[PATCH v7 8/9] ARM: vdso initialization, mapping, and synchronization
Nathan Lynch
nathan_lynch at mentor.com
Sun Jun 22 20:11:57 PDT 2014
Initialize the vdso page list at boot, install the vdso mapping at
exec time, and update the data page during timer ticks. This code is
not built if CONFIG_VDSO is not enabled.
Account for the vdso length when randomizing the offset from the
stack. The vdso is placed immediately following the sigpage with a
separate install_special_mapping call in arm_install_vdso.
Signed-off-by: Nathan Lynch <nathan_lynch at mentor.com>
---
arch/arm/kernel/process.c | 13 +++-
arch/arm/kernel/vdso.c | 168 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 179 insertions(+), 2 deletions(-)
create mode 100644 arch/arm/kernel/vdso.c
diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 40445fb71ac9..39b0d68aa068 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -520,6 +520,7 @@ extern struct page *get_signal_page(void);
int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
{
struct mm_struct *mm = current->mm;
+ unsigned long npages;
unsigned long addr;
unsigned long hint;
int ret;
@@ -529,9 +530,11 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
if (!signal_page)
return -ENOMEM;
+ npages = (vdso_mapping_len >> PAGE_SHIFT) + 1;
+
down_write(&mm->mmap_sem);
- hint = vdso_addr(mm, 1);
- addr = get_unmapped_area(NULL, hint, PAGE_SIZE, 0, 0);
+ hint = vdso_addr(mm, npages);
+ addr = get_unmapped_area(NULL, hint, npages, 0, 0);
if (IS_ERR_VALUE(addr)) {
ret = addr;
goto up_fail;
@@ -544,6 +547,12 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
if (ret == 0)
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;
diff --git a/arch/arm/kernel/vdso.c b/arch/arm/kernel/vdso.c
new file mode 100644
index 000000000000..0cfd25f09adf
--- /dev/null
+++ b/arch/arm/kernel/vdso.c
@@ -0,0 +1,168 @@
+/*
+ * Adapted from arm64 version.
+ *
+ * Copyright (C) 2012 ARM Limited
+ *
+ * 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/err.h>
+#include <linux/kernel.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/timekeeper_internal.h>
+#include <linux/vmalloc.h>
+
+#include <asm/barrier.h>
+#include <asm/cacheflush.h>
+#include <asm/page.h>
+#include <asm/vdso.h>
+#include <asm/vdso_datapage.h>
+
+static struct page **vdso_pagelist;
+
+unsigned long vdso_mapping_len __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 int __init vdso_init(void)
+{
+ unsigned long vdso_pages;
+ int i;
+
+ if (memcmp(&vdso_start, "\177ELF", 4)) {
+ pr_err("vDSO is not a valid ELF object!\n");
+ return -ENOEXEC;
+ }
+
+ vdso_pages = (&vdso_end - &vdso_start) >> PAGE_SHIFT;
+ pr_debug("vdso: %ld code pages at base %p\n", vdso_pages, &vdso_start);
+
+ /* Allocate the vDSO pagelist, plus a page for the data. */
+ vdso_pagelist = kcalloc(vdso_pages + 1, sizeof(struct page *),
+ GFP_KERNEL);
+ if (vdso_pagelist == NULL)
+ return -ENOMEM;
+
+ /* Grab the vDSO data page. */
+ vdso_pagelist[0] = virt_to_page(vdso_data);
+
+ /* Grab the vDSO code pages. */
+ for (i = 0; i < vdso_pages; i++)
+ vdso_pagelist[i + 1] = virt_to_page(&vdso_start + i * PAGE_SIZE);
+
+ /* Precompute the mapping size */
+ vdso_mapping_len = (vdso_pages + 1) << PAGE_SHIFT;
+
+ return 0;
+}
+arch_initcall(vdso_init);
+
+/* assumes mmap_sem is write-locked */
+void arm_install_vdso(struct mm_struct *mm, unsigned long addr)
+{
+ int ret;
+
+ mm->context.vdso = ~0UL;
+
+ if (vdso_pagelist == NULL)
+ return;
+
+ /*
+ * Put vDSO base into mm struct before calling
+ * install_special_mapping so the perf counter mmap tracking
+ * code will recognise it as a vDSO.
+ */
+ mm->context.vdso = addr;
+
+ ret = install_special_mapping(mm, addr, vdso_mapping_len,
+ VM_READ|VM_EXEC|
+ VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
+ vdso_pagelist);
+ if (ret) {
+ pr_notice_once("%s: install_special_mapping failed (%d)\n",
+ __func__, ret);
+ mm->context.vdso = ~0UL;
+ return;
+ }
+}
+
+static void vdso_write_begin(struct vdso_data *vdata)
+{
+ ++vdso_data->seq_count;
+ smp_wmb();
+}
+
+static void vdso_write_end(struct vdso_data *vdata)
+{
+ smp_wmb();
+ ++vdso_data->seq_count;
+}
+
+/**
+ * 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 timespec *wtm = &tk->wall_to_monotonic;
+ bool use_syscall = strcmp(tk->clock->name, "arch_sys_counter");
+
+ vdso_write_begin(vdso_data);
+
+ xtime_coarse = __current_kernel_time();
+ vdso_data->use_syscall = use_syscall;
+ 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 (!use_syscall) {
+ vdso_data->cs_cycle_last = tk->cycle_last;
+ vdso_data->xtime_clock_sec = tk->xtime_sec;
+ vdso_data->xtime_clock_snsec = tk->xtime_nsec;
+ vdso_data->cs_mult = tk->mult;
+ vdso_data->cs_shift = tk->shift;
+ vdso_data->cs_mask = tk->clock->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));
+}
--
1.9.3
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