Linux Virtualization - Apr 2018 - [PATCH v3] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG

On Mon, Apr 23, 2018 at 08:06:16PM -0400, Mikulas Patocka
wrote:
> Some bugs (such as buffer overflows) are better detected
> with kmalloc code, so we must test the kmalloc path too.
Well now, this brings up another item for the collective TODO list --
implement redzone checks for vmalloc.  Unless this is something already
taken care of by kasan or similar.

On Mon, 23 Apr 2018, Matthew Wilcox wrote:
> On Mon, Apr 23, 2018 at 08:06:16PM -0400, Mikulas Patocka wrote:
> > Some bugs (such as buffer overflows) are better detected
> > with kmalloc code, so we must test the kmalloc path too.
> 
> Well now, this brings up another item for the collective TODO list --
> implement redzone checks for vmalloc.  Unless this is something already
> taken care of by kasan or similar.
The kmalloc overflow testing is also not ideal - it rounds the size up to 
the next slab size and detects buffer overflows only at this boundary.

Some times ago, I made a "kmalloc guard" patch that places a magic
number
immediatelly after the requested size - so that it can detect overflows at 
byte boundary 
( https://www.redhat.com/archives/dm-devel/2014-September/msg00018.html )

That patch found a bug in crypto code:
( http://lkml.iu.edu/hypermail/linux/kernel/1409.1/02325.html )

Mikulas

On Tue, Apr 24, 2018 at 08:29:14AM -0400, Mikulas Patocka
wrote:
> 
> 
> On Mon, 23 Apr 2018, Matthew Wilcox wrote:
> 
> > On Mon, Apr 23, 2018 at 08:06:16PM -0400, Mikulas Patocka wrote:
> > > Some bugs (such as buffer overflows) are better detected
> > > with kmalloc code, so we must test the kmalloc path too.
> > 
> > Well now, this brings up another item for the collective TODO list --
> > implement redzone checks for vmalloc.  Unless this is something
already
> > taken care of by kasan or similar.
> 
> The kmalloc overflow testing is also not ideal - it rounds the size up to 
> the next slab size and detects buffer overflows only at this boundary.
> 
> Some times ago, I made a "kmalloc guard" patch that places a
magic number
> immediatelly after the requested size - so that it can detect overflows at 
> byte boundary 
> ( https://www.redhat.com/archives/dm-devel/2014-September/msg00018.html )
> 
> That patch found a bug in crypto code:
> ( http://lkml.iu.edu/hypermail/linux/kernel/1409.1/02325.html )
Is it still worth doing this, now we have kasan?