[PATCH v2 1/1] check that order of free pages falls within valid range

[PATCH v2 1/1] check that order of free pages falls within valid range

[Alexander Egorenkov]

This change makes __exclude_unnecessary_pages() more robust by
verifying that the order of a free page is valid before computing the size
of its memory block in the buddy system.

The order of a free page cannot be larger than (MAX_ORDER - 1) because
the array 'zone.free_area' is of size MAX_ORDER.

This situation is reproducible with some s390x dumps:

__exclude_unnecessary_pages: Invalid free page order: pfn=2690c0, order=52, max order=8

References:
- https://listman.redhat.com/archives/crash-utility/2021-September/009204.html
- https://www.kernel.org/doc/gorman/html/understand/understand009.html

Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
---
 makedumpfile.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/makedumpfile.c b/makedumpfile.c
index 2ef345879524..56aa026e7b34 100644
--- a/makedumpfile.c
+++ b/makedumpfile.c
@@ -6457,6 +6457,12 @@ __exclude_unnecessary_pages(unsigned long mem_map,
 		else if ((info->dump_level & DL_EXCLUDE_FREE)
 		    && info->page_is_buddy
 		    && info->page_is_buddy(flags, _mapcount, private, _count)) {
+			if (private >= ARRAY_LENGTH(zone.free_area)) {
+				ERRMSG("Invalid free page order: pfn=%llx, order=%lu, max order=%lu\n",
+				       pfn, private, ARRAY_LENGTH(zone.free_area) - 1);
+				free(page_cache);
+				return FALSE;
+			}
 			nr_pages = 1 << private;
 			pfn_counter = &pfn_free;
 		}
-- 
2.34.1

[PATCH v2 1/1] check that order of free pages falls within valid range

[Alexander Egorenkov]

Alexander Egorenkov <egorenar@linux.ibm.com> writes:

> This change makes __exclude_unnecessary_pages() more robust by
> verifying that the order of a free page is valid before computing the size
> of its memory block in the buddy system.
>
> The order of a free page cannot be larger than (MAX_ORDER - 1) because
> the array 'zone.free_area' is of size MAX_ORDER.
>
> This situation is reproducible with some s390x dumps:
>
> __exclude_unnecessary_pages: Invalid free page order: pfn=2690c0, order=52, max order=8
>
> References:
> - https://listman.redhat.com/archives/crash-utility/2021-September/009204.html
> - https://www.kernel.org/doc/gorman/html/understand/understand009.html
>
> Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
> ---
>  makedumpfile.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/makedumpfile.c b/makedumpfile.c
> index 2ef345879524..56aa026e7b34 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -6457,6 +6457,12 @@ __exclude_unnecessary_pages(unsigned long mem_map,
>  		else if ((info->dump_level & DL_EXCLUDE_FREE)
>  		    && info->page_is_buddy
>  		    && info->page_is_buddy(flags, _mapcount, private, _count)) {
> +			if (private >= ARRAY_LENGTH(zone.free_area)) {
> +				ERRMSG("Invalid free page order: pfn=%llx, order=%lu, max order=%lu\n",
> +				       pfn, private, ARRAY_LENGTH(zone.free_area) - 1);
> +				free(page_cache);
> +				return FALSE;
> +			}
>  			nr_pages = 1 << private;
>  			pfn_counter = &pfn_free;
>  		}
> -- 
> 2.34.1
>
>
> _______________________________________________
> kexec mailing list
> kexec at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec

I found out when this can happen.

If e.g. a driver calls free_pages() and gives an order > max page order,
then __free_one_page() stores the given invalid page order in the
'private' member of struct page and gives it back to the buddy
allocator.

This is what actually happened in the dump i used to reproduce this issue
with makedumpfile.

Regards
Alex
 

[PATCH v2 1/1] check that order of free pages falls within valid range

[HAGIO KAZUHITO =?unknown-8bit?b?6JCp5bC+IOS4gOS7gQ==?=]

Hi Alex,

thanks for the patch,

-----Original Message-----
> Alexander Egorenkov <egorenar@linux.ibm.com> writes:
> 
> > This change makes __exclude_unnecessary_pages() more robust by
> > verifying that the order of a free page is valid before computing the size
> > of its memory block in the buddy system.
> >
> > The order of a free page cannot be larger than (MAX_ORDER - 1) because
> > the array 'zone.free_area' is of size MAX_ORDER.
> >
> > This situation is reproducible with some s390x dumps:
> >
> > __exclude_unnecessary_pages: Invalid free page order: pfn=2690c0, order=52, max order=8
> >
> > References:
> > - https://listman.redhat.com/archives/crash-utility/2021-September/009204.html
> > - https://www.kernel.org/doc/gorman/html/understand/understand009.html
> >
> > Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
> > ---
> >  makedumpfile.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/makedumpfile.c b/makedumpfile.c
> > index 2ef345879524..56aa026e7b34 100644
> > --- a/makedumpfile.c
> > +++ b/makedumpfile.c
> > @@ -6457,6 +6457,12 @@ __exclude_unnecessary_pages(unsigned long mem_map,
> >  		else if ((info->dump_level & DL_EXCLUDE_FREE)
> >  		    && info->page_is_buddy
> >  		    && info->page_is_buddy(flags, _mapcount, private, _count)) {
> > +			if (private >= ARRAY_LENGTH(zone.free_area)) {
> > +				ERRMSG("Invalid free page order: pfn=%llx, order=%lu, max order=%lu\n",
> > +				       pfn, private, ARRAY_LENGTH(zone.free_area) - 1);
> > +				free(page_cache);
> > +				return FALSE;
> > +			}
> >  			nr_pages = 1 << private;
> >  			pfn_counter = &pfn_free;
> >  		}
> > --
> > 2.34.1
> >
> >
> > _______________________________________________
> > kexec mailing list
> > kexec at lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> 
> I found out when this can happen.
> 
> If e.g. a driver calls free_pages() and gives an order > max page order,
> then __free_one_page() stores the given invalid page order in the
> 'private' member of struct page and gives it back to the buddy
> allocator.
> 
> This is what actually happened in the dump i used to reproduce this issue
> with makedumpfile.

Good catch, though I could not reproduce it so far..

but I wonder whether we have no other choice than returning FALSE?
in other words, can't we skip (include) the invalid page with a
warning message?

As I said before, I think that capturing more pages than expected
will be better than not capturing a dump, and that is "robust"
against unexpected values.

Thanks,
Kazu

[PATCH v2 1/1] check that order of free pages falls within valid range

[Alexander Egorenkov]

Hi Kazu,

HAGIO KAZUHITO(?????)	<k-hagio-ab@nec.com> writes:

> Hi Alex,
>
> thanks for the patch,
>
> -----Original Message-----
>> Alexander Egorenkov <egorenar@linux.ibm.com> writes:
>> 
>> > This change makes __exclude_unnecessary_pages() more robust by
>> > verifying that the order of a free page is valid before computing the size
>> > of its memory block in the buddy system.
>> >
>> > The order of a free page cannot be larger than (MAX_ORDER - 1) because
>> > the array 'zone.free_area' is of size MAX_ORDER.
>> >
>> > This situation is reproducible with some s390x dumps:
>> >
>> > __exclude_unnecessary_pages: Invalid free page order: pfn=2690c0, order=52, max order=8
>> >
>> > References:
>> > - https://listman.redhat.com/archives/crash-utility/2021-September/009204.html
>> > - https://www.kernel.org/doc/gorman/html/understand/understand009.html
>> >
>> > Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
>> > ---
>> >  makedumpfile.c | 6 ++++++
>> >  1 file changed, 6 insertions(+)
>> >
>> > diff --git a/makedumpfile.c b/makedumpfile.c
>> > index 2ef345879524..56aa026e7b34 100644
>> > --- a/makedumpfile.c
>> > +++ b/makedumpfile.c
>> > @@ -6457,6 +6457,12 @@ __exclude_unnecessary_pages(unsigned long mem_map,
>> >  		else if ((info->dump_level & DL_EXCLUDE_FREE)
>> >  		    && info->page_is_buddy
>> >  		    && info->page_is_buddy(flags, _mapcount, private, _count)) {
>> > +			if (private >= ARRAY_LENGTH(zone.free_area)) {
>> > +				ERRMSG("Invalid free page order: pfn=%llx, order=%lu, max order=%lu\n",
>> > +				       pfn, private, ARRAY_LENGTH(zone.free_area) - 1);
>> > +				free(page_cache);
>> > +				return FALSE;
>> > +			}
>> >  			nr_pages = 1 << private;
>> >  			pfn_counter = &pfn_free;
>> >  		}
>> > --
>> > 2.34.1
>> >
>> >
>> > _______________________________________________
>> > kexec mailing list
>> > kexec at lists.infradead.org
>> > http://lists.infradead.org/mailman/listinfo/kexec
>> 
>> I found out when this can happen.
>> 
>> If e.g. a driver calls free_pages() and gives an order > max page order,
>> then __free_one_page() stores the given invalid page order in the
>> 'private' member of struct page and gives it back to the buddy
>> allocator.
>> 
>> This is what actually happened in the dump i used to reproduce this issue
>> with makedumpfile.
>
> Good catch, though I could not reproduce it so far..
>
> but I wonder whether we have no other choice than returning FALSE?
> in other words, can't we skip (include) the invalid page with a
> warning message?
>
> As I said before, I think that capturing more pages than expected
> will be better than not capturing a dump, and that is "robust"
> against unexpected values.

I chose failing to an recover attempt because i was not sure
that it won't have negative effects on other pages.
Your suggestion is replacing ERRMSG with a warning and then just
continue ? I can rework the patch.

Thanks
Regards
Alex

[PATCH v2 1/1] check that order of free pages falls within valid range

[HAGIO KAZUHITO =?unknown-8bit?b?6JCp5bC+IOS4gOS7gQ==?=]

-----Original Message-----
> 
> Hi Kazu,
> 
> HAGIO KAZUHITO(?????)	<k-hagio-ab@nec.com> writes:
> 
> > Hi Alex,
> >
> > thanks for the patch,
> >
> > -----Original Message-----
> >> Alexander Egorenkov <egorenar@linux.ibm.com> writes:
> >>
> >> > This change makes __exclude_unnecessary_pages() more robust by
> >> > verifying that the order of a free page is valid before computing the size
> >> > of its memory block in the buddy system.
> >> >
> >> > The order of a free page cannot be larger than (MAX_ORDER - 1) because
> >> > the array 'zone.free_area' is of size MAX_ORDER.
> >> >
> >> > This situation is reproducible with some s390x dumps:
> >> >
> >> > __exclude_unnecessary_pages: Invalid free page order: pfn=2690c0, order=52, max order=8
> >> >
> >> > References:
> >> > - https://listman.redhat.com/archives/crash-utility/2021-September/009204.html
> >> > - https://www.kernel.org/doc/gorman/html/understand/understand009.html
> >> >
> >> > Signed-off-by: Alexander Egorenkov <egorenar@linux.ibm.com>
> >> > ---
> >> >  makedumpfile.c | 6 ++++++
> >> >  1 file changed, 6 insertions(+)
> >> >
> >> > diff --git a/makedumpfile.c b/makedumpfile.c
> >> > index 2ef345879524..56aa026e7b34 100644
> >> > --- a/makedumpfile.c
> >> > +++ b/makedumpfile.c
> >> > @@ -6457,6 +6457,12 @@ __exclude_unnecessary_pages(unsigned long mem_map,
> >> >  		else if ((info->dump_level & DL_EXCLUDE_FREE)
> >> >  		    && info->page_is_buddy
> >> >  		    && info->page_is_buddy(flags, _mapcount, private, _count)) {
> >> > +			if (private >= ARRAY_LENGTH(zone.free_area)) {
> >> > +				ERRMSG("Invalid free page order: pfn=%llx, order=%lu, max order=%lu\n",
> >> > +				       pfn, private, ARRAY_LENGTH(zone.free_area) - 1);
> >> > +				free(page_cache);
> >> > +				return FALSE;
> >> > +			}
> >> >  			nr_pages = 1 << private;
> >> >  			pfn_counter = &pfn_free;
> >> >  		}
> >> > --
> >> > 2.34.1
> >> >
> >> >
> >> > _______________________________________________
> >> > kexec mailing list
> >> > kexec at lists.infradead.org
> >> > http://lists.infradead.org/mailman/listinfo/kexec
> >>
> >> I found out when this can happen.
> >>
> >> If e.g. a driver calls free_pages() and gives an order > max page order,
> >> then __free_one_page() stores the given invalid page order in the
> >> 'private' member of struct page and gives it back to the buddy
> >> allocator.
> >>
> >> This is what actually happened in the dump i used to reproduce this issue
> >> with makedumpfile.
> >
> > Good catch, though I could not reproduce it so far..
> >
> > but I wonder whether we have no other choice than returning FALSE?
> > in other words, can't we skip (include) the invalid page with a
> > warning message?
> >
> > As I said before, I think that capturing more pages than expected
> > will be better than not capturing a dump, and that is "robust"
> > against unexpected values.
> 
> I chose failing to an recover attempt because i was not sure
> that it won't have negative effects on other pages.

ah, I forgot but the issue was an infinite loop, so you chose failing
to avoid the same situation with negative effects on other pages, right?
I understand it.

hmm, but I think that it's too sensitive to stop makedumpfile with an
invalid value, it might be possible to complete dumping.  If it has
negative effects, let's fix it again.

> Your suggestion is replacing ERRMSG with a warning and then just
> continue ? I can rework the patch.

Yes, please.

Thanks,
Kazu