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

Vincenzo Frascino
2021-04-12T13:01:05Z

On 3/31/21 5:48 PM, Christophe Leroy wrote:
> 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>

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> # vDSO parts

> ---
> 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
>

--
Regards,
Vincenzo