linux/arch/arm/kernel/vdso.c
Nathan Lynch 09edea4f8f ARM: 8410/1: VDSO: fix coarse clock monotonicity regression
Since 906c55579a ("timekeeping: Copy the shadow-timekeeper over the
real timekeeper last") it has become possible on ARM to:

- Obtain a CLOCK_MONOTONIC_COARSE or CLOCK_REALTIME_COARSE timestamp
  via syscall.
- Subsequently obtain a timestamp for the same clock ID via VDSO which
  predates the first timestamp (by one jiffy).

This is because ARM's update_vsyscall is deriving the coarse time
using the __current_kernel_time interface, when it should really be
using the timekeeper object provided to it by the timekeeping core.
It happened to work before only because __current_kernel_time would
access the same timekeeper object which had been passed to
update_vsyscall.  This is no longer the case.

Cc: stable@vger.kernel.org
Fixes: 906c55579a ("timekeeping: Copy the shadow-timekeeper over the real timekeeper last")
Signed-off-by: Nathan Lynch <nathan_lynch@mentor.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
2015-08-11 13:42:44 +01:00

337 lines
8.4 KiB
C

/*
* 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_mono.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 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));
}