KMSAN doesn't allow treating adjacent memory pages as such, if they were
allocated by different alloc_pages() calls.
The block layer however does so: adjacent pages end up being used
together. To prevent this, make page_is_mergeable() return false under
KMSAN.

Suggested-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>

---

v4:
 -- swap block: and kmsan: in the subject

Link: https://linux-review.googlesource.com/id/Ie29cc2464c70032347c32ab2a22e1e7a0b37b905
---
 block/bio.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/bio.c b/block/bio.c
index 51c99f2c5c908..ce6b3c82159a6 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -867,6 +867,8 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
 		return false;
 
 	*same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
+	if (!*same_page && IS_ENABLED(CONFIG_KMSAN))
+		return false;
 	if (*same_page)
 		return true;
 	return (bv->bv_page + bv_end / PAGE_SIZE) == (page + off / PAGE_SIZE);
-- 
2.37.0.rc0.161.g10f37bed90-goog

On Fri, Jul 01, 2022 at 04:22PM +0200, 'Alexander Potapenko' via kasan-dev wrote:
[...]
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -867,6 +867,8 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
>  		return false;
>  
>  	*same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
> +	if (!*same_page && IS_ENABLED(CONFIG_KMSAN))
> +		return false;
>  	if (*same_page)
>  		return true;

  	if (*same_page)
  		return true;
	else if (IS_ENABLED(CONFIG_KMSAN))
		return false;

>  	return (bv->bv_page + bv_end / PAGE_SIZE) == (page + off / PAGE_SIZE);

On Wed, Jul 13, 2022 at 12:23 PM Marco Elver <elver@google.com> wrote:
>
> On Fri, Jul 01, 2022 at 04:22PM +0200, 'Alexander Potapenko' via kasan-dev wrote:
> [...]
> > --- a/block/bio.c
> > +++ b/block/bio.c
> > @@ -867,6 +867,8 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
> >               return false;
> >
> >       *same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
> > +     if (!*same_page && IS_ENABLED(CONFIG_KMSAN))
> > +             return false;
> >       if (*same_page)
> >               return true;
>
>         if (*same_page)
>                 return true;
>         else if (IS_ENABLED(CONFIG_KMSAN))
>                 return false;
>
Done.
> >       return (bv->bv_page + bv_end / PAGE_SIZE) == (page + off / PAGE_SIZE);



-- 
Alexander Potapenko
Software Engineer

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