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[PATCH v2 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier

Baoquan He posted 7 patches 8 months, 3 weeks ago
There is a newer version of this series
[PATCH v2 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier
Posted by Baoquan He 8 months, 3 weeks ago 
In __get_user_pages(), it will traverse page table and take a reference
to the page the given user address corresponds to if GUP_GET or GUP_PIN
is et. However, it's not supported both GUP_GET and GUP_PIN are set.
This check should be done earlier, but not doing it till entering into
follow_page_pte() and failed.

Here move the checking to the beginning of __get_user_pages().

Signed-off-by: Baoquan He <bhe@redhat.com>
---
v1->v2:
- Fix code bug caused by copy-and-paste error, this is reported by
  lkp test robot.

 mm/gup.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 73777b1de679..f9bce14ed3cd 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -847,11 +847,6 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
 	pte_t *ptep, pte;
 	int ret;
 
-	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
-	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
-			 (FOLL_PIN | FOLL_GET)))
-		return ERR_PTR(-EINVAL);
-
 	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
 	if (!ptep)
 		return no_page_table(vma, flags, address);
@@ -1434,6 +1429,11 @@ static long __get_user_pages(struct mm_struct *mm,
 
 	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
 
+	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
+	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
+			 (FOLL_PIN | FOLL_GET)))
+		return -EINVAL;
+
 	do {
 		struct page *page;
 		unsigned int page_increm;
-- 
2.41.0
Re: [PATCH v2 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier
Posted by David Hildenbrand 8 months, 3 weeks ago 
On 31.03.25 10:13, Baoquan He wrote:
> In __get_user_pages(), it will traverse page table and take a reference
> to the page the given user address corresponds to if GUP_GET or GUP_PIN
> is et. However, it's not supported both GUP_GET and GUP_PIN are set.
> This check should be done earlier, but not doing it till entering into
> follow_page_pte() and failed.
> 
> Here move the checking to the beginning of __get_user_pages().
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
> v1->v2:
> - Fix code bug caused by copy-and-paste error, this is reported by
>    lkp test robot.
> 
>   mm/gup.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 73777b1de679..f9bce14ed3cd 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -847,11 +847,6 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
>   	pte_t *ptep, pte;
>   	int ret;
>   
> -	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> -	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
> -			 (FOLL_PIN | FOLL_GET)))
> -		return ERR_PTR(-EINVAL);
> -
>   	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
>   	if (!ptep)
>   		return no_page_table(vma, flags, address);
> @@ -1434,6 +1429,11 @@ static long __get_user_pages(struct mm_struct *mm,
>   
>   	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
>   
> +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> +	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
> +			 (FOLL_PIN | FOLL_GET)))
> +		return -EINVAL;
> +

We already have that check in is_valid_gup_args(), that catches all 
external users that could possibly mess this up.

So we can just convert that into a VM_WARN_ON_ONCE(), and while doing 
that, we should convert the VM_BUG_ON() above to a VM_WARN_ON_ONCE() as 
well.

-- 
Cheers,

David / dhildenb
Re: [PATCH v2 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier
Posted by Baoquan He 8 months, 3 weeks ago 
On 04/01/25 at 10:02am, David Hildenbrand wrote:
> On 31.03.25 10:13, Baoquan He wrote:
> > In __get_user_pages(), it will traverse page table and take a reference
> > to the page the given user address corresponds to if GUP_GET or GUP_PIN
> > is et. However, it's not supported both GUP_GET and GUP_PIN are set.
> > This check should be done earlier, but not doing it till entering into
> > follow_page_pte() and failed.
> > 
> > Here move the checking to the beginning of __get_user_pages().
> > 
> > Signed-off-by: Baoquan He <bhe@redhat.com>
> > ---
> > v1->v2:
> > - Fix code bug caused by copy-and-paste error, this is reported by
> >    lkp test robot.
> > 
> >   mm/gup.c | 10 +++++-----
> >   1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 73777b1de679..f9bce14ed3cd 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -847,11 +847,6 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
> >   	pte_t *ptep, pte;
> >   	int ret;
> > -	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> > -	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
> > -			 (FOLL_PIN | FOLL_GET)))
> > -		return ERR_PTR(-EINVAL);
> > -
> >   	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
> >   	if (!ptep)
> >   		return no_page_table(vma, flags, address);
> > @@ -1434,6 +1429,11 @@ static long __get_user_pages(struct mm_struct *mm,
> >   	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
> > +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> > +	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
> > +			 (FOLL_PIN | FOLL_GET)))
> > +		return -EINVAL;
> > +
> 
> We already have that check in is_valid_gup_args(), that catches all external
> users that could possibly mess this up.

Right.

> 
> So we can just convert that into a VM_WARN_ON_ONCE(), and while doing that,
> we should convert the VM_BUG_ON() above to a VM_WARN_ON_ONCE() as well.

Sounds great to me, will put below change into this patch of v3 as suggested.
Thanks.

diff --git a/mm/gup.c b/mm/gup.c
index 9e4ed09c578b..d551da9549b1 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1427,10 +1427,10 @@ static long __get_user_pages(struct mm_struct *mm,
 
 	start = untagged_addr_remote(mm, start);
 
-	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
+	VM_WARN_ON_ONCE(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
 
 	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
-	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
+	if (VM_WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
 			 (FOLL_PIN | FOLL_GET)))
 		return -EINVAL;
Re: [PATCH v2 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier
Posted by David Hildenbrand 8 months, 3 weeks ago 
On 01.04.25 16:34, Baoquan He wrote:
> On 04/01/25 at 10:02am, David Hildenbrand wrote:
>> On 31.03.25 10:13, Baoquan He wrote:
>>> In __get_user_pages(), it will traverse page table and take a reference
>>> to the page the given user address corresponds to if GUP_GET or GUP_PIN
>>> is et. However, it's not supported both GUP_GET and GUP_PIN are set.
>>> This check should be done earlier, but not doing it till entering into
>>> follow_page_pte() and failed.
>>>
>>> Here move the checking to the beginning of __get_user_pages().
>>>
>>> Signed-off-by: Baoquan He <bhe@redhat.com>
>>> ---
>>> v1->v2:
>>> - Fix code bug caused by copy-and-paste error, this is reported by
>>>     lkp test robot.
>>>
>>>    mm/gup.c | 10 +++++-----
>>>    1 file changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/mm/gup.c b/mm/gup.c
>>> index 73777b1de679..f9bce14ed3cd 100644
>>> --- a/mm/gup.c
>>> +++ b/mm/gup.c
>>> @@ -847,11 +847,6 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
>>>    	pte_t *ptep, pte;
>>>    	int ret;
>>> -	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
>>> -	if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) ==
>>> -			 (FOLL_PIN | FOLL_GET)))
>>> -		return ERR_PTR(-EINVAL);
>>> -
>>>    	ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
>>>    	if (!ptep)
>>>    		return no_page_table(vma, flags, address);
>>> @@ -1434,6 +1429,11 @@ static long __get_user_pages(struct mm_struct *mm,
>>>    	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
>>> +	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
>>> +	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
>>> +			 (FOLL_PIN | FOLL_GET)))
>>> +		return -EINVAL;
>>> +
>>
>> We already have that check in is_valid_gup_args(), that catches all external
>> users that could possibly mess this up.
> 
> Right.
> 
>>
>> So we can just convert that into a VM_WARN_ON_ONCE(), and while doing that,
>> we should convert the VM_BUG_ON() above to a VM_WARN_ON_ONCE() as well.
> 
> Sounds great to me, will put below change into this patch of v3 as suggested.
> Thanks.
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 9e4ed09c578b..d551da9549b1 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1427,10 +1427,10 @@ static long __get_user_pages(struct mm_struct *mm,
>   
>   	start = untagged_addr_remote(mm, start);
>   
> -	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
> +	VM_WARN_ON_ONCE(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
>   
>   	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> -	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
> +	if (VM_WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
>   			 (FOLL_PIN | FOLL_GET)))

That won't work (or shouldn't work :) ). Just drop the handling, it's a 
sanity check we don't expect to ever trigger, just like the old 
VM_BUG_ON above.

-- 
Cheers,

David / dhildenb
Re: [PATCH v2 2/7] mm/gup: check if both GUP_GET and GUP_PIN are set in __get_user_pages() earlier
Posted by Baoquan He 8 months, 3 weeks ago 
On 04/01/25 at 04:37pm, David Hildenbrand wrote:
> On 01.04.25 16:34, Baoquan He wrote:
> > On 04/01/25 at 10:02am, David Hildenbrand wrote:
> > > On 31.03.25 10:13, Baoquan He wrote:
...snip...
> > > We already have that check in is_valid_gup_args(), that catches all external
> > > users that could possibly mess this up.
> > 
> > Right.
> > 
> > > 
> > > So we can just convert that into a VM_WARN_ON_ONCE(), and while doing that,
> > > we should convert the VM_BUG_ON() above to a VM_WARN_ON_ONCE() as well.
> > 
> > Sounds great to me, will put below change into this patch of v3 as suggested.
> > Thanks.
> > 
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 9e4ed09c578b..d551da9549b1 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -1427,10 +1427,10 @@ static long __get_user_pages(struct mm_struct *mm,
> >   	start = untagged_addr_remote(mm, start);
> > -	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
> > +	VM_WARN_ON_ONCE(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
> >   	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
> > -	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
> > +	if (VM_WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
> >   			 (FOLL_PIN | FOLL_GET)))
> 
> That won't work (or shouldn't work :) ). Just drop the handling, it's a
> sanity check we don't expect to ever trigger, just like the old VM_BUG_ON
> above.

Ah, I misunderstood it. Will add below change into this patch of v3.

diff --git a/mm/gup.c b/mm/gup.c
index 9e4ed09c578b..a8a10a8ebf14 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1427,12 +1427,9 @@ static long __get_user_pages(struct mm_struct *mm,
 
 	start = untagged_addr_remote(mm, start);
 
-	VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
-
-	/* FOLL_GET and FOLL_PIN are mutually exclusive. */
-	if (WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
-			 (FOLL_PIN | FOLL_GET)))
-		return -EINVAL;
+	VM_WARN_ON_ONCE(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN)));
+	VM_WARN_ON_ONCE((gup_flags & (FOLL_PIN | FOLL_GET)) ==
+			(FOLL_PIN | FOLL_GET));
 
 	do {
 		struct page *page;

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