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

Palmer Dabbelt palmer at dabbelt.com
Thu Sep 15 11:02:19 PDT 2022


On Thu, 08 Sep 2022 08:04:21 PDT (-0700), jszhang at kernel.org 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.

Makes sense, but I think there's a lot more diff here than we need in 
order to just fix the bug.  Does something like the following still fix 
it?  Also at kernel.org/palmer/vdso-fix-v3 .  Maybe it's a bit pedantic 
, but this late in the cycle with everyone traveling I'd prefer to keep 
the fixes smaller when possible.

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..58b8d73a4b1f 100644
--- a/arch/riscv/kernel/vdso.c
+++ b/arch/riscv/kernel/vdso.c
@@ -23,8 +23,10 @@ struct vdso_data {
 #endif

 extern char vdso_start[], vdso_end[];
+static struct __vdso_info vdso_info;
 #ifdef CONFIG_COMPAT
 extern char compat_vdso_start[], compat_vdso_end[];
+static struct __vdso_info compat_vdso_info;
 #endif

 enum vvar_pages {
@@ -114,15 +116,18 @@ 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))
+		if (vma_is_special_mapping(vma, vdso_info.dm))
 			zap_page_range(vma, vma->vm_start, size);
+#ifdef CONFIG_COMPAT
+		if (vma_is_special_mapping(vma, compat_vdso_info.dm))
+			zap_page_range(vma, vma->vm_start, size);
+#endif
 	}

 	mmap_read_unlock(mm);
@@ -264,7 +269,6 @@ static int __setup_additional_pages(struct mm_struct *mm,

 	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,

>
> Signed-off-by: Jisheng Zhang <jszhang at kernel.org>
> 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;



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