma; vma = vma->vm_next) {
		unsigned long size = vma->vm_end - vma->vm_start;

		if (vma_is_special_mapping(vma, vdso_info[VDSO_ABI_AA64].dm))
			zap_page_range(vma, vma->vm_start, size);
#ifdef CONFIG_COMPAT_VDSO
		if (vma_is_special_mapping(vma, vdso_info[VDSO_ABI_AA32].dm))
			zap_page_range(vma, vma->vm_start, size);
#endif
	}

	mmap_read_unlock(mm);
	return 0;
}

static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
{
	if (likely(vma->vm_mm == current->mm))
		return current->nsproxy->time_ns->vvar_page;

	/*
	 * VM_PFNMAP | VM_IO protect .fault() handler from being called
	 * through interfaces like /proc/$pid/mem or
	 * process_vm_{readv,writev}() as long as there's no .access()
	 * in special_mapping_vmops.
	 * For more details check_vma_flags() and __access_remote_vm()
	 */
	WARN(1, "vvar_page accessed remotely");

	return NULL;
}
#else
static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
{
	return NULL;
}
#endif

static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
			     struct vm_area_struct *vma, struct vm_fault *vmf)
{
	struct page *timens_page = find_timens_vvar_page(vma);
	unsigned long pfn;

	switch (vmf->pgoff) {
	case VVAR_DATA_PAGE_OFFSET:
		if (timens_page)
			pfn = page_to_pfn(timens_page);
		else
			pfn = sym_to_pfn(vdso_data);
		break;
#ifdef CONFIG_TIME_NS
	case VVAR_TIMENS_PAGE_OFFSET:
		/*
		 * If a task belongs to a time namespace then a namespace
		 * specific VVAR is mapped with the VVAR_DATA_PAGE_OFFSET and
		 * the real VVAR page is mapped with the VVAR_TIMENS_PAGE_OFFSET
		 * offset.
		 * See also the comment near timens_setup_vdso_data().
		 */
		if (!timens_page)
			return VM_FAULT_SIGBUS;
		pfn = sym_to_pfn(vdso_data);
		break;
#endif /* CONFIG_TIME_NS */
	default:
		return VM_FAULT_SIGBUS;
	}

	return vmf_insert_pfn(vma, vmf->address, pfn);
}

static int __setup_additional_pages(enum vdso_abi abi,
				    struct mm_struct *mm,
				    struct linux_binprm *bprm,
				    int uses_interp)
{
	unsigned long vdso_base, vdso_text_len, vdso_mapping_len;
	unsigned long gp_flags = 0;
	void *ret;

	BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);

	vdso_text_len = vdso_info[abi].vdso_pages << PAGE_SHIFT;
	/* Be sure to map the data page */
	vdso_mapping_len = vdso_text_len + VVAR_NR_PAGES * PAGE_SIZE;

	vdso_base = get_unmapped_area(NULL, 0, vdso_mapping_len, 0, 0);
	if (IS_ERR_VALUE(vdso_base)) {
		ret = ERR_PTR(vdso_base);
		goto up_fail;
	}

	ret = _install_special_mapping(mm, vdso_base, VVAR_NR_PAGES * PAGE_SIZE,
				       VM_READ|VM_MAYREAD|VM_PFNMAP,
				       vdso_info[abi].dm);
	if (IS_ERR(ret))
		goto up_fail;

	if (IS_ENABLED(CONFIG_ARM64_BTI_KERNEL) && system_supports_bti())
		gp_flags = VM_ARM64_BTI;

	vdso_base += VVAR_NR_PAGES * PAGE_SIZE;
	mm->context.vdso = (void *)vdso_base;
	ret = _install_special_mapping(mm, vdso_base, vdso_text_len,
				       VM_READ|VM_EXEC|gp_flags|
				       VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
				       vdso_info[abi].cm);
	if (IS_ERR(ret))
		goto up_fail;

	return 0;

up_fail:
	mm->context.vdso = NULL;
	return PTR_ERR(ret);
}

#ifdef CONFIG_COMPAT
/*
 * Create and map the vectors page for AArch32 tasks.
 */
enum aarch32_map {
	AA32_MAP_VECTORS, /* kuser helpers */
	AA32_MAP_SIGPAGE,
	AA32_MAP_VVAR,
	AA32_MAP_VDSO,
};

static struct page *aarch32_vectors_page __ro_after_init;
static struct page *aarch32_sig_page __ro_after_init;

static struct vm_special_mapping aarch32_vdso_maps[] = {
	[AA32_MAP_VECTORS] = {
		.name	= "[vectors]", /* ABI */
		.pages	= &aarch32_vectors_page,
	},
	[AA32_MAP_SIGPAGE] = {
		.name	= "[sigpage]", /* ABI */
		.pages	= &aarch32_sig_page,
	},
	[AA32_MAP_VVAR] = {
		.name = "[vvar]",
		.fault = vvar_fault,
	},
	[AA32_MAP_VDSO] = {
		.name = "[vdso]",
		.mremap = vdso_mremap,
	},
};

static int aarch32_alloc_kuser_vdso_page(void)
{
	extern char __kuser_helper_start[], __kuser_helper_end[];
	int kuser_sz = __kuser_helper_end - __kuser_helper_start;
	unsigned long vdso_page;

	if (!IS_ENABLED(CONFIG_KUSER_HELPERS))
		return 0;

	vdso_page = get_zeroed_page(GFP_ATOMIC);
	if (!vdso_page)
		return -ENOMEM;

	memcpy((void *)(vdso_page + 0x1000 - kuser_sz), __kuser_helper_start,
	       kuser_sz);
	aarch32_vectors_page = virt_to_page(vdso_page);
	flush_dcache_page(aarch32_vectors_page);
	return 0;
}

static int aarch32_alloc_sigpage(void)
{
	extern char __aarch32_sigret_code_start[], __aarch32_sigret_code_end[];
	int sigret_sz = __aarch32_sigret_code_end - __aarch32_sigret_code_start;
	unsigned long sigpage;

	sigpage = get_zeroed_page(GFP_ATOMIC);
	if (!sigpage)
		return -ENOMEM;

	memcpy((void *)sigpage, __aarch32_sigret_code_start, sigret_sz);
	aarch32_sig_page = virt_to_page(sigpage);
	flush_dcache_page(aarch32_sig_page);
	return 0;
}

static int __aarch32_alloc_vdso_pages(void)
{

	if (!IS_ENABLED(CONFIG_COMPAT_VDSO))
		return 0;

	vdso_info[VDSO_ABI_AA32].dm = &aarch32_vdso_maps[AA32_MAP_VVAR];
	vdso_info[VDSO_ABI_AA32].cm = &aarch32_vdso_maps[AA32_MAP_VDSO];

	return __vdso_init(VDSO_ABI_AA32);
}

static int __init aarch32_alloc_vdso_pages(void)
{
	int ret;

	ret = __aarch32_alloc_vdso_pages();
	if (ret)
		return ret;

	ret = aarch32_alloc_sigpage();
	if (ret)
		return ret;

	return aarch32_alloc_kuser_vdso_page();
}
arch_initcall(aarch32_alloc_vdso_pages);

static int aarch32_kuser_helpers_setup(struct mm_struct *mm)
{
	void *ret;

	if (!IS_ENABLED(CONFIG_KUSER_HELPERS))
		return 0;

	/*
	 * Avoid VM_MAYWRITE for compatibility with arch/arm/, where it's
	 * not safe to CoW the page containing the CPU exception vectors.
	 */
	ret = _install_special_mapping(mm, AARCH32_VECTORS_BASE, PAGE_SIZE,
				       VM_READ | VM_EXEC |
				       VM_MAYREAD | VM_MAYEXEC,
				       &aarch32_vdso_maps[AA32_MAP_VECTORS]);

	return PTR_ERR_OR_ZERO(ret);
}

static int aarch32_sigreturn_setup(struct mm_struct *mm)
{
	unsigned long addr;
	void *ret;

	addr = get_unmapped_area(NULL, 0, PAGE_SIZE, 0, 0);
	if (IS_ERR_VALUE(addr)) {
		ret = ERR_PTR(addr);
		goto out;
	}

	/*
	 * VM_MAYWRITE is required to allow gdb to Copy-on-Write and
	 * set breakpoints.
	 */
	ret = _install_special_mapping(mm, addr, PAGE_SIZE,
				       VM_READ | VM_EXEC | VM_MAYREAD |
				       VM_MAYWRITE | VM_MAYEXEC,
				       &aarch32_vdso_maps[AA32_MAP_SIGPAGE]);
	if (IS_ERR(ret))
		goto out;

	mm->context.sigpage = (void *)addr;

out:
	return PTR_ERR_OR_ZERO(ret);
}

int aarch32_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
	struct mm_struct *mm = current->mm;
	int ret;

	if (mmap_write_lock_killable(mm))
		return -EINTR;

	ret = aarch32_kuser_helpers_setup(mm);
	if (ret)
		goto out;

	if (IS_ENABLED(CONFIG_COMPAT_VDSO)) {
		ret = __setup_additional_pages(VDSO_ABI_AA32, mm, bprm,
					       uses_interp);
		if (ret)
			goto out;
	}

	ret = aarch32_sigreturn_setup(mm);
out:
	mmap_write_unlock(mm);
	return ret;
}
#endif /* CONFIG_COMPAT */

enum aarch64_map {
	AA64_MAP_VVAR,
	AA64_MAP_VDSO,
};

static struct vm_special_mapping aarch64_vdso_maps[] __ro_after_init = {
	[AA64_MAP_VVAR] = {
		.name	= "[vvar]",
		.fault = vvar_fault,
	},
	[AA64_MAP_VDSO] = {
		.name	= "[vdso]",
		.mremap = vdso_mremap,
	},
};

static int __init vdso_init(void)
{
	vdso_info[VDSO_ABI_AA64].dm = &aarch64_vdso_maps[AA64_MAP_VVAR];
	vdso_info[VDSO_ABI_AA64].cm = &aarch64_vdso_maps[AA64_MAP_VDSO];

	return __vdso_init(VDSO_ABI_AA64);
}
arch_initcall(vdso_init);

int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
	struct mm_struct *mm = current->mm;
	int ret;

	if (mmap_write_lock_killable(mm))
		return -EINTR;

	ret = __setup_additional_pages(VDSO_ABI_AA64, mm, bprm, uses_interp);
	mmap_write_unlock(mm);

	return ret;
}