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Thu, 18 Jun 2020 20:05:59 +0000 Date: Thu, 18 Jun 2020 13:05:53 -0700 From: Roman Gushchin To: Vlastimil Babka CC: Kees Cook , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , , , , , Matthew Garrett , Jann Horn , Vijayanand Jitta Subject: Re: [PATCH 9/9] mm, slab/slub: move and improve cache_from_obj() Message-ID: <20200618200553.GE110603@carbon.dhcp.thefacebook.com> References: <20200610163135.17364-1-vbabka@suse.cz> <20200610163135.17364-10-vbabka@suse.cz> <202006171039.FBDF2D7F4A@keescook> Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: DM6PR13CA0017.namprd13.prod.outlook.com (2603:10b6:5:bc::30) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.dhcp.thefacebook.com (2620:10d:c090:400::5:632d) by DM6PR13CA0017.namprd13.prod.outlook.com (2603:10b6:5:bc::30) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3131.12 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 3361f039-3d84-4076-9de7-08d813c304e0 X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jun 2020 20:05:59.7024 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: CznfLt1AVUeqsTAYUDCBhzZBPFbHio5MlJVeYG+CmdmXvIYR7WhYUnqkeHOGyrg7 X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3399 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-06-18_15:2020-06-18,2020-06-18 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 phishscore=0 cotscore=-2147483648 malwarescore=0 adultscore=0 impostorscore=0 bulkscore=0 suspectscore=0 mlxscore=0 mlxlogscore=999 spamscore=0 clxscore=1015 priorityscore=1501 lowpriorityscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006180153 X-FB-Internal: deliver Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jun 18, 2020 at 12:10:38PM +0200, Vlastimil Babka wrote: > > On 6/17/20 7:49 PM, Kees Cook wrote: > > On Wed, Jun 10, 2020 at 06:31:35PM +0200, Vlastimil Babka wrote: > >> The function cache_from_obj() was added by commit b9ce5ef49f00 ("sl[au]b: > >> always get the cache from its page in kmem_cache_free()") to support kmemcg, > >> where per-memcg cache can be different from the root one, so we can't use > >> the kmem_cache pointer given to kmem_cache_free(). > >> > >> Prior to that commit, SLUB already had debugging check+warning that could be > >> enabled to compare the given kmem_cache pointer to one referenced by the slab > >> page where the object-to-be-freed resides. This check was moved to > >> cache_from_obj(). Later the check was also enabled for SLAB_FREELIST_HARDENED > >> configs by commit 598a0717a816 ("mm/slab: validate cache membership under > >> freelist hardening"). > >> > >> These checks and warnings can be useful especially for the debugging, which can > >> be improved. Commit 598a0717a816 changed the pr_err() with WARN_ON_ONCE() to > >> WARN_ONCE() so only the first hit is now reported, others are silent. This > >> patch changes it to WARN() so that all errors are reported. > >> > >> It's also useful to print SLUB allocation/free tracking info for the offending > >> object, if tracking is enabled. We could export the SLUB print_tracking() > >> function and provide an empty one for SLAB, or realize that both the debugging > >> and hardening cases in cache_from_obj() are only supported by SLUB anyway. So > >> this patch moves cache_from_obj() from slab.h to separate instances in slab.c > >> and slub.c, where the SLAB version only does the kmemcg lookup and even could > > > > Oops. I made a mistake when I applied CONFIG_SLAB_FREELIST_HARDENED > > here, I was thinking of SLAB_FREELIST_RANDOM's coverage (SLUB and SLAB), > > and I see now that I never updated CONFIG_SLAB_FREELIST_HARDENED to > > cover SLAB and SLOB. > > > > The point being: I still want the sanity check for the SLAB case under > > hardening. This needs to stay a common function. The whole point is > > to catch corruption from the wrong kmem_cache * being associated with > > an object, and that's agnostic of slab/slub/slob. > > > > So, I'll send a follow-up to this patch to actually do what I had > > originally intended for 598a0717a816 ("mm/slab: validate cache membership > > under freelist hardening"), which wasn't intended to be SLUB-specific. > > To prvent the churn of your patch moving the cache_from_obj() back to slab.h, I > think it's best if we modify my patch. The patch below should be squashed into > the current version in mmots, with the commit log used for the whole result. > > This will cause conflicts while reapplying Roman's > mm-memcg-slab-use-a-single-set-of-kmem_caches-for-all-allocations.patch which > can be fixed by > a) throwing away the conflicting hunks for cache_from_obj() in slab.c and slub.c > b) applying this hunk instead: > > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -455,12 +455,11 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x) > struct kmem_cache *cachep; > > if (!IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && > - !memcg_kmem_enabled() && > !kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS)) > return s; > > cachep = virt_to_cache(x); > - if (WARN(cachep && !slab_equal_or_root(cachep, s), > + if (WARN(cachep && cachep != s, > "%s: Wrong slab cache. %s but object is from %s\n", > __func__, s->name, cachep->name)) > print_tracking(cachep, x); > > The fixup patch itself: > ----8<---- > From b8df607d92b37e5329ce7bda62b2b364cc249893 Mon Sep 17 00:00:00 2001 > From: Vlastimil Babka > Date: Thu, 18 Jun 2020 11:52:03 +0200 > Subject: [PATCH] mm, slab/slub: improve error reporting and overhead of > cache_from_obj() > > The function cache_from_obj() was added by commit b9ce5ef49f00 ("sl[au]b: > always get the cache from its page in kmem_cache_free()") to support > kmemcg, where per-memcg cache can be different from the root one, so we > can't use the kmem_cache pointer given to kmem_cache_free(). > > Prior to that commit, SLUB already had debugging check+warning that could > be enabled to compare the given kmem_cache pointer to one referenced by > the slab page where the object-to-be-freed resides. This check was moved > to cache_from_obj(). Later the check was also enabled for > SLAB_FREELIST_HARDENED configs by commit 598a0717a816 ("mm/slab: validate > cache membership under freelist hardening"). > > These checks and warnings can be useful especially for the debugging, > which can be improved. Commit 598a0717a816 changed the pr_err() with > WARN_ON_ONCE() to WARN_ONCE() so only the first hit is now reported, > others are silent. This patch changes it to WARN() so that all errors are > reported. > > It's also useful to print SLUB allocation/free tracking info for the offending > object, if tracking is enabled. Thus, export the SLUB print_tracking() function > and provide an empty one for SLAB. > > For SLUB we can also benefit from the static key check in > kmem_cache_debug_flags(), but we need to move this function to slab.h and > declare the static key there. > > [1] https://lore.kernel.org/r/20200608230654.828134-18-guro@fb.com > > Signed-off-by: Vlastimil Babka Acked-by: Roman Gushchin Thanks! > --- > mm/slab.c | 8 -------- > mm/slab.h | 45 +++++++++++++++++++++++++++++++++++++++++++++ > mm/slub.c | 38 +------------------------------------- > 3 files changed, 46 insertions(+), 45 deletions(-) > > diff --git a/mm/slab.c b/mm/slab.c > index 6134c4c36d4c..9350062ffc1a 100644 > --- a/mm/slab.c > +++ b/mm/slab.c > @@ -3672,14 +3672,6 @@ void *__kmalloc_track_caller(size_t size, gfp_t flags, unsigned long caller) > } > EXPORT_SYMBOL(__kmalloc_track_caller); > > -static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x) > -{ > - if (memcg_kmem_enabled()) > - return virt_to_cache(x); > - else > - return s; > -} > - > /** > * kmem_cache_free - Deallocate an object > * @cachep: The cache the allocation was from. > diff --git a/mm/slab.h b/mm/slab.h > index a2696d306b62..a9f5ba9ce9a7 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -275,6 +275,34 @@ static inline int cache_vmstat_idx(struct kmem_cache *s) > NR_SLAB_RECLAIMABLE : NR_SLAB_UNRECLAIMABLE; > } > > +#ifdef CONFIG_SLUB_DEBUG > +#ifdef CONFIG_SLUB_DEBUG_ON > +DECLARE_STATIC_KEY_TRUE(slub_debug_enabled); > +#else > +DECLARE_STATIC_KEY_FALSE(slub_debug_enabled); > +#endif > +extern void print_tracking(struct kmem_cache *s, void *object); > +#else > +static inline void print_tracking(struct kmem_cache *s, void *object) > +{ > +} > +#endif > + > +/* > + * Returns true if any of the specified slub_debug flags is enabled for the > + * cache. Use only for flags parsed by setup_slub_debug() as it also enables > + * the static key. > + */ > +static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t flags) > +{ > + VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS)); > +#ifdef CONFIG_SLUB_DEBUG > + if (static_branch_unlikely(&slub_debug_enabled)) > + return s->flags & flags; > +#endif > + return false; > +} > + > #ifdef CONFIG_MEMCG_KMEM > > /* List of all root caches. */ > @@ -503,6 +531,23 @@ static __always_inline void uncharge_slab_page(struct page *page, int order, > memcg_uncharge_slab(page, order, s); > } > > +static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x) > +{ > + struct kmem_cache *cachep; > + > + if (!IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && > + !memcg_kmem_enabled() && > + !kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS)) > + return s; > + > + cachep = virt_to_cache(x); > + if (WARN(cachep && !slab_equal_or_root(cachep, s), > + "%s: Wrong slab cache. %s but object is from %s\n", > + __func__, s->name, cachep->name)) > + print_tracking(cachep, x); > + return cachep; > +} > + > static inline size_t slab_ksize(const struct kmem_cache *s) > { > #ifndef CONFIG_SLUB > diff --git a/mm/slub.c b/mm/slub.c > index 202fb423d195..0e635a8aa340 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -122,21 +122,6 @@ DEFINE_STATIC_KEY_FALSE(slub_debug_enabled); > #endif > #endif > > -/* > - * Returns true if any of the specified slub_debug flags is enabled for the > - * cache. Use only for flags parsed by setup_slub_debug() as it also enables > - * the static key. > - */ > -static inline bool kmem_cache_debug_flags(struct kmem_cache *s, slab_flags_t flags) > -{ > - VM_WARN_ON_ONCE(!(flags & SLAB_DEBUG_FLAGS)); > -#ifdef CONFIG_SLUB_DEBUG > - if (static_branch_unlikely(&slub_debug_enabled)) > - return s->flags & flags; > -#endif > - return false; > -} > - > static inline bool kmem_cache_debug(struct kmem_cache *s) > { > return kmem_cache_debug_flags(s, SLAB_DEBUG_FLAGS); > @@ -653,7 +638,7 @@ static void print_track(const char *s, struct track *t, unsigned long pr_time) > #endif > } > > -static void print_tracking(struct kmem_cache *s, void *object) > +void print_tracking(struct kmem_cache *s, void *object) > { > unsigned long pr_time = jiffies; > if (!(s->flags & SLAB_STORE_USER)) > @@ -1525,10 +1510,6 @@ static bool freelist_corrupted(struct kmem_cache *s, struct page *page, > { > return false; > } > - > -static void print_tracking(struct kmem_cache *s, void *object) > -{ > -} > #endif /* CONFIG_SLUB_DEBUG */ > > /* > @@ -3180,23 +3161,6 @@ void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr) > } > #endif > > -static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x) > -{ > - struct kmem_cache *cachep; > - > - if (!IS_ENABLED(CONFIG_SLAB_FREELIST_HARDENED) && > - !memcg_kmem_enabled() && > - !kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS)) > - return s; > - > - cachep = virt_to_cache(x); > - if (WARN(cachep && !slab_equal_or_root(cachep, s), > - "%s: Wrong slab cache. %s but object is from %s\n", > - __func__, s->name, cachep->name)) > - print_tracking(cachep, x); > - return cachep; > -} > - > void kmem_cache_free(struct kmem_cache *s, void *x) > { > s = cache_from_obj(s, x); > -- > 2.27.0 > >