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Date: Tue, 15 May 2018 10:13:11 +0900 From: Joonsoo Kim <iamjoonsoo.kim@....com> To: Mikulas Patocka <mpatocka@...hat.com> Cc: Matthew Wilcox <willy@...radead.org>, Michal Hocko <mhocko@...nel.org>, David Miller <davem@...emloft.net>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, eric.dumazet@...il.com, edumazet@...gle.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, mst@...hat.com, jasowang@...hat.com, virtualization@...ts.linux-foundation.org, dm-devel@...hat.com, Vlastimil Babka <vbabka@...e.cz>, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com> Subject: Re: [PATCH v3] kvmalloc: always use vmalloc if CONFIG_DEBUG_SG Hello, Mikulas. On Tue, Apr 24, 2018 at 02:41:47PM -0400, Mikulas Patocka wrote: > > > 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. I skimm at your code and it requires rebuilding the kernel. I think that if rebuilding is required as the same with the KASAN, using the KASAN is better since it has far better coverage for detection the bug. However, I think that if the redzone can be setup tightly without rebuild, it would be worth implementing. I have an idea to implement it only for the SLUB. Could I try it? (I'm asking this because I'm inspired from the above patch.) :) Or do you wanna try it? Thanks.
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