linux-hardening - Re: [PATCH 5/5] slab: Allocate and use per-call-site caches

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Message-ID: <202408221046.808356D202@keescook>
Date: Thu, 22 Aug 2024 10:47:36 -0700
From: Kees Cook <kees@...nel.org>
To: Xiu Jianfeng <xiujianfeng@...weicloud.com>
Cc: Vlastimil Babka <vbabka@...e.cz>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>,
	Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org,
	"GONG, Ruiqi" <gongruiqi@...weicloud.com>,
	Jann Horn <jannh@...gle.com>, Matteo Rizzo <matteorizzo@...gle.com>,
	jvoisin <julien.voisin@...tri.org>, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH 5/5] slab: Allocate and use per-call-site caches

On Sat, Aug 17, 2024 at 09:30:58AM +0800, Xiu Jianfeng wrote:
> Hi Kees,
> 
> On 2024/8/9 15:33, Kees Cook wrote:
> > Use separate per-call-site kmem_cache or kmem_buckets. These are
> > allocated on demand to avoid wasting memory for unused caches.
> > 
> > A few caches need to be allocated very early to support allocating the
> > caches themselves: kstrdup(), kvasprintf(), and pcpu_mem_zalloc(). Any
> > GFP_ATOMIC allocations are currently left to be allocated from
> > KMALLOC_NORMAL.
> > 
> > With a distro config, /proc/slabinfo grows from ~400 entries to ~2200.
> > 
> > Since this feature (CONFIG_SLAB_PER_SITE) is redundant to
> > CONFIG_RANDOM_KMALLOC_CACHES, mark it a incompatible. Add Kconfig help
> > text that compares the features.
> > 
> > Improvements needed:
> > - Retain call site gfp flags in alloc_tag meta field to:
> >   - pre-allocate all GFP_ATOMIC caches (since their caches cannot
> >     be allocated on demand unless we want them to be GFP_ATOMIC
> >     themselves...)
> >   - Separate MEMCG allocations as well
> > - Allocate individual caches within kmem_buckets on demand to
> >   further reduce memory usage overhead.
> > 
> > Signed-off-by: Kees Cook <kees@...nel.org>
> > ---
> > Cc: Suren Baghdasaryan <surenb@...gle.com>
> > Cc: Kent Overstreet <kent.overstreet@...ux.dev>
> > Cc: Vlastimil Babka <vbabka@...e.cz>
> > Cc: Christoph Lameter <cl@...ux.com>
> > Cc: Pekka Enberg <penberg@...nel.org>
> > Cc: David Rientjes <rientjes@...gle.com>
> > Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Roman Gushchin <roman.gushchin@...ux.dev>
> > Cc: Hyeonggon Yoo <42.hyeyoo@...il.com>
> > Cc: linux-mm@...ck.org
> > ---
> >  include/linux/alloc_tag.h |   8 +++
> >  lib/alloc_tag.c           | 121 +++++++++++++++++++++++++++++++++++---
> >  mm/Kconfig                |  19 +++++-
> >  mm/slab_common.c          |   1 +
> >  mm/slub.c                 |  31 +++++++++-
> >  5 files changed, 170 insertions(+), 10 deletions(-)
> > 
> 
> [...]
> 
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 3520acaf9afa..d14102c4b4d7 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -4135,6 +4135,35 @@ void *__kmalloc_large_node_noprof(size_t size, gfp_t flags, int node)
> >  }
> >  EXPORT_SYMBOL(__kmalloc_large_node_noprof);
> >  
> > +static __always_inline
> > +struct kmem_cache *choose_slab(size_t size, kmem_buckets *b, gfp_t flags,
> > +			       unsigned long caller)
> > +{
> > +#ifdef CONFIG_SLAB_PER_SITE
> > +	struct alloc_tag *tag = current->alloc_tag;
> 
> There is a compile error here if CONFIG_MEM_ALLOC_PROFILING is disabled
> when I test this patchset.
> 
> mm/slub.c: In function ‘choose_slab’:
> mm/slub.c:4187:40: error: ‘struct task_struct’ has no member named
> ‘alloc_tag’
>  4187 |         struct alloc_tag *tag = current->alloc_tag;
>       |                                        ^~
>   CC      mm/page_reporting.o
> 
> maybe CONFIG_SLAB_PER_SITE should depend on CONFIG_MEM_ALLOC_PROFILING

Thanks! I tried to make the Kconfig use the right dependencies, but I
clearly missed something. There is also some weird behavior between
"depends" and "select". I will get this fixed for the next version.

-Kees

-- 
Kees Cook