Date:   Thu, 22 Sep 2022 09:38:48 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     jszhang@...nel.org
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        guoren@...nel.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject:     Re: [PATCH v2] riscv: vdso: fix NULL deference in vdso_join_timens() when vfork

On Thu, 22 Sep 2022 05:07:44 PDT (-0700), jszhang@...nel.org wrote:
> On Thu, Sep 15, 2022 at 11:02:19AM -0700, Palmer Dabbelt wrote:
>> On Thu, 08 Sep 2022 08:04:21 PDT (-0700), jszhang@...nel.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
>
> The reason of "a lot more diff" is moving the code to avoid forward declaration.
> If you prefer smaller fix, I can provide a simpler one w/ forware
> declaration. And provide a new clean up patch for next window, what do you
> think?

Works for me.  If you put the two back-to-back on 6.0-rc1 then I can 
avoid the merge conflict.  Thanks!

>
> Thanks
>> 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@...nel.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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