[PATCH RESEND v1 4/4] powerpc/vdso: Add support for time namespaces

Christophe Leroy
2021-03-31T16:49:37Z

This patch adds the necessary glue to provide time namespaces.

Things are mainly copied from ARM64.

__arch_get_timens_vdso_data() calculates timens vdso data position
based on the vdso data position, knowing it is the next page in vvar.
This avoids having to redo the mflr/bcl/mflr/mtlr dance to locate
the page relative to running code position.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
arch/powerpc/Kconfig | 3 +-
arch/powerpc/include/asm/vdso/gettimeofday.h | 10 ++
arch/powerpc/include/asm/vdso_datapage.h | 2 -
arch/powerpc/kernel/vdso.c | 116 ++++++++++++++++---
arch/powerpc/kernel/vdso32/vdso32.lds.S | 2 +-
arch/powerpc/kernel/vdso64/vdso64.lds.S | 2 +-
6 files changed, 114 insertions(+), 21 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index c1344c05226c..71daff5f15d5 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -172,6 +172,7 @@ config PPC
select GENERIC_CPU_AUTOPROBE
select GENERIC_CPU_VULNERABILITIES if PPC_BARRIER_NOSPEC
select GENERIC_EARLY_IOREMAP
+ select GENERIC_GETTIMEOFDAY
select GENERIC_IRQ_SHOW
select GENERIC_IRQ_SHOW_LEVEL
select GENERIC_PCI_IOMAP if PCI
@@ -179,7 +180,7 @@ config PPC
select GENERIC_STRNCPY_FROM_USER
select GENERIC_STRNLEN_USER
select GENERIC_TIME_VSYSCALL
- select GENERIC_GETTIMEOFDAY
+ select GENERIC_VDSO_TIME_NS
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_HUGE_VMAP if PPC_BOOK3S_64 && PPC_RADIX_MMU
select HAVE_ARCH_JUMP_LABEL
diff --git a/arch/powerpc/include/asm/vdso/gettimeofday.h b/arch/powerpc/include/asm/vdso/gettimeofday.h
index d453e725c79f..e448df1dd071 100644
--- a/arch/powerpc/include/asm/vdso/gettimeofday.h
+++ b/arch/powerpc/include/asm/vdso/gettimeofday.h
@@ -2,6 +2,8 @@
#ifndef _ASM_POWERPC_VDSO_GETTIMEOFDAY_H
#define _ASM_POWERPC_VDSO_GETTIMEOFDAY_H

+#include <asm/page.h>
+
#ifdef __ASSEMBLY__

#include <asm/ppc_asm.h>
@@ -153,6 +155,14 @@ static __always_inline u64 __arch_get_hw_counter(s32 clock_mode,

const struct vdso_data *__arch_get_vdso_data(void);

+#ifdef CONFIG_TIME_NS
+static __always_inline
+const struct vdso_data *__arch_get_timens_vdso_data(const struct vdso_data *vd)
+{
+ return (void *)vd + PAGE_SIZE;
+}
+#endif
+
static inline bool vdso_clocksource_ok(const struct vdso_data *vd)
{
return true;
diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
index 3f958ecf2beb..a585c8e538ff 100644
--- a/arch/powerpc/include/asm/vdso_datapage.h
+++ b/arch/powerpc/include/asm/vdso_datapage.h
@@ -107,9 +107,7 @@ extern struct vdso_arch_data *vdso_data;
bcl 20, 31, .+4
999:
mflr \ptr
-#if CONFIG_PPC_PAGE_SHIFT > 14
addis \ptr, \ptr, (_vdso_datapage - 999b)@ha
-#endif
addi \ptr, \ptr, (_vdso_datapage - 999b)@l
.endm

diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index b14907209822..717f2c9a7573 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -18,6 +18,7 @@
#include <linux/security.h>
#include <linux/memblock.h>
#include <linux/syscalls.h>
+#include <linux/time_namespace.h>
#include <vdso/datapage.h>

#include <asm/syscall.h>
@@ -50,6 +51,12 @@ static union {
} vdso_data_store __page_aligned_data;
struct vdso_arch_data *vdso_data = &vdso_data_store.data;

+enum vvar_pages {
+ VVAR_DATA_PAGE_OFFSET,
+ VVAR_TIMENS_PAGE_OFFSET,
+ VVAR_NR_PAGES,
+};
+
static int vdso_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma,
unsigned long text_size)
{
@@ -73,8 +80,12 @@ static int vdso64_mremap(const struct vm_special_mapping *sm, struct vm_area_str
return vdso_mremap(sm, new_vma, &vdso64_end - &vdso64_start);
}

+static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
+ struct vm_area_struct *vma, struct vm_fault *vmf);
+
static struct vm_special_mapping vvar_spec __ro_after_init = {
.name = "[vvar]",
+ .fault = vvar_fault,
};

static struct vm_special_mapping vdso32_spec __ro_after_init = {
@@ -87,6 +98,94 @@ static struct vm_special_mapping vdso64_spec __ro_after_init = {
.mremap = vdso64_mremap,
};

+#ifdef CONFIG_TIME_NS
+struct vdso_data *arch_get_vdso_data(void *vvar_page)
+{
+ return ((struct vdso_arch_data *)vvar_page)->data;
+}
+
+/*
+ * The vvar mapping contains data for a specific time namespace, so when a task
+ * changes namespace we must unmap its vvar data for the old namespace.
+ * Subsequent faults will map in data for the new namespace.
+ *
+ * For more details see timens_setup_vdso_data().
+ */
+int vdso_join_timens(struct task_struct *task, struct time_namespace *ns)
+{
+ struct mm_struct *mm = task->mm;
+ struct vm_area_struct *vma;
+
+ mmap_read_lock(mm);
+
+ for (vma = mm->mmap; vma; vma = vma->vm_next) {
+ unsigned long size = vma->vm_end - vma->vm_start;
+
+ if (vma_is_special_mapping(vma, &vvar_spec))
+ zap_page_range(vma, vma->vm_start, size);
+ }
+
+ mmap_read_unlock(mm);
+ return 0;
+}
+
+static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
+{
+ if (likely(vma->vm_mm == current->mm))
+ return current->nsproxy->time_ns->vvar_page;
+
+ /*
+ * VM_PFNMAP | VM_IO protect .fault() handler from being called
+ * through interfaces like /proc/$pid/mem or
+ * process_vm_{readv,writev}() as long as there's no .access()
+ * in special_mapping_vmops.
+ * For more details check_vma_flags() and __access_remote_vm()
+ */
+ WARN(1, "vvar_page accessed remotely");
+
+ return NULL;
+}
+#else
+static struct page *find_timens_vvar_page(struct vm_area_struct *vma)
+{
+ return NULL;
+}
+#endif
+
+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 pfn;
+
+ switch (vmf->pgoff) {
+ case VVAR_DATA_PAGE_OFFSET:
+ if (timens_page)
+ pfn = page_to_pfn(timens_page);
+ else
+ pfn = virt_to_pfn(vdso_data);
+ break;
+#ifdef CONFIG_TIME_NS
+ case VVAR_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 (!timens_page)
+ return VM_FAULT_SIGBUS;
+ pfn = virt_to_pfn(vdso_data);
+ break;
+#endif /* CONFIG_TIME_NS */
+ default:
+ return VM_FAULT_SIGBUS;
+ }
+
+ return vmf_insert_pfn(vma, vmf->address, pfn);
+}
+
/*
* This is called from binfmt_elf, we create the special vma for the
* vDSO and insert it into the mm struct tree
@@ -95,7 +194,7 @@ static int __arch_setup_additional_pages(struct linux_binprm *bprm, int uses_int
{
unsigned long vdso_size, vdso_base, mappings_size;
struct vm_special_mapping *vdso_spec;
- unsigned long vvar_size = PAGE_SIZE;
+ unsigned long vvar_size = VVAR_NR_PAGES * PAGE_SIZE;
struct mm_struct *mm = current->mm;
struct vm_area_struct *vma;

@@ -266,19 +365,6 @@ static struct page ** __init vdso_setup_pages(void *start, void *end)
return pagelist;
}

-static struct page ** __init vvar_setup_pages(void)
-{
- struct page **pagelist;
-
- /* .pages is NULL-terminated */
- pagelist = kcalloc(2, sizeof(struct page *), GFP_KERNEL);
- if (!pagelist)
- panic("%s: Cannot allocate page list for VVAR", __func__);
-
- pagelist[0] = virt_to_page(vdso_data);
- return pagelist;
-}
-
static int __init vdso_init(void)
{
#ifdef CONFIG_PPC64
@@ -317,8 +403,6 @@ static int __init vdso_init(void)
if (IS_ENABLED(CONFIG_PPC64))
vdso64_spec.pages = vdso_setup_pages(&vdso64_start, &vdso64_end);

- vvar_spec.pages = vvar_setup_pages();
-
smp_wmb();

return 0;
diff --git a/arch/powerpc/kernel/vdso32/vdso32.lds.S b/arch/powerpc/kernel/vdso32/vdso32.lds.S
index a4b806b0d618..58e0099f70f4 100644
--- a/arch/powerpc/kernel/vdso32/vdso32.lds.S
+++ b/arch/powerpc/kernel/vdso32/vdso32.lds.S
@@ -17,7 +17,7 @@ ENTRY(_start)

SECTIONS
{
- PROVIDE(_vdso_datapage = . - PAGE_SIZE);
+ PROVIDE(_vdso_datapage = . - 2 * PAGE_SIZE);
. = SIZEOF_HEADERS;

.hash : { *(.hash) } :text
diff --git a/arch/powerpc/kernel/vdso64/vdso64.lds.S b/arch/powerpc/kernel/vdso64/vdso64.lds.S
index 2f3c359cacd3..0288cad428b0 100644
--- a/arch/powerpc/kernel/vdso64/vdso64.lds.S
+++ b/arch/powerpc/kernel/vdso64/vdso64.lds.S
@@ -17,7 +17,7 @@ ENTRY(_start)

SECTIONS
{
- PROVIDE(_vdso_datapage = . - PAGE_SIZE);
+ PROVIDE(_vdso_datapage = . - 2 * PAGE_SIZE);
. = SIZEOF_HEADERS;

.hash : { *(.hash) } :text
--
2.25.0