Re: [PATCH v6 00/37] Memory allocation profiling

Kees Cook
2024-04-25T20:00:56Z

On Thu, Apr 25, 2024 at 08:39:37AM -0700, Suren Baghdasaryan wrote:
> On Wed, Apr 24, 2024 at 8:26 PM Kent Overstreet
> <kent.overstreet@linux.dev> wrote:
> >
> > On Wed, Apr 24, 2024 at 06:59:01PM -0700, Kees Cook wrote:
> > > On Thu, Mar 21, 2024 at 09:36:22AM -0700, Suren Baghdasaryan wrote:
> > > > Low overhead [1] per-callsite memory allocation profiling. Not just for
> > > > debug kernels, overhead low enough to be deployed in production.
> > >
> > > Okay, I think I'm holding it wrong. With next-20240424 if I set:
> > >
> > > CONFIG_CODE_TAGGING=y
> > > CONFIG_MEM_ALLOC_PROFILING=y
> > > CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT=y
> > >
> > > My test system totally freaks out:
> > >
> > > ...
> > > SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
> > > Oops: general protection fault, probably for non-canonical address 0xc388d881e4808550: 0000 [#1] PREEMPT SMP NOPTI
> > > CPU: 0 PID: 0 Comm: swapper Not tainted 6.9.0-rc5-next-20240424 #1
> > > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
> > > RIP: 0010:__kmalloc_node_noprof+0xcd/0x560
> > >
> > > Which is:
> > >
> > > __kmalloc_node_noprof+0xcd/0x560:
> > > __slab_alloc_node at mm/slub.c:3780 (discriminator 2)
> > > (inlined by) slab_alloc_node at mm/slub.c:3982 (discriminator 2)
> > > (inlined by) __do_kmalloc_node at mm/slub.c:4114 (discriminator 2)
> > > (inlined by) __kmalloc_node_noprof at mm/slub.c:4122 (discriminator 2)
> > >
> > > Which is:
> > >
> > > tid = READ_ONCE(c->tid);
> > >
> > > I haven't gotten any further than that; I'm EOD. Anyone seen anything
> > > like this with this series?
> >
> > I certainly haven't. That looks like some real corruption, we're in slub
> > internal data structures and derefing a garbage address. Check kasan and
> > all that?
>
> Hi Kees,
> I tested next-20240424 yesterday with defconfig and
> CONFIG_MEM_ALLOC_PROFILING enabled but didn't see any issue like that.
> Could you share your config file please?

Well *that* took a while to .config bisect. I probably should have found
it sooner, but CONFIG_DEBUG_KMEMLEAK=y is what broke me. Without that,
everything is lovely! :)

I can reproduce it now with:

$ make defconfig kvm_guest.config
$ ./scripts/config -e CONFIG_MEM_ALLOC_PROFILING -e CONFIG_DEBUG_KMEMLEAK

-Kees

--
Kees Cook