[PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

[PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

[Barry Song]

gug prohibits users from calling get_user_pages() with FOLL_PIN. But it
allows users to call get_user_pages() with FOLL_LONGTERM only. It seems
insensible.

since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit
users from calling get_user_pages() with FOLL_LONGTERM while not with
FOLL_PIN.

mm/gup_benchmark.c used to be the only user who did this improperly.
But it has been fixed by moving to use pin_user_pages().

Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
---
 mm/gup.c | 37 ++++++++++++++++++++++---------------
 1 file changed, 22 insertions(+), 15 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index ae096ea7583f..4da669f79566 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1789,6 +1789,25 @@ static long __get_user_pages_remote(struct mm_struct *mm,
 				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
 }
 
+static bool is_valid_gup_flags(unsigned int gup_flags)
+{
+	/*
+	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
+	 * never directly by the caller, so enforce that with an assertion:
+	 */
+	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+		return false;
+	/*
+	 * FOLL_PIN is a prerequisite to FOLL_LONGTERM. Another way of saying
+	 * that is, FOLL_LONGTERM is a specific case, more restrictive case of
+	 * FOLL_PIN.
+	 */
+	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
+		return false;
+
+	return true;
+}
+
 /**
  * get_user_pages_remote() - pin user pages in memory
  * @mm:		mm_struct of target mm
@@ -1854,11 +1873,7 @@ long get_user_pages_remote(struct mm_struct *mm,
 		unsigned int gup_flags, struct page **pages,
 		struct vm_area_struct **vmas, int *locked)
 {
-	/*
-	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
-	 * never directly by the caller, so enforce that with an assertion:
-	 */
-	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+	if (!is_valid_gup_flags(gup_flags))
 		return -EINVAL;
 
 	return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
@@ -1904,11 +1919,7 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
 		unsigned int gup_flags, struct page **pages,
 		struct vm_area_struct **vmas)
 {
-	/*
-	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
-	 * never directly by the caller, so enforce that with an assertion:
-	 */
-	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+	if (!is_valid_gup_flags(gup_flags))
 		return -EINVAL;
 
 	return __gup_longterm_locked(current->mm, start, nr_pages,
@@ -2810,11 +2821,7 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
 int get_user_pages_fast(unsigned long start, int nr_pages,
 			unsigned int gup_flags, struct page **pages)
 {
-	/*
-	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
-	 * never directly by the caller, so enforce that:
-	 */
-	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
+	if (!is_valid_gup_flags(gup_flags))
 		return -EINVAL;
 
 	/*
-- 
2.27.0

Re: [PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

[Ira Weiny]

On Wed, Aug 19, 2020 at 11:01:00PM +1200, Barry Song wrote:
> gug prohibits users from calling get_user_pages() with FOLL_PIN. But it
> allows users to call get_user_pages() with FOLL_LONGTERM only. It seems
> insensible.
> 
> since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit
> users from calling get_user_pages() with FOLL_LONGTERM while not with
> FOLL_PIN.
> 
> mm/gup_benchmark.c used to be the only user who did this improperly.
> But it has been fixed by moving to use pin_user_pages().
> 
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>

Seems reasonable to me.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

> ---
>  mm/gup.c | 37 ++++++++++++++++++++++---------------
>  1 file changed, 22 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index ae096ea7583f..4da669f79566 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1789,6 +1789,25 @@ static long __get_user_pages_remote(struct mm_struct *mm,
>  				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
>  }
>  
> +static bool is_valid_gup_flags(unsigned int gup_flags)
> +{
> +	/*
> +	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> +	 * never directly by the caller, so enforce that with an assertion:
> +	 */
> +	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +		return false;
> +	/*
> +	 * FOLL_PIN is a prerequisite to FOLL_LONGTERM. Another way of saying
> +	 * that is, FOLL_LONGTERM is a specific case, more restrictive case of
> +	 * FOLL_PIN.
> +	 */
> +	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
> +		return false;
> +
> +	return true;
> +}
> +
>  /**
>   * get_user_pages_remote() - pin user pages in memory
>   * @mm:		mm_struct of target mm
> @@ -1854,11 +1873,7 @@ long get_user_pages_remote(struct mm_struct *mm,
>  		unsigned int gup_flags, struct page **pages,
>  		struct vm_area_struct **vmas, int *locked)
>  {
> -	/*
> -	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> -	 * never directly by the caller, so enforce that with an assertion:
> -	 */
> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +	if (!is_valid_gup_flags(gup_flags))
>  		return -EINVAL;
>  
>  	return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
> @@ -1904,11 +1919,7 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
>  		unsigned int gup_flags, struct page **pages,
>  		struct vm_area_struct **vmas)
>  {
> -	/*
> -	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> -	 * never directly by the caller, so enforce that with an assertion:
> -	 */
> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +	if (!is_valid_gup_flags(gup_flags))
>  		return -EINVAL;
>  
>  	return __gup_longterm_locked(current->mm, start, nr_pages,
> @@ -2810,11 +2821,7 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
>  int get_user_pages_fast(unsigned long start, int nr_pages,
>  			unsigned int gup_flags, struct page **pages)
>  {
> -	/*
> -	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> -	 * never directly by the caller, so enforce that:
> -	 */
> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +	if (!is_valid_gup_flags(gup_flags))
>  		return -EINVAL;
>  
>  	/*
> -- 
> 2.27.0
> 
> 
> 

Re: [PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

[John Hubbard]

On 8/19/20 4:01 AM, Barry Song wrote:
> gug prohibits users from calling get_user_pages() with FOLL_PIN. But it

Maybe Andrew can fix the typo above: gug --> gup.


> allows users to call get_user_pages() with FOLL_LONGTERM only. It seems
> insensible.
> 
> since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit
> users from calling get_user_pages() with FOLL_LONGTERM while not with
> FOLL_PIN.
> 
> mm/gup_benchmark.c used to be the only user who did this improperly.
> But it has been fixed by moving to use pin_user_pages().

For future patches, you don't have to write everything in the
commit log. Some things are better placed in a cover letter or after
the "---" line, because they don't need to be recorded forever.

Anyway, the diffs seem fine, assuming that you've audited the call sites.

thanks,
-- 
John Hubbard
NVIDIA

> 
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Jérôme Glisse <jglisse@redhat.com>
> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: Jason Gunthorpe <jgg@ziepe.ca>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Shuah Khan <shuah@kernel.org>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> ---
>   mm/gup.c | 37 ++++++++++++++++++++++---------------
>   1 file changed, 22 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index ae096ea7583f..4da669f79566 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1789,6 +1789,25 @@ static long __get_user_pages_remote(struct mm_struct *mm,
>   				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
>   }
>   
> +static bool is_valid_gup_flags(unsigned int gup_flags)
> +{
> +	/*
> +	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> +	 * never directly by the caller, so enforce that with an assertion:
> +	 */
> +	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +		return false;
> +	/*
> +	 * FOLL_PIN is a prerequisite to FOLL_LONGTERM. Another way of saying
> +	 * that is, FOLL_LONGTERM is a specific case, more restrictive case of
> +	 * FOLL_PIN.
> +	 */
> +	if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
> +		return false;
> +
> +	return true;
> +}
> +
>   /**
>    * get_user_pages_remote() - pin user pages in memory
>    * @mm:		mm_struct of target mm
> @@ -1854,11 +1873,7 @@ long get_user_pages_remote(struct mm_struct *mm,
>   		unsigned int gup_flags, struct page **pages,
>   		struct vm_area_struct **vmas, int *locked)
>   {
> -	/*
> -	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> -	 * never directly by the caller, so enforce that with an assertion:
> -	 */
> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +	if (!is_valid_gup_flags(gup_flags))
>   		return -EINVAL;
>   
>   	return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
> @@ -1904,11 +1919,7 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
>   		unsigned int gup_flags, struct page **pages,
>   		struct vm_area_struct **vmas)
>   {
> -	/*
> -	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> -	 * never directly by the caller, so enforce that with an assertion:
> -	 */
> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +	if (!is_valid_gup_flags(gup_flags))
>   		return -EINVAL;
>   
>   	return __gup_longterm_locked(current->mm, start, nr_pages,
> @@ -2810,11 +2821,7 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
>   int get_user_pages_fast(unsigned long start, int nr_pages,
>   			unsigned int gup_flags, struct page **pages)
>   {
> -	/*
> -	 * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> -	 * never directly by the caller, so enforce that:
> -	 */
> -	if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> +	if (!is_valid_gup_flags(gup_flags))
>   		return -EINVAL;
>   
>   	/*
> 

Re: [PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

[Souptick Joarder]

On Wed, Aug 19, 2020 at 11:45 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 8/19/20 4:01 AM, Barry Song wrote:
> > gug prohibits users from calling get_user_pages() with FOLL_PIN. But it
>
> Maybe Andrew can fix the typo above: gug --> gup.
>
>
> > allows users to call get_user_pages() with FOLL_LONGTERM only. It seems
> > insensible.
> >
> > since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit
> > users from calling get_user_pages() with FOLL_LONGTERM while not with
> > FOLL_PIN.
> >
> > mm/gup_benchmark.c used to be the only user who did this improperly.
> > But it has been fixed by moving to use pin_user_pages().
>
> For future patches, you don't have to write everything in the
> commit log. Some things are better placed in a cover letter or after
> the "---" line, because they don't need to be recorded forever.
>
> Anyway, the diffs seem fine, assuming that you've audited the call sites.

We can use is_valid_gup_flags() inside ->
get_user_pages_locked(),
get_user_pages_unlocked(),
pin_user_pages_locked() as well.

Are you planning to add it in future patches ?

>
> thanks,
> --
> John Hubbard
> NVIDIA
>
> >
> > Cc: John Hubbard <jhubbard@nvidia.com>
> > Cc: Jan Kara <jack@suse.cz>
> > Cc: Jérôme Glisse <jglisse@redhat.com>
> > Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> > Cc: Al Viro <viro@zeniv.linux.org.uk>
> > Cc: Christoph Hellwig <hch@infradead.org>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Dave Chinner <david@fromorbit.com>
> > Cc: Jason Gunthorpe <jgg@ziepe.ca>
> > Cc: Jonathan Corbet <corbet@lwn.net>
> > Cc: Michal Hocko <mhocko@suse.com>
> > Cc: Mike Kravetz <mike.kravetz@oracle.com>
> > Cc: Shuah Khan <shuah@kernel.org>
> > Cc: Vlastimil Babka <vbabka@suse.cz>
> > Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
> > ---
> >   mm/gup.c | 37 ++++++++++++++++++++++---------------
> >   1 file changed, 22 insertions(+), 15 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index ae096ea7583f..4da669f79566 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1789,6 +1789,25 @@ static long __get_user_pages_remote(struct mm_struct *mm,
> >                                      gup_flags | FOLL_TOUCH | FOLL_REMOTE);
> >   }
> >
> > +static bool is_valid_gup_flags(unsigned int gup_flags)
> > +{
> > +     /*
> > +      * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> > +      * never directly by the caller, so enforce that with an assertion:
> > +      */
> > +     if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> > +             return false;
> > +     /*
> > +      * FOLL_PIN is a prerequisite to FOLL_LONGTERM. Another way of saying
> > +      * that is, FOLL_LONGTERM is a specific case, more restrictive case of
> > +      * FOLL_PIN.
> > +      */
> > +     if (WARN_ON_ONCE(gup_flags & FOLL_LONGTERM))
> > +             return false;
> > +
> > +     return true;
> > +}
> > +
> >   /**
> >    * get_user_pages_remote() - pin user pages in memory
> >    * @mm:             mm_struct of target mm
> > @@ -1854,11 +1873,7 @@ long get_user_pages_remote(struct mm_struct *mm,
> >               unsigned int gup_flags, struct page **pages,
> >               struct vm_area_struct **vmas, int *locked)
> >   {
> > -     /*
> > -      * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> > -      * never directly by the caller, so enforce that with an assertion:
> > -      */
> > -     if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> > +     if (!is_valid_gup_flags(gup_flags))
> >               return -EINVAL;
> >
> >       return __get_user_pages_remote(mm, start, nr_pages, gup_flags,
> > @@ -1904,11 +1919,7 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
> >               unsigned int gup_flags, struct page **pages,
> >               struct vm_area_struct **vmas)
> >   {
> > -     /*
> > -      * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> > -      * never directly by the caller, so enforce that with an assertion:
> > -      */
> > -     if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> > +     if (!is_valid_gup_flags(gup_flags))
> >               return -EINVAL;
> >
> >       return __gup_longterm_locked(current->mm, start, nr_pages,
> > @@ -2810,11 +2821,7 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast_only);
> >   int get_user_pages_fast(unsigned long start, int nr_pages,
> >                       unsigned int gup_flags, struct page **pages)
> >   {
> > -     /*
> > -      * FOLL_PIN must only be set internally by the pin_user_pages*() APIs,
> > -      * never directly by the caller, so enforce that:
> > -      */
> > -     if (WARN_ON_ONCE(gup_flags & FOLL_PIN))
> > +     if (!is_valid_gup_flags(gup_flags))
> >               return -EINVAL;
> >
> >       /*
> >
>
>

Re: [PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

[John Hubbard]

On 9/3/20 12:12 AM, Souptick Joarder wrote:
> On Wed, Aug 19, 2020 at 11:45 PM John Hubbard <jhubbard@nvidia.com> wrote:
>>
>> On 8/19/20 4:01 AM, Barry Song wrote:
>>> gug prohibits users from calling get_user_pages() with FOLL_PIN. But it
>>
>> Maybe Andrew can fix the typo above: gug --> gup.
>>
>>
>>> allows users to call get_user_pages() with FOLL_LONGTERM only. It seems
>>> insensible.
>>>
>>> since FOLL_LONGTERM is a stricter case of FOLL_PIN, we should prohibit
>>> users from calling get_user_pages() with FOLL_LONGTERM while not with
>>> FOLL_PIN.
>>>
>>> mm/gup_benchmark.c used to be the only user who did this improperly.
>>> But it has been fixed by moving to use pin_user_pages().
>>
>> For future patches, you don't have to write everything in the
>> commit log. Some things are better placed in a cover letter or after
>> the "---" line, because they don't need to be recorded forever.
>>
>> Anyway, the diffs seem fine, assuming that you've audited the call sites.
> 
> We can use is_valid_gup_flags() inside ->
> get_user_pages_locked(),
> get_user_pages_unlocked(),
> pin_user_pages_locked() as well.

Probably it's best to discern between valid pup flags, and valid gup flags.
As in: separate functions for those. Maybe one is a subset of the other, but
still.

> 
> Are you planning to add it in future patches ?
> 

It's not on my list. I don't see anything wrong with doing so, other
than avoiding the minor pitfall I called out above. So if you want to
do that, then feel free...


thanks,
-- 
John Hubbard
NVIDIA

Re: [PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

[Matthew Wilcox]

On Thu, Sep 03, 2020 at 12:42:44PM +0530, Souptick Joarder wrote:
> We can use is_valid_gup_flags() inside ->
> get_user_pages_locked(),
> get_user_pages_unlocked(),
> pin_user_pages_locked() as well.
> 
> Are you planning to add it in future patches ?

If you're looking for a new project, adding a foll_t or gup_t or
something for the FOLL flags (like we have for gfp_t or vm_fault_t)
would be helpful.  We're inconsistent with our naming here.

Re: [PATCH] mm/gup: don't permit users to call get_user_pages with FOLL_LONGTERM

[Souptick Joarder]

On Fri, Sep 4, 2020 at 12:09 AM Matthew Wilcox <willy@infradead.org> wrote:
>
> On Thu, Sep 03, 2020 at 12:42:44PM +0530, Souptick Joarder wrote:
> > We can use is_valid_gup_flags() inside ->
> > get_user_pages_locked(),
> > get_user_pages_unlocked(),
> > pin_user_pages_locked() as well.
> >
> > Are you planning to add it in future patches ?
>
> If you're looking for a new project, adding a foll_t or gup_t or
> something for the FOLL flags (like we have for gfp_t or vm_fault_t)
> would be helpful.  We're inconsistent with our naming here.

Sure. I will start looking into this and come up with a RFC version.