Re: [PATCHv8 1/2] x86/vdso: add mremap hook to vm_special_mapping

[Andy Lutomirski <luto@amacapital.net>]

On Mon, Apr 25, 2016 at 4:37 AM, Dmitry Safonov <dsafonov@virtuozzo.com> wrote:
> Add possibility for userspace 32-bit applications to move
> vdso mapping. Previously, when userspace app called
> mremap for vdso, in return path it would land on previous
> address of vdso page, resulting in segmentation violation.
> Now it lands fine and returns to userspace with remapped vdso.
> This will also fix context.vdso pointer for 64-bit, which does not
> affect the user of vdso after mremap by now, but this may change.
>
> As suggested by Andy, return EINVAL for mremap that splits vdso image.
>
> Renamed and moved text_mapping structure declaration inside
> map_vdso, as it used only there and now it complement
> vvar_mapping variable.
>
> There is still problem for remapping vdso in glibc applications:
> linker relocates addresses for syscalls on vdso page, so
> you need to relink with the new addresses. Or the next syscall
> through glibc may fail:
>   Program received signal SIGSEGV, Segmentation fault.
>   #0  0xf7fd9b80 in __kernel_vsyscall ()
>   #1  0xf7ec8238 in _exit () from /usr/lib32/libc.so.6

Acked-by: Andy Lutomirski <luto@kernel.org>

Ingo, can you apply this?


>
> Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
> ---
> v8: add WARN_ON_ONCE on current->mm != new_vma->vm_mm
> v7: build fix
> v6: moved vdso_image_32 check and fixup code into vdso_fix_landing function
>     with ifdefs around
> v5: as Andy suggested, add a check that new_vma->vm_mm and current->mm are
>     the same, also check not only in_ia32_syscall() but image == &vdso_image_32
> v4: drop __maybe_unused & use image from mm->context instead vdso_image_32
> v3: as Andy suggested, return EINVAL in case of splitting vdso blob on mremap;
>     used is_ia32_task instead of ifdefs
> v2: added __maybe_unused for pt_regs in vdso_mremap
>
>  arch/x86/entry/vdso/vma.c | 47 ++++++++++++++++++++++++++++++++++++++++++-----
>  include/linux/mm_types.h  |  3 +++
>  mm/mmap.c                 | 10 ++++++++++
>  3 files changed, 55 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index 10f704584922..0625b66e5648 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -12,6 +12,7 @@
>  #include <linux/random.h>
>  #include <linux/elf.h>
>  #include <linux/cpu.h>
> +#include <linux/ptrace.h>
>  #include <asm/pvclock.h>
>  #include <asm/vgtod.h>
>  #include <asm/proto.h>
> @@ -98,10 +99,40 @@ static int vdso_fault(const struct vm_special_mapping *sm,
>         return 0;
>  }
>
> -static const struct vm_special_mapping text_mapping = {
> -       .name = "[vdso]",
> -       .fault = vdso_fault,
> -};
> +static void vdso_fix_landing(const struct vdso_image *image,
> +               struct vm_area_struct *new_vma)
> +{
> +#if defined CONFIG_X86_32 || defined CONFIG_IA32_EMULATION
> +       if (in_ia32_syscall() && image == &vdso_image_32) {
> +               struct pt_regs *regs = current_pt_regs();
> +               unsigned long vdso_land = image->sym_int80_landing_pad;
> +               unsigned long old_land_addr = vdso_land +
> +                       (unsigned long)current->mm->context.vdso;
> +
> +               /* Fixing userspace landing - look at do_fast_syscall_32 */
> +               if (regs->ip == old_land_addr)
> +                       regs->ip = new_vma->vm_start + vdso_land;
> +       }
> +#endif
> +}
> +
> +static int vdso_mremap(const struct vm_special_mapping *sm,
> +               struct vm_area_struct *new_vma)
> +{
> +       unsigned long new_size = new_vma->vm_end - new_vma->vm_start;
> +       const struct vdso_image *image = current->mm->context.vdso_image;
> +
> +       if (image->size != new_size)
> +               return -EINVAL;
> +
> +       if (WARN_ON_ONCE(current->mm != new_vma->vm_mm))
> +               return -EFAULT;
> +
> +       vdso_fix_landing(image, new_vma);
> +       current->mm->context.vdso = (void __user *)new_vma->vm_start;
> +
> +       return 0;
> +}
>
>  static int vvar_fault(const struct vm_special_mapping *sm,
>                       struct vm_area_struct *vma, struct vm_fault *vmf)
> @@ -162,6 +193,12 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
>         struct vm_area_struct *vma;
>         unsigned long addr, text_start;
>         int ret = 0;
> +
> +       static const struct vm_special_mapping vdso_mapping = {
> +               .name = "[vdso]",
> +               .fault = vdso_fault,
> +               .mremap = vdso_mremap,
> +       };
>         static const struct vm_special_mapping vvar_mapping = {
>                 .name = "[vvar]",
>                 .fault = vvar_fault,
> @@ -195,7 +232,7 @@ static int map_vdso(const struct vdso_image *image, bool calculate_addr)
>                                        image->size,
>                                        VM_READ|VM_EXEC|
>                                        VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
> -                                      &text_mapping);
> +                                      &vdso_mapping);
>
>         if (IS_ERR(vma)) {
>                 ret = PTR_ERR(vma);
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index c2d75b4fa86c..4d16ab9287af 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -586,6 +586,9 @@ struct vm_special_mapping {
>         int (*fault)(const struct vm_special_mapping *sm,
>                      struct vm_area_struct *vma,
>                      struct vm_fault *vmf);
> +
> +       int (*mremap)(const struct vm_special_mapping *sm,
> +                    struct vm_area_struct *new_vma);
>  };
>
>  enum tlb_flush_reason {
> diff --git a/mm/mmap.c b/mm/mmap.c
> index bd2e1a533bc1..ba71658dd1a1 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2930,9 +2930,19 @@ static const char *special_mapping_name(struct vm_area_struct *vma)
>         return ((struct vm_special_mapping *)vma->vm_private_data)->name;
>  }
>
> +static int special_mapping_mremap(struct vm_area_struct *new_vma)
> +{
> +       struct vm_special_mapping *sm = new_vma->vm_private_data;
> +
> +       if (sm->mremap)
> +               return sm->mremap(sm, new_vma);
> +       return 0;
> +}
> +
>  static const struct vm_operations_struct special_mapping_vmops = {
>         .close = special_mapping_close,
>         .fault = special_mapping_fault,
> +       .mremap = special_mapping_mremap,
>         .name = special_mapping_name,
>  };
>
> --
> 2.8.0
>



-- 
Andy Lutomirski
AMA Capital Management, LLC