Re: [PATCH v2] riscv: vdso: fix NULL deference in vdso_join_timens() when vfork

[Guo Ren]

Great job! I've tested it on rv32-rootfs, and everything seems to be working.

Tested-by: Guo Ren <guoren@xxxxxxxxxx>

On Thu, Sep 8, 2022 at 11:13 PM Jisheng Zhang <jszhang@xxxxxxxxxx> wrote:
>
> Testing tools/testing/selftests/timens/vfork_exec.c got below
> kernel log:
>
> [    6.838454] Unable to handle kernel access to user memory without uaccess routines at virtual address 0000000000000020
> [    6.842255] Oops [#1]
> [    6.842871] Modules linked in:
> [    6.844249] CPU: 1 PID: 64 Comm: vfork_exec Not tainted 6.0.0-rc3-rt15+ #8
> [    6.845861] Hardware name: riscv-virtio,qemu (DT)
> [    6.848009] epc : vdso_join_timens+0xd2/0x110
> [    6.850097]  ra : vdso_join_timens+0xd2/0x110
> [    6.851164] epc : ffffffff8000635c ra : ffffffff8000635c sp : ff6000000181fbf0
> [    6.852562]  gp : ffffffff80cff648 tp : ff60000000fdb700 t0 : 3030303030303030
> [    6.853852]  t1 : 0000000000000030 t2 : 3030303030303030 s0 : ff6000000181fc40
> [    6.854984]  s1 : ff60000001e6c000 a0 : 0000000000000010 a1 : ffffffff8005654c
> [    6.856221]  a2 : 00000000ffffefff a3 : 0000000000000000 a4 : 0000000000000000
> [    6.858114]  a5 : 0000000000000000 a6 : 0000000000000008 a7 : 0000000000000038
> [    6.859484]  s2 : ff60000001e6c068 s3 : ff6000000108abb0 s4 : 0000000000000000
> [    6.860751]  s5 : 0000000000001000 s6 : ffffffff8089dc40 s7 : ffffffff8089dc38
> [    6.862029]  s8 : ffffffff8089dc30 s9 : ff60000000fdbe38 s10: 000000000000005e
> [    6.863304]  s11: ffffffff80cc3510 t3 : ffffffff80d1112f t4 : ffffffff80d1112f
> [    6.864565]  t5 : ffffffff80d11130 t6 : ff6000000181fa00
> [    6.865561] status: 0000000000000120 badaddr: 0000000000000020 cause: 000000000000000d
> [    6.868046] [<ffffffff8008dc94>] timens_commit+0x38/0x11a
> [    6.869089] [<ffffffff8008dde8>] timens_on_fork+0x72/0xb4
> [    6.870055] [<ffffffff80190096>] begin_new_exec+0x3c6/0x9f0
> [    6.871231] [<ffffffff801d826c>] load_elf_binary+0x628/0x1214
> [    6.872304] [<ffffffff8018ee7a>] bprm_execve+0x1f2/0x4e4
> [    6.873243] [<ffffffff8018f90c>] do_execveat_common+0x16e/0x1ee
> [    6.874258] [<ffffffff8018f9c8>] sys_execve+0x3c/0x48
> [    6.875162] [<ffffffff80003556>] ret_from_syscall+0x0/0x2
> [    6.877484] ---[ end trace 0000000000000000 ]---
>
> This is because the mm->context.vdso_info is NULL in vfork case. From
> another side, mm->context.vdso_info either points to vdso info
> for RV64 or vdso info for compat, there's no need to bloat riscv's
> mm_context_t, we can handle the difference when setup the additional
> page for vdso.
>
> Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
> Fixes: 3092eb456375 ("riscv: compat: vdso: Add setup additional pages implementation")
> ---
>
> since v1:
>  - add "Fixes" tag
>  - fix build error when CONFIG_COMPAT is enabled.
>
>  arch/riscv/include/asm/mmu.h |   1 -
>  arch/riscv/kernel/vdso.c     | 178 +++++++++++++++++++----------------
>  2 files changed, 95 insertions(+), 84 deletions(-)
>
> diff --git a/arch/riscv/include/asm/mmu.h b/arch/riscv/include/asm/mmu.h
> index cedcf8ea3c76..0099dc116168 100644
> --- a/arch/riscv/include/asm/mmu.h
> +++ b/arch/riscv/include/asm/mmu.h
> @@ -16,7 +16,6 @@ typedef struct {
>         atomic_long_t id;
>  #endif
>         void *vdso;
> -       void *vdso_info;
>  #ifdef CONFIG_SMP
>         /* A local icache flush is needed before user execution can resume. */
>         cpumask_t icache_stale_mask;
> diff --git a/arch/riscv/kernel/vdso.c b/arch/riscv/kernel/vdso.c
> index 69b05b6c181b..8ca3b821e1b5 100644
> --- a/arch/riscv/kernel/vdso.c
> +++ b/arch/riscv/kernel/vdso.c
> @@ -27,6 +27,11 @@ extern char vdso_start[], vdso_end[];
>  extern char compat_vdso_start[], compat_vdso_end[];
>  #endif
>
> +enum vdso_abi {
> +       VDSO_ABI_RV64,
> +       VDSO_ABI_RV32,
> +};
> +
>  enum vvar_pages {
>         VVAR_DATA_PAGE_OFFSET,
>         VVAR_TIMENS_PAGE_OFFSET,
> @@ -68,67 +73,7 @@ static int vdso_mremap(const struct vm_special_mapping *sm,
>         return 0;
>  }
>
> -static void __init __vdso_init(struct __vdso_info *vdso_info)
> -{
> -       unsigned int i;
> -       struct page **vdso_pagelist;
> -       unsigned long pfn;
> -
> -       if (memcmp(vdso_info->vdso_code_start, "\177ELF", 4))
> -               panic("vDSO is not a valid ELF object!\n");
> -
> -       vdso_info->vdso_pages = (
> -               vdso_info->vdso_code_end -
> -               vdso_info->vdso_code_start) >>
> -               PAGE_SHIFT;
> -
> -       vdso_pagelist = kcalloc(vdso_info->vdso_pages,
> -                               sizeof(struct page *),
> -                               GFP_KERNEL);
> -       if (vdso_pagelist == NULL)
> -               panic("vDSO kcalloc failed!\n");
> -
> -       /* Grab the vDSO code pages. */
> -       pfn = sym_to_pfn(vdso_info->vdso_code_start);
> -
> -       for (i = 0; i < vdso_info->vdso_pages; i++)
> -               vdso_pagelist[i] = pfn_to_page(pfn + i);
> -
> -       vdso_info->cm->pages = vdso_pagelist;
> -}
> -
>  #ifdef CONFIG_TIME_NS
> -struct vdso_data *arch_get_vdso_data(void *vvar_page)
> -{
> -       return (struct vdso_data *)(vvar_page);
> -}
> -
> -/*
> - * 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;
> -       struct __vdso_info *vdso_info = mm->context.vdso_info;
> -
> -       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, vdso_info->dm))
> -                       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))
> @@ -197,13 +142,6 @@ static struct vm_special_mapping rv_vdso_maps[] __ro_after_init = {
>         },
>  };
>
> -static struct __vdso_info vdso_info __ro_after_init = {
> -       .name = "vdso",
> -       .vdso_code_start = vdso_start,
> -       .vdso_code_end = vdso_end,
> -       .dm = &rv_vdso_maps[RV_VDSO_MAP_VVAR],
> -       .cm = &rv_vdso_maps[RV_VDSO_MAP_VDSO],
> -};
>
>  #ifdef CONFIG_COMPAT
>  static struct vm_special_mapping rv_compat_vdso_maps[] __ro_after_init = {
> @@ -216,21 +154,97 @@ static struct vm_special_mapping rv_compat_vdso_maps[] __ro_after_init = {
>                 .mremap = vdso_mremap,
>         },
>  };
> +#endif
>
> -static struct __vdso_info compat_vdso_info __ro_after_init = {
> -       .name = "compat_vdso",
> -       .vdso_code_start = compat_vdso_start,
> -       .vdso_code_end = compat_vdso_end,
> -       .dm = &rv_compat_vdso_maps[RV_VDSO_MAP_VVAR],
> -       .cm = &rv_compat_vdso_maps[RV_VDSO_MAP_VDSO],
> +static struct __vdso_info vdso_info[] __ro_after_init = {
> +       [VDSO_ABI_RV64] = {
> +               .name = "vdso",
> +               .vdso_code_start = vdso_start,
> +               .vdso_code_end = vdso_end,
> +               .dm = &rv_vdso_maps[RV_VDSO_MAP_VVAR],
> +               .cm = &rv_vdso_maps[RV_VDSO_MAP_VDSO],
> +       },
> +#ifdef CONFIG_COMPAT
> +       [VDSO_ABI_RV32] = {
> +               .name = "compat_vdso",
> +               .vdso_code_start = compat_vdso_start,
> +               .vdso_code_end = compat_vdso_end,
> +               .dm = &rv_compat_vdso_maps[RV_VDSO_MAP_VVAR],
> +               .cm = &rv_compat_vdso_maps[RV_VDSO_MAP_VDSO],
> +       },
> +#endif
>  };
> +
> +static void __init __vdso_init(enum vdso_abi abi)
> +{
> +       unsigned int i;
> +       struct page **vdso_pagelist;
> +       unsigned long pfn;
> +
> +       if (memcmp(vdso_info[abi].vdso_code_start, "\177ELF", 4))
> +               panic("vDSO is not a valid ELF object!\n");
> +
> +       vdso_info[abi].vdso_pages = (
> +               vdso_info[abi].vdso_code_end -
> +               vdso_info[abi].vdso_code_start) >>
> +               PAGE_SHIFT;
> +
> +       vdso_pagelist = kcalloc(vdso_info[abi].vdso_pages,
> +                               sizeof(struct page *),
> +                               GFP_KERNEL);
> +       if (vdso_pagelist == NULL)
> +               panic("vDSO kcalloc failed!\n");
> +
> +       /* Grab the vDSO code pages. */
> +       pfn = sym_to_pfn(vdso_info[abi].vdso_code_start);
> +
> +       for (i = 0; i < vdso_info[abi].vdso_pages; i++)
> +               vdso_pagelist[i] = pfn_to_page(pfn + i);
> +
> +       vdso_info[abi].cm->pages = vdso_pagelist;
> +}
> +
> +#ifdef CONFIG_TIME_NS
> +struct vdso_data *arch_get_vdso_data(void *vvar_page)
> +{
> +       return (struct vdso_data *)(vvar_page);
> +}
> +
> +/*
> + * 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, vdso_info[VDSO_ABI_RV64].dm))
> +                       zap_page_range(vma, vma->vm_start, size);
> +#ifdef CONFIG_COMPAT
> +               if (vma_is_special_mapping(vma, vdso_info[VDSO_ABI_RV32].dm))
> +                       zap_page_range(vma, vma->vm_start, size);
> +#endif
> +       }
> +
> +       mmap_read_unlock(mm);
> +       return 0;
> +}
>  #endif
>
>  static int __init vdso_init(void)
>  {
> -       __vdso_init(&vdso_info);
> +       __vdso_init(VDSO_ABI_RV64);
>  #ifdef CONFIG_COMPAT
> -       __vdso_init(&compat_vdso_info);
> +       __vdso_init(VDSO_ABI_RV32);
>  #endif
>
>         return 0;
> @@ -240,14 +254,14 @@ arch_initcall(vdso_init);
>  static int __setup_additional_pages(struct mm_struct *mm,
>                                     struct linux_binprm *bprm,
>                                     int uses_interp,
> -                                   struct __vdso_info *vdso_info)
> +                                   enum vdso_abi abi)
>  {
>         unsigned long vdso_base, vdso_text_len, vdso_mapping_len;
>         void *ret;
>
>         BUILD_BUG_ON(VVAR_NR_PAGES != __VVAR_PAGES);
>
> -       vdso_text_len = vdso_info->vdso_pages << PAGE_SHIFT;
> +       vdso_text_len = vdso_info[abi].vdso_pages << PAGE_SHIFT;
>         /* Be sure to map the data page */
>         vdso_mapping_len = vdso_text_len + VVAR_SIZE;
>
> @@ -258,18 +272,17 @@ static int __setup_additional_pages(struct mm_struct *mm,
>         }
>
>         ret = _install_special_mapping(mm, vdso_base, VVAR_SIZE,
> -               (VM_READ | VM_MAYREAD | VM_PFNMAP), vdso_info->dm);
> +               (VM_READ | VM_MAYREAD | VM_PFNMAP), vdso_info[abi].dm);
>         if (IS_ERR(ret))
>                 goto up_fail;
>
>         vdso_base += VVAR_SIZE;
>         mm->context.vdso = (void *)vdso_base;
> -       mm->context.vdso_info = (void *)vdso_info;
>
>         ret =
>            _install_special_mapping(mm, vdso_base, vdso_text_len,
>                 (VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC),
> -               vdso_info->cm);
> +               vdso_info[abi].cm);
>
>         if (IS_ERR(ret))
>                 goto up_fail;
> @@ -291,8 +304,7 @@ int compat_arch_setup_additional_pages(struct linux_binprm *bprm,
>         if (mmap_write_lock_killable(mm))
>                 return -EINTR;
>
> -       ret = __setup_additional_pages(mm, bprm, uses_interp,
> -                                                       &compat_vdso_info);
> +       ret = __setup_additional_pages(mm, bprm, uses_interp, VDSO_ABI_RV32);
>         mmap_write_unlock(mm);
>
>         return ret;
> @@ -307,7 +319,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
>         if (mmap_write_lock_killable(mm))
>                 return -EINTR;
>
> -       ret = __setup_additional_pages(mm, bprm, uses_interp, &vdso_info);
> +       ret = __setup_additional_pages(mm, bprm, uses_interp, VDSO_ABI_RV64);
>         mmap_write_unlock(mm);
>
>         return ret;
> --
> 2.34.1
>


-- 
Best Regards
 Guo Ren