arch/arm/kernel/vdso.c - arm/linux - Git at Google

 /*
  * Adapted from arm64 version.
  *
  * Copyright (C) 2012 ARM Limited
  * Copyright (C) 2015 Mentor Graphics Corporation.
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 2 as
  * published by the Free Software Foundation.
  *
  * This program is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */

 #include <linux/cache.h>
 #include <linux/elf.h>
 #include <linux/err.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/of.h>
 #include <linux/printk.h>
 #include <linux/slab.h>
 #include <linux/timekeeper_internal.h>
 #include <linux/vmalloc.h>
 #include <asm/arch_timer.h>
 #include <asm/barrier.h>
 #include <asm/cacheflush.h>
 #include <asm/page.h>
 #include <asm/vdso.h>
 #include <asm/vdso_datapage.h>
 #include <clocksource/arm_arch_timer.h>

 #define MAX_SYMNAME	64

 static struct page **vdso_text_pagelist;

 /* Total number of pages needed for the data and text portions of the VDSO. */
 unsigned int vdso_total_pages __ro_after_init;

 /*
  * The VDSO data page.
  */
 static union vdso_data_store vdso_data_store __page_aligned_data;
 static struct vdso_data *vdso_data = &vdso_data_store.data;

 static struct page *vdso_data_page __ro_after_init;
 static const struct vm_special_mapping vdso_data_mapping = {
 	.name = "[vvar]",
 	.pages = &vdso_data_page,
 };

 static int vdso_mremap(const struct vm_special_mapping *sm,
 		struct vm_area_struct *new_vma)
 {
 	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
 	unsigned long vdso_size;

 	/* without VVAR page */
 	vdso_size = (vdso_total_pages - 1) << PAGE_SHIFT;

 	if (vdso_size != new_size)
 		return -EINVAL;

 	current->mm->context.vdso = new_vma->vm_start;

 	return 0;
 }

 static struct vm_special_mapping vdso_text_mapping __ro_after_init = {
 	.name = "[vdso]",
 	.mremap = vdso_mremap,
 };

 struct elfinfo {
 	Elf32_Ehdr	*hdr;		/* ptr to ELF */
 	Elf32_Sym	*dynsym;	/* ptr to .dynsym section */
 	unsigned long	dynsymsize;	/* size of .dynsym section */
 	char		*dynstr;	/* ptr to .dynstr section */
 };

 /* Cached result of boot-time check for whether the arch timer exists,
  * and if so, whether the virtual counter is useable.
  */
 static bool cntvct_ok __ro_after_init;

 static bool __init cntvct_functional(void)
 {
 	struct device_node *np;
 	bool ret = false;

 	if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
 		goto out;

 	/* The arm_arch_timer core should export
 	 * arch_timer_use_virtual or similar so we don't have to do
 	 * this.
 	 */
 	np = of_find_compatible_node(NULL, NULL, "arm,armv7-timer");
 	if (!np)
 		goto out_put;

 	if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
 		goto out_put;

 	ret = true;

 out_put:
 	of_node_put(np);
 out:
 	return ret;
 }

 static void * __init find_section(Elf32_Ehdr *ehdr, const char *name,
 				  unsigned long *size)
 {
 	Elf32_Shdr *sechdrs;
 	unsigned int i;
 	char *secnames;

 	/* Grab section headers and strings so we can tell who is who */
 	sechdrs = (void *)ehdr + ehdr->e_shoff;
 	secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;

 	/* Find the section they want */
 	for (i = 1; i < ehdr->e_shnum; i++) {
 		if (strcmp(secnames + sechdrs[i].sh_name, name) == 0) {
 			if (size)
 				*size = sechdrs[i].sh_size;
 			return (void *)ehdr + sechdrs[i].sh_offset;
 		}
 	}

 	if (size)
 		*size = 0;
 	return NULL;
 }

 static Elf32_Sym * __init find_symbol(struct elfinfo *lib, const char *symname)
 {
 	unsigned int i;

 	for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
 		char name[MAX_SYMNAME], *c;

 		if (lib->dynsym[i].st_name == 0)
 			continue;
 		strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
 			MAX_SYMNAME);
 		c = strchr(name, '@');
 		if (c)
 			*c = 0;
 		if (strcmp(symname, name) == 0)
 			return &lib->dynsym[i];
 	}
 	return NULL;
 }

 static void __init vdso_nullpatch_one(struct elfinfo *lib, const char *symname)
 {
 	Elf32_Sym *sym;

 	sym = find_symbol(lib, symname);
 	if (!sym)
 		return;

 	sym->st_name = 0;
 }

 static void __init patch_vdso(void *ehdr)
 {
 	struct elfinfo einfo;

 	einfo = (struct elfinfo) {
 		.hdr = ehdr,
 	};

 	einfo.dynsym = find_section(einfo.hdr, ".dynsym", &einfo.dynsymsize);
 	einfo.dynstr = find_section(einfo.hdr, ".dynstr", NULL);

 	/* If the virtual counter is absent or non-functional we don't
 	 * want programs to incur the slight additional overhead of
 	 * dispatching through the VDSO only to fall back to syscalls.
 	 */
 	if (!cntvct_ok) {
 		vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
 		vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
 	}
 }

 static int __init vdso_init(void)
 {
 	unsigned int text_pages;
 	int i;

 	if (memcmp(&vdso_start, "\177ELF", 4)) {
 		pr_err("VDSO is not a valid ELF object!\n");
 		return -ENOEXEC;
 	}

 	text_pages = (&vdso_end - &vdso_start) >> PAGE_SHIFT;
 	pr_debug("vdso: %i text pages at base %p\n", text_pages, &vdso_start);

 	/* Allocate the VDSO text pagelist */
 	vdso_text_pagelist = kcalloc(text_pages, sizeof(struct page *),
 				     GFP_KERNEL);
 	if (vdso_text_pagelist == NULL)
 		return -ENOMEM;

 	/* Grab the VDSO data page. */
 	vdso_data_page = virt_to_page(vdso_data);

 	/* Grab the VDSO text pages. */
 	for (i = 0; i < text_pages; i++) {
 		struct page *page;

 		page = virt_to_page(&vdso_start + i * PAGE_SIZE);
 		vdso_text_pagelist[i] = page;
 	}

 	vdso_text_mapping.pages = vdso_text_pagelist;

 	vdso_total_pages = 1; /* for the data/vvar page */
 	vdso_total_pages += text_pages;

 	cntvct_ok = cntvct_functional();

 	patch_vdso(&vdso_start);

 	return 0;
 }
 arch_initcall(vdso_init);

 static int install_vvar(struct mm_struct *mm, unsigned long addr)
 {
 	struct vm_area_struct *vma;

 	vma = _install_special_mapping(mm, addr, PAGE_SIZE,
 				       VM_READ | VM_MAYREAD,
 				       &vdso_data_mapping);

 	return PTR_ERR_OR_ZERO(vma);
 }

 /* assumes mmap_sem is write-locked */
 void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
 {
 	struct vm_area_struct *vma;
 	unsigned long len;

 	mm->context.vdso = 0;

 	if (vdso_text_pagelist == NULL)
 		return;

 	if (install_vvar(mm, addr))
 		return;

 	/* Account for vvar page. */
 	addr += PAGE_SIZE;
 	len = (vdso_total_pages - 1) << PAGE_SHIFT;

 	vma = _install_special_mapping(mm, addr, len,
 		VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
 		&vdso_text_mapping);

 	if (!IS_ERR(vma))
 		mm->context.vdso = addr;
 }

 static void vdso_write_begin(struct vdso_data *vdata)
 {
 	++vdso_data->seq_count;
 	smp_wmb(); /* Pairs with smp_rmb in vdso_read_retry */
 }

 static void vdso_write_end(struct vdso_data *vdata)
 {
 	smp_wmb(); /* Pairs with smp_rmb in vdso_read_begin */
 	++vdso_data->seq_count;
 }

 static bool tk_is_cntvct(const struct timekeeper *tk)
 {
 	if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
 		return false;

 	if (!tk->tkr_mono.clock->archdata.vdso_direct)
 		return false;

 	return true;
 }

 /**
  * update_vsyscall - update the vdso data page
  *
  * Increment the sequence counter, making it odd, indicating to
  * userspace that an update is in progress.  Update the fields used
  * for coarse clocks and, if the architected system timer is in use,
  * the fields used for high precision clocks.  Increment the sequence
  * counter again, making it even, indicating to userspace that the
  * update is finished.
  *
  * Userspace is expected to sample seq_count before reading any other
  * fields from the data page.  If seq_count is odd, userspace is
  * expected to wait until it becomes even.  After copying data from
  * the page, userspace must sample seq_count again; if it has changed
  * from its previous value, userspace must retry the whole sequence.
  *
  * Calls to update_vsyscall are serialized by the timekeeping core.
  */
 void update_vsyscall(struct timekeeper *tk)
 {
 	struct timespec64 *wtm = &tk->wall_to_monotonic;

 	if (!cntvct_ok) {
 		/* The entry points have been zeroed, so there is no
 		 * point in updating the data page.
 		 */
 		return;
 	}

 	vdso_write_begin(vdso_data);

 	vdso_data->tk_is_cntvct			= tk_is_cntvct(tk);
 	vdso_data->xtime_coarse_sec		= tk->xtime_sec;
 	vdso_data->xtime_coarse_nsec		= (u32)(tk->tkr_mono.xtime_nsec >>
 							tk->tkr_mono.shift);
 	vdso_data->wtm_clock_sec		= wtm->tv_sec;
 	vdso_data->wtm_clock_nsec		= wtm->tv_nsec;

 	if (vdso_data->tk_is_cntvct) {
 		vdso_data->cs_cycle_last	= tk->tkr_mono.cycle_last;
 		vdso_data->xtime_clock_sec	= tk->xtime_sec;
 		vdso_data->xtime_clock_snsec	= tk->tkr_mono.xtime_nsec;
 		vdso_data->cs_mult		= tk->tkr_mono.mult;
 		vdso_data->cs_shift		= tk->tkr_mono.shift;
 		vdso_data->cs_mask		= tk->tkr_mono.mask;
 	}

 	vdso_write_end(vdso_data);

 	flush_dcache_page(virt_to_page(vdso_data));
 }

 void update_vsyscall_tz(void)
 {
 	vdso_data->tz_minuteswest	= sys_tz.tz_minuteswest;
 	vdso_data->tz_dsttime		= sys_tz.tz_dsttime;
 	flush_dcache_page(virt_to_page(vdso_data));
 }
	/*
	* Adapted from arm64 version.
	*
	* Copyright (C) 2012 ARM Limited
	* Copyright (C) 2015 Mentor Graphics Corporation.
	*
	* This program is free software; you can redistribute it and/or modify
	* it under the terms of the GNU General Public License version 2 as
	* published by the Free Software Foundation.
	*
	* This program is distributed in the hope that it will be useful,
	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	* GNU General Public License for more details.
	*
	* You should have received a copy of the GNU General Public License
	* along with this program. If not, see <http://www.gnu.org/licenses/>.
	*/

	#include <linux/cache.h>
	#include <linux/elf.h>
	#include <linux/err.h>
	#include <linux/kernel.h>
	#include <linux/mm.h>
	#include <linux/of.h>
	#include <linux/printk.h>
	#include <linux/slab.h>
	#include <linux/timekeeper_internal.h>
	#include <linux/vmalloc.h>
	#include <asm/arch_timer.h>
	#include <asm/barrier.h>
	#include <asm/cacheflush.h>
	#include <asm/page.h>
	#include <asm/vdso.h>
	#include <asm/vdso_datapage.h>
	#include <clocksource/arm_arch_timer.h>

	#define MAX_SYMNAME 64

	static struct page **vdso_text_pagelist;

	/* Total number of pages needed for the data and text portions of the VDSO. */
	unsigned int vdso_total_pages __ro_after_init;

	/*
	* The VDSO data page.
	*/
	static union vdso_data_store vdso_data_store __page_aligned_data;
	static struct vdso_data *vdso_data = &vdso_data_store.data;

	static struct page *vdso_data_page __ro_after_init;
	static const struct vm_special_mapping vdso_data_mapping = {
	.name = "[vvar]",
	.pages = &vdso_data_page,
	};

	static int vdso_mremap(const struct vm_special_mapping *sm,
	struct vm_area_struct *new_vma)
	{
	unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
	unsigned long vdso_size;

	/* without VVAR page */
	vdso_size = (vdso_total_pages - 1) << PAGE_SHIFT;

	if (vdso_size != new_size)
	return -EINVAL;

	current->mm->context.vdso = new_vma->vm_start;

	return 0;
	}

	static struct vm_special_mapping vdso_text_mapping __ro_after_init = {
	.name = "[vdso]",
	.mremap = vdso_mremap,
	};

	struct elfinfo {
	Elf32_Ehdr hdr; / ptr to ELF */
	Elf32_Sym dynsym; / ptr to .dynsym section */
	unsigned long dynsymsize; /* size of .dynsym section */
	char dynstr; / ptr to .dynstr section */
	};

	/* Cached result of boot-time check for whether the arch timer exists,
	* and if so, whether the virtual counter is useable.
	*/
	static bool cntvct_ok __ro_after_init;

	static bool __init cntvct_functional(void)
	{
	struct device_node *np;
	bool ret = false;

	if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
	goto out;

	/* The arm_arch_timer core should export
	* arch_timer_use_virtual or similar so we don't have to do
	* this.
	*/
	np = of_find_compatible_node(NULL, NULL, "arm,armv7-timer");
	if (!np)
	goto out_put;

	if (of_property_read_bool(np, "arm,cpu-registers-not-fw-configured"))
	goto out_put;

	ret = true;

	out_put:
	of_node_put(np);
	out:
	return ret;
	}

	static void * __init find_section(Elf32_Ehdr ehdr, const char name,
	unsigned long *size)
	{
	Elf32_Shdr *sechdrs;
	unsigned int i;
	char *secnames;

	/* Grab section headers and strings so we can tell who is who */
	sechdrs = (void *)ehdr + ehdr->e_shoff;
	secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;

	/* Find the section they want */
	for (i = 1; i < ehdr->e_shnum; i++) {
	if (strcmp(secnames + sechdrs[i].sh_name, name) == 0) {
	if (size)
	*size = sechdrs[i].sh_size;
	return (void *)ehdr + sechdrs[i].sh_offset;
	}
	}

	if (size)
	*size = 0;
	return NULL;
	}

	static Elf32_Sym * __init find_symbol(struct elfinfo lib, const char symname)
	{
	unsigned int i;

	for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
	char name[MAX_SYMNAME], *c;

	if (lib->dynsym[i].st_name == 0)
	continue;
	strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
	MAX_SYMNAME);
	c = strchr(name, '@');
	if (c)
	*c = 0;
	if (strcmp(symname, name) == 0)
	return &lib->dynsym[i];
	}
	return NULL;
	}

	static void __init vdso_nullpatch_one(struct elfinfo lib, const char symname)
	{
	Elf32_Sym *sym;

	sym = find_symbol(lib, symname);
	if (!sym)
	return;

	sym->st_name = 0;
	}

	static void __init patch_vdso(void *ehdr)
	{
	struct elfinfo einfo;

	einfo = (struct elfinfo) {
	.hdr = ehdr,
	};

	einfo.dynsym = find_section(einfo.hdr, ".dynsym", &einfo.dynsymsize);
	einfo.dynstr = find_section(einfo.hdr, ".dynstr", NULL);

	/* If the virtual counter is absent or non-functional we don't
	* want programs to incur the slight additional overhead of
	* dispatching through the VDSO only to fall back to syscalls.
	*/
	if (!cntvct_ok) {
	vdso_nullpatch_one(&einfo, "__vdso_gettimeofday");
	vdso_nullpatch_one(&einfo, "__vdso_clock_gettime");
	}
	}

	static int __init vdso_init(void)
	{
	unsigned int text_pages;
	int i;

	if (memcmp(&vdso_start, "\177ELF", 4)) {
	pr_err("VDSO is not a valid ELF object!\n");
	return -ENOEXEC;
	}

	text_pages = (&vdso_end - &vdso_start) >> PAGE_SHIFT;
	pr_debug("vdso: %i text pages at base %p\n", text_pages, &vdso_start);

	/* Allocate the VDSO text pagelist */
	vdso_text_pagelist = kcalloc(text_pages, sizeof(struct page *),
	GFP_KERNEL);
	if (vdso_text_pagelist == NULL)
	return -ENOMEM;

	/* Grab the VDSO data page. */
	vdso_data_page = virt_to_page(vdso_data);

	/* Grab the VDSO text pages. */
	for (i = 0; i < text_pages; i++) {
	struct page *page;

	page = virt_to_page(&vdso_start + i * PAGE_SIZE);
	vdso_text_pagelist[i] = page;
	}

	vdso_text_mapping.pages = vdso_text_pagelist;

	vdso_total_pages = 1; /* for the data/vvar page */
	vdso_total_pages += text_pages;

	cntvct_ok = cntvct_functional();

	patch_vdso(&vdso_start);

	return 0;
	}
	arch_initcall(vdso_init);

	static int install_vvar(struct mm_struct *mm, unsigned long addr)
	{
	struct vm_area_struct *vma;

	vma = _install_special_mapping(mm, addr, PAGE_SIZE,
	VM_READ \| VM_MAYREAD,
	&vdso_data_mapping);

	return PTR_ERR_OR_ZERO(vma);
	}

	/* assumes mmap_sem is write-locked */
	void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
	{
	struct vm_area_struct *vma;
	unsigned long len;

	mm->context.vdso = 0;

	if (vdso_text_pagelist == NULL)
	return;

	if (install_vvar(mm, addr))
	return;

	/* Account for vvar page. */
	addr += PAGE_SIZE;
	len = (vdso_total_pages - 1) << PAGE_SHIFT;

	vma = _install_special_mapping(mm, addr, len,
	VM_READ \| VM_EXEC \| VM_MAYREAD \| VM_MAYWRITE \| VM_MAYEXEC,
	&vdso_text_mapping);

	if (!IS_ERR(vma))
	mm->context.vdso = addr;
	}

	static void vdso_write_begin(struct vdso_data *vdata)
	{
	++vdso_data->seq_count;
	smp_wmb(); /* Pairs with smp_rmb in vdso_read_retry */
	}

	static void vdso_write_end(struct vdso_data *vdata)
	{
	smp_wmb(); /* Pairs with smp_rmb in vdso_read_begin */
	++vdso_data->seq_count;
	}

	static bool tk_is_cntvct(const struct timekeeper *tk)
	{
	if (!IS_ENABLED(CONFIG_ARM_ARCH_TIMER))
	return false;

	if (!tk->tkr_mono.clock->archdata.vdso_direct)
	return false;

	return true;
	}

	/**
	* update_vsyscall - update the vdso data page
	*
	* Increment the sequence counter, making it odd, indicating to
	* userspace that an update is in progress. Update the fields used
	* for coarse clocks and, if the architected system timer is in use,
	* the fields used for high precision clocks. Increment the sequence
	* counter again, making it even, indicating to userspace that the
	* update is finished.
	*
	* Userspace is expected to sample seq_count before reading any other
	* fields from the data page. If seq_count is odd, userspace is
	* expected to wait until it becomes even. After copying data from
	* the page, userspace must sample seq_count again; if it has changed
	* from its previous value, userspace must retry the whole sequence.
	*
	* Calls to update_vsyscall are serialized by the timekeeping core.
	*/
	void update_vsyscall(struct timekeeper *tk)
	{
	struct timespec64 *wtm = &tk->wall_to_monotonic;

	if (!cntvct_ok) {
	/* The entry points have been zeroed, so there is no
	* point in updating the data page.
	*/
	return;
	}

	vdso_write_begin(vdso_data);

	vdso_data->tk_is_cntvct = tk_is_cntvct(tk);
	vdso_data->xtime_coarse_sec = tk->xtime_sec;
	vdso_data->xtime_coarse_nsec = (u32)(tk->tkr_mono.xtime_nsec >>
	tk->tkr_mono.shift);
	vdso_data->wtm_clock_sec = wtm->tv_sec;
	vdso_data->wtm_clock_nsec = wtm->tv_nsec;

	if (vdso_data->tk_is_cntvct) {
	vdso_data->cs_cycle_last = tk->tkr_mono.cycle_last;
	vdso_data->xtime_clock_sec = tk->xtime_sec;
	vdso_data->xtime_clock_snsec = tk->tkr_mono.xtime_nsec;
	vdso_data->cs_mult = tk->tkr_mono.mult;
	vdso_data->cs_shift = tk->tkr_mono.shift;
	vdso_data->cs_mask = tk->tkr_mono.mask;
	}

	vdso_write_end(vdso_data);

	flush_dcache_page(virt_to_page(vdso_data));
	}

	void update_vsyscall_tz(void)
	{
	vdso_data->tz_minuteswest = sys_tz.tz_minuteswest;
	vdso_data->tz_dsttime = sys_tz.tz_dsttime;
	flush_dcache_page(virt_to_page(vdso_data));
	}