diff mbox series

[03/17] vdso: Add generic time data storage

Message ID 20241216-vdso-store-rng-v1-3-f7aed1bdb3b2@linutronix.de (mailing list archive)
State New
Headers show
Series vDSO: Introduce generic data storage | expand

Commit Message

Thomas Weißschuh Dec. 16, 2024, 2:09 p.m. UTC 
Historically each architecture defined their own way to store the vDSO
data page. Add a generic mechanism to provide storage for that page.

Furthermore this generic storage will be extended to also provide
uniform storage for *non*-time-related data, like the random state or
architecture-specific data. These will have their own pages and data
structures, so rename 'vdso_data' into 'vdso_time_data' to make that
split clear from the name.

Also introduce a new consistent naming scheme for the symbols related to
the vDSO, which makes it clear if the symbol is accessible from
userspace or kernel space and the type of data behind the symbol.

The generic fault handler contains an optimization to prefault the vvar
page when the timens page is accessed. This was lifted from s390 and x86.

Co-developed-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Nam Cao <namcao@linutronix.de>
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
---
 MAINTAINERS                    |  1 +
 include/linux/time_namespace.h |  1 +
 include/linux/vdso_datastore.h | 10 +++++
 include/vdso/datapage.h        | 69 +++++++++++++++++++++++++----
 lib/Kconfig                    |  1 +
 lib/Makefile                   |  2 +
 lib/vdso_kernel/Kconfig        |  7 +++
 lib/vdso_kernel/Makefile       |  3 ++
 lib/vdso_kernel/datastore.c    | 99 ++++++++++++++++++++++++++++++++++++++++++
 9 files changed, 185 insertions(+), 8 deletions(-)
diff mbox series

Patch

diff --git a/MAINTAINERS b/MAINTAINERS
index 1e930c7a58b13d8bbe6bf133ba7b36aa24c2b5e0..9d947e1e90ff3c6060e56f3b7eaa28cd60d6191c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9677,6 +9677,7 @@  F:	include/asm-generic/vdso/vsyscall.h
 F:	include/vdso/
 F:	kernel/time/vsyscall.c
 F:	lib/vdso/
+F:	lib/vdso_kernel/
 
 GENWQE (IBM Generic Workqueue Card)
 M:	Frank Haverkamp <haver@linux.ibm.com>
diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index 876e31b4461d0ee01fe2bd3d136acdea2611789f..4b81db223f5450218dfaf553b24195be9ba97c08 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -8,6 +8,7 @@ 
 #include <linux/ns_common.h>
 #include <linux/err.h>
 #include <linux/time64.h>
+#include <vdso/datapage.h>
 
 struct user_namespace;
 extern struct user_namespace init_user_ns;
diff --git a/include/linux/vdso_datastore.h b/include/linux/vdso_datastore.h
new file mode 100644
index 0000000000000000000000000000000000000000..a91fa24b06e09321fdff8c2c7bdfbc1b206db574
--- /dev/null
+++ b/include/linux/vdso_datastore.h
@@ -0,0 +1,10 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_VDSO_DATASTORE_H
+#define _LINUX_VDSO_DATASTORE_H
+
+#include <linux/mm_types.h>
+
+extern const struct vm_special_mapping vdso_vvar_mapping;
+struct vm_area_struct *vdso_install_vvar_mapping(struct mm_struct *mm, unsigned long addr);
+
+#endif /* _LINUX_VDSO_DATASTORE_H */
diff --git a/include/vdso/datapage.h b/include/vdso/datapage.h
index d967baa0cd0c65784e38dc4fcd7b9e8273923947..69af424413db1f265607d0f1bdbf88550548c5ba 100644
--- a/include/vdso/datapage.h
+++ b/include/vdso/datapage.h
@@ -45,11 +45,11 @@  struct arch_vdso_time_data {};
  *
  * There is one vdso_timestamp object in vvar for each vDSO-accelerated
  * clock_id. For high-resolution clocks, this encodes the time
- * corresponding to vdso_data.cycle_last. For coarse clocks this encodes
+ * corresponding to vdso_time_data.cycle_last. For coarse clocks this encodes
  * the actual time.
  *
  * To be noticed that for highres clocks nsec is left-shifted by
- * vdso_data.cs[x].shift.
+ * vdso_time_data[x].shift.
  */
 struct vdso_timestamp {
 	u64	sec;
@@ -57,7 +57,7 @@  struct vdso_timestamp {
 };
 
 /**
- * struct vdso_data - vdso datapage representation
+ * struct vdso_time_data - vdso datapage representation
  * @seq:		timebase sequence counter
  * @clock_mode:		clock mode
  * @cycle_last:		timebase at clocksource init
@@ -74,7 +74,7 @@  struct vdso_timestamp {
  * @arch_data:		architecture specific data (optional, defaults
  *			to an empty struct)
  *
- * vdso_data will be accessed by 64 bit and compat code at the same time
+ * vdso_time_data will be accessed by 64 bit and compat code at the same time
  * so we should be careful before modifying this structure.
  *
  * The ordering of the struct members is optimized to have fast access to the
@@ -92,7 +92,7 @@  struct vdso_timestamp {
  * For clocks which are not affected by time namespace adjustment the
  * offset must be zero.
  */
-struct vdso_data {
+struct vdso_time_data {
 	u32			seq;
 
 	s32			clock_mode;
@@ -117,6 +117,8 @@  struct vdso_data {
 	struct arch_vdso_time_data arch_data;
 };
 
+#define vdso_data vdso_time_data
+
 /**
  * struct vdso_rng_data - vdso RNG state information
  * @generation:	counter representing the number of RNG reseeds
@@ -136,18 +138,55 @@  struct vdso_rng_data {
  * With the hidden visibility, the compiler simply generates a PC-relative
  * relocation, and this is what we need.
  */
-extern struct vdso_data _vdso_data[CS_BASES] __attribute__((visibility("hidden")));
-extern struct vdso_data _timens_data[CS_BASES] __attribute__((visibility("hidden")));
+#ifndef CONFIG_GENERIC_VDSO_DATA_STORE
+extern struct vdso_time_data _vdso_data[CS_BASES] __attribute__((visibility("hidden")));
+extern struct vdso_time_data _timens_data[CS_BASES] __attribute__((visibility("hidden")));
 extern struct vdso_rng_data _vdso_rng_data __attribute__((visibility("hidden")));
+#else
+extern const struct vdso_time_data vdso_u_time_data[CS_BASES] __attribute__((visibility("hidden")));
+extern const struct vdso_time_data vdso_u_timens_data[CS_BASES] __attribute__((visibility("hidden")));
+
+extern struct vdso_time_data *vdso_k_time_data;
+#endif
 
 /**
  * union vdso_data_store - Generic vDSO data page
  */
 union vdso_data_store {
-	struct vdso_data	data[CS_BASES];
+	struct vdso_time_data	data[CS_BASES];
 	u8			page[1U << CONFIG_PAGE_SHIFT];
 };
 
+#ifdef CONFIG_GENERIC_VDSO_DATA_STORE
+
+enum vdso_pages {
+	VDSO_TIME_PAGE_OFFSET,
+	VDSO_TIMENS_PAGE_OFFSET,
+	VDSO_NR_PAGES
+};
+
+static __always_inline struct vdso_time_data *__arch_get_vdso_k_time_data(void)
+{
+	return vdso_k_time_data;
+}
+#define __arch_get_k_vdso_data __arch_get_vdso_k_time_data
+
+static __always_inline const struct vdso_time_data *__arch_get_vdso_u_time_data(void)
+{
+	return vdso_u_time_data;
+}
+#define __arch_get_vdso_data __arch_get_vdso_u_time_data
+
+#ifdef CONFIG_TIME_NS
+static __always_inline const struct vdso_time_data *__arch_get_vdso_u_timens_data(void)
+{
+	return vdso_u_timens_data;
+}
+#define __arch_get_timens_vdso_data(vd) __arch_get_vdso_u_timens_data()
+#endif /* CONFIG_TIME_NS */
+
+#endif /* CONFIG_GENERIC_VDSO_DATA_STORE */
+
 /*
  * The generic vDSO implementation requires that gettimeofday.h
  * provides:
@@ -164,6 +203,20 @@  union vdso_data_store {
 #include <asm/vdso/gettimeofday.h>
 #endif /* ENABLE_COMPAT_VDSO */
 
+#else /* !__ASSEMBLY__ */
+
+#ifdef CONFIG_TIME_NS
+#define __vdso_u_timens_data	PROVIDE(vdso_u_timens_data = vdso_u_data + PAGE_SIZE);
+#else
+#define __vdso_u_timens_data
+#endif
+
+#define VDSO_VVAR_SYMS						\
+	PROVIDE(vdso_u_data = . - __VDSO_PAGES * PAGE_SIZE);	\
+	PROVIDE(vdso_u_time_data = vdso_u_data);		\
+	__vdso_u_timens_data					\
+
+
 #endif /* !__ASSEMBLY__ */
 
 #endif /* __VDSO_DATAPAGE_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index 5a318f753b2f44cb0a7905cc0092e81c133bc112..7d59b2c10ce5ffab03378ead254d9f9017a4482f 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -659,6 +659,7 @@  config UCS2_STRING
 # generic vdso
 #
 source "lib/vdso/Kconfig"
+source "lib/vdso_kernel/Kconfig"
 
 source "lib/fonts/Kconfig"
 
diff --git a/lib/Makefile b/lib/Makefile
index a8155c972f02856fcc61ee949ddda436cfe211ff..aeedeea86b26cee50d7ced18f9b77b3c51201930 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -401,3 +401,5 @@  obj-$(CONFIG_GENERIC_LIB_DEVMEM_IS_ALLOWED) += devmem_is_allowed.o
 obj-$(CONFIG_FIRMWARE_TABLE) += fw_table.o
 
 subdir-$(CONFIG_FORTIFY_SOURCE) += test_fortify
+
+obj-y += vdso_kernel/
diff --git a/lib/vdso_kernel/Kconfig b/lib/vdso_kernel/Kconfig
new file mode 100644
index 0000000000000000000000000000000000000000..0c7ade9b3ece67c0c0ca892544b9e29e53c860c4
--- /dev/null
+++ b/lib/vdso_kernel/Kconfig
@@ -0,0 +1,7 @@ 
+# SPDX-License-Identifier: GPL-2.0
+
+config GENERIC_VDSO_DATA_STORE
+	bool
+	depends on HAVE_GENERIC_VDSO
+	help
+	  Selected by architectures that use the generic vDSO data store.
diff --git a/lib/vdso_kernel/Makefile b/lib/vdso_kernel/Makefile
new file mode 100644
index 0000000000000000000000000000000000000000..4826e49f9edbdb48506b50957584ed89bde5f37f
--- /dev/null
+++ b/lib/vdso_kernel/Makefile
@@ -0,0 +1,3 @@ 
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_GENERIC_VDSO_DATA_STORE) += datastore.o
diff --git a/lib/vdso_kernel/datastore.c b/lib/vdso_kernel/datastore.c
new file mode 100644
index 0000000000000000000000000000000000000000..c9cd269b1ed1b6cdd5fdf9fe929d0b778314b962
--- /dev/null
+++ b/lib/vdso_kernel/datastore.c
@@ -0,0 +1,99 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/linkage.h>
+#include <linux/mmap_lock.h>
+#include <linux/mm.h>
+#include <linux/time_namespace.h>
+#include <linux/types.h>
+#include <linux/vdso_datastore.h>
+#include <vdso/datapage.h>
+
+/*
+ * The vDSO data page.
+ */
+static union vdso_data_store vdso_time_data_store __page_aligned_data;
+struct vdso_time_data *vdso_k_time_data = vdso_time_data_store.data;
+static_assert(sizeof(vdso_time_data_store) == PAGE_SIZE);
+
+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 addr, pfn;
+	vm_fault_t err;
+
+	switch (vmf->pgoff) {
+	case VDSO_TIME_PAGE_OFFSET:
+		pfn = __phys_to_pfn(__pa_symbol(vdso_k_time_data));
+		if (timens_page) {
+			/*
+			 * Fault in VVAR page too, since it will be accessed
+			 * to get clock data anyway.
+			 */
+			addr = vmf->address + VDSO_TIMENS_PAGE_OFFSET * PAGE_SIZE;
+			err = vmf_insert_pfn(vma, addr, pfn);
+			if (unlikely(err & VM_FAULT_ERROR))
+				return err;
+			pfn = page_to_pfn(timens_page);
+		}
+		break;
+	case VDSO_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 (!IS_ENABLED(CONFIG_TIME_NS) || !timens_page)
+			return VM_FAULT_SIGBUS;
+		pfn = __phys_to_pfn(__pa_symbol(vdso_k_time_data));
+		break;
+	default:
+		return VM_FAULT_SIGBUS;
+	}
+
+	return vmf_insert_pfn(vma, vmf->address, pfn);
+}
+
+const struct vm_special_mapping vdso_vvar_mapping = {
+	.name	= "[vvar]",
+	.fault	= vvar_fault,
+};
+
+struct vm_area_struct *vdso_install_vvar_mapping(struct mm_struct *mm, unsigned long addr)
+{
+	return _install_special_mapping(mm, addr, VDSO_NR_PAGES * PAGE_SIZE,
+					VM_READ | VM_MAYREAD | VM_IO | VM_DONTDUMP | VM_PFNMAP,
+					&vdso_vvar_mapping);
+}
+
+#ifdef CONFIG_TIME_NS
+/*
+ * The vvar page layout depends on whether a task belongs to the root or
+ * non-root time namespace. Whenever a task changes its namespace, the VVAR
+ * page tables are cleared and then they will be re-faulted with a
+ * corresponding layout.
+ * See also the comment near timens_setup_vdso_data() for details.
+ */
+int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
+{
+	struct mm_struct *mm = task->mm;
+	struct vm_area_struct *vma;
+	VMA_ITERATOR(vmi, mm, 0);
+
+	mmap_read_lock(mm);
+	for_each_vma(vmi, vma) {
+		if (vma_is_special_mapping(vma, &vdso_vvar_mapping))
+			zap_vma_pages(vma);
+	}
+	mmap_read_unlock(mm);
+
+	return 0;
+}
+#endif
+
+struct vdso_time_data *arch_get_vdso_data(void *vvar_page)
+{
+	return (struct vdso_time_data *)vvar_page;
+}