ARM: 8331/1: VDSO initialization, mapping, and synchronization

#include <asm/system_misc.h>

#include <asm/mach/time.h>

#include <asm/tls.h>

#include <asm/vdso.h>

#ifdef CONFIG_CC_STACKPROTECTOR

#include <linux/stackprotector.h>

}

/* If possible, provide a placement hint at a random offset from the

 * stack for the signal page.

 * stack for the sigpage and vdso pages.

 */

static unsigned long sigpage_addr(const struct mm_struct *mm,

				  unsigned int npages)

{

	struct mm_struct *mm = current->mm;

	struct vm_area_struct *vma;

	unsigned long npages;

	unsigned long addr;

	unsigned long hint;

	int ret = 0;

	if (!signal_page)

		return -ENOMEM;

	npages = 1; /* for sigpage */

	npages += vdso_total_pages;

	down_write(&mm->mmap_sem);

	hint = sigpage_addr(mm, 1);

	addr = get_unmapped_area(NULL, hint, PAGE_SIZE, 0, 0);

	hint = sigpage_addr(mm, npages);

	addr = get_unmapped_area(NULL, hint, npages << PAGE_SHIFT, 0, 0);

	if (IS_ERR_VALUE(addr)) {

		ret = addr;

		goto up_fail;

	mm->context.sigpage = addr;

	/* Unlike the sigpage, failure to install the vdso is unlikely

	 * to be fatal to the process, so no error check needed

	 * here.

	 */

	arm_install_vdso(mm, addr + PAGE_SIZE);

 up_fail:

	up_write(&mm->mmap_sem);

	return ret;

/*

 * 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/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 __read_mostly;

/*

 * 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;

static struct vm_special_mapping vdso_data_mapping = {

	.name = "[vvar]",

	.pages = &vdso_data_page,

};

static struct vm_special_mapping vdso_text_mapping = {

	.name = "[vdso]",

};

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 __read_mostly;

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 IS_ERR(vma) ? PTR_ERR(vma) : 0;

}

/* 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 (strcmp(tk->tkr.clock->name, "arch_sys_counter") != 0)

		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 timespec xtime_coarse;

	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);

	xtime_coarse = __current_kernel_time();

	vdso_data->tk_is_cntvct			= tk_is_cntvct(tk);

	vdso_data->xtime_coarse_sec		= xtime_coarse.tv_sec;

	vdso_data->xtime_coarse_nsec		= xtime_coarse.tv_nsec;

	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.cycle_last;

		vdso_data->xtime_clock_sec	= tk->xtime_sec;

		vdso_data->xtime_clock_snsec	= tk->tkr.xtime_nsec;

		vdso_data->cs_mult		= tk->tkr.mult;

		vdso_data->cs_shift		= tk->tkr.shift;

		vdso_data->cs_mask		= tk->tkr.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));

}