| Message ID | 20190125173827.2658-1-willy@infradead.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm: Prevent mapping slab pages to userspace | expand |
On Sat, Jan 26, 2019 at 6:38 AM Matthew Wilcox <willy@infradead.org> wrote: > > It's never appropriate to map a page allocated by SLAB into userspace. > A buggy device driver might try this, or an attacker might be able to > find a way to make it happen. > > Signed-off-by: Matthew Wilcox <willy@infradead.org> > --- > mm/memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index e11ca9dd823f..ce8c90b752be 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1451,7 +1451,7 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr, > spinlock_t *ptl; > > retval = -EINVAL; > - if (PageAnon(page)) > + if (PageAnon(page) || PageSlab(page)) Are there other types that should not get mapped? (Or better yet, is there a whitelist of those that are okay to be mapped?) Either way, this sounds good. :) Reviewed-by: Kees Cook <keescook@chromium.org> -Kees > goto out; > retval = -ENOMEM; > flush_dcache_page(page); > -- > 2.20.1 >
On Sat, Jan 26, 2019 at 07:44:40AM +1300, Kees Cook wrote: > > - if (PageAnon(page)) > > + if (PageAnon(page) || PageSlab(page)) > > Are there other types that should not get mapped? (Or better yet, is > there a whitelist of those that are okay to be mapped?) Funny you should ask; I think the next patch in this series looks like this: - if (PageAnon(page) || PageSlab(page)) + if (PageAnon(page) || PageSlab(page) || page_has_type(page)) but let's see if there's something I've overlooked with this patch.
On Fri, 25 Jan 2019 09:38:27 -0800 Matthew Wilcox <willy@infradead.org> wrote: > It's never appropriate to map a page allocated by SLAB into userspace. > A buggy device driver might try this, or an attacker might be able to > find a way to make it happen. It wouldn't surprise me if someone somewhere is doing this. Rather than mysteriously breaking their code, how about we emit a warning and still permit it to proceed, for a while?
On Tue, Jan 29, 2019 at 7:21 AM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Fri, 25 Jan 2019 09:38:27 -0800 Matthew Wilcox <willy@infradead.org> wrote: > > > It's never appropriate to map a page allocated by SLAB into userspace. > > A buggy device driver might try this, or an attacker might be able to > > find a way to make it happen. > > It wouldn't surprise me if someone somewhere is doing this. Rather > than mysteriously breaking their code, how about we emit a warning and > still permit it to proceed, for a while? It seems like a fatal condition to me? There's nothing to check that such a page wouldn't get freed by the slab while still mapped to userspace, right? But I'll take warning over not checking. :)
On Tue, 29 Jan 2019, Kees Cook wrote: > It seems like a fatal condition to me? There's nothing to check that > such a page wouldn't get freed by the slab while still mapped to > userspace, right? Lets just fail the code. Currently this may work with SLUB. But SLAB and SLOB overlay fields with mapcount. So you would have a corrupted page struct if you mapped a slab page to user space.
Matthew Wilcox <willy@infradead.org> writes: > It's never appropriate to map a page allocated by SLAB into userspace. > A buggy device driver might try this, or an attacker might be able to > find a way to make it happen. > > Signed-off-by: Matthew Wilcox <willy@infradead.org> > --- > mm/memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index e11ca9dd823f..ce8c90b752be 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1451,7 +1451,7 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr, > spinlock_t *ptl; > > retval = -EINVAL; > - if (PageAnon(page)) > + if (PageAnon(page) || PageSlab(page)) > goto out; > retval = -ENOMEM; > flush_dcache_page(page); Thanks for turning this into an actual patch. cheers
On 25/01/2019 19.38, Matthew Wilcox wrote: > It's never appropriate to map a page allocated by SLAB into userspace. > A buggy device driver might try this, or an attacker might be able to > find a way to make it happen. > > Signed-off-by: Matthew Wilcox <willy@infradead.org> Acked-by: Pekka Enberg <penberg@kernel.org> A WARN_ON_ONCE() would be nice here to let those buggy drivers know that they will no longer work. > --- > mm/memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index e11ca9dd823f..ce8c90b752be 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1451,7 +1451,7 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr, > spinlock_t *ptl; > > retval = -EINVAL; > - if (PageAnon(page)) > + if (PageAnon(page) || PageSlab(page)) > goto out; > retval = -ENOMEM; > flush_dcache_page(page); >
diff --git a/mm/memory.c b/mm/memory.c index e11ca9dd823f..ce8c90b752be 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1451,7 +1451,7 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr, spinlock_t *ptl; retval = -EINVAL; - if (PageAnon(page)) + if (PageAnon(page) || PageSlab(page)) goto out; retval = -ENOMEM; flush_dcache_page(page);
It's never appropriate to map a page allocated by SLAB into userspace. A buggy device driver might try this, or an attacker might be able to find a way to make it happen. Signed-off-by: Matthew Wilcox <willy@infradead.org> --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)