Re: [PATCH v3] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG
From: Mikulas Patocka
Date: Tue Apr 24 2018 - 14:41:57 EST
On Tue, 24 Apr 2018, Matthew Wilcox wrote:
> 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?
The kmalloc guard has much lower overhead than kasan.
(BTW. when I tried kasan, it oopsed with persistent memory)