From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-14.4 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_IN_DEF_DKIM_WL autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D208DC433DF for ; Wed, 20 May 2020 04:45:14 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 6F4512075F for ; Wed, 20 May 2020 04:45:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="IksOG6lq" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F4512075F Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D47438004C; Wed, 20 May 2020 00:45:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CF8188002C; Wed, 20 May 2020 00:45:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C0DCC8004C; Wed, 20 May 2020 00:45:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0165.hostedemail.com [216.40.44.165]) by kanga.kvack.org (Postfix) with ESMTP id AA4E98002C for ; Wed, 20 May 2020 00:45:13 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 6E942824805A for ; Wed, 20 May 2020 04:45:13 +0000 (UTC) X-FDA: 76835858106.28.shoe85_84da359dd932d X-HE-Tag: shoe85_84da359dd932d X-Filterd-Recvd-Size: 16195 Received: from mail-qv1-f67.google.com (mail-qv1-f67.google.com [209.85.219.67]) by imf35.hostedemail.com (Postfix) with ESMTP for ; Wed, 20 May 2020 04:45:12 +0000 (UTC) Received: by mail-qv1-f67.google.com with SMTP id x13so774780qvr.2 for ; Tue, 19 May 2020 21:45:12 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=SNby9Ybh2Qrd4287Y3ZzbQLjxz1GHTGW0zNl9NdTkP0=; b=IksOG6lqm3kxNh7uPbJz8mL/02gwoLveO2rUXhNLb950S584/AWZ8lopuGUFPJuWsM Xa8/knGXPAI5S9yLJnkMnDS+0M2PGSERtmlhh5Vkx4+aMdTAUQsAwIFHKe6XgfrmJLN2 +HRxXQuHjLeq6DNH/8VesQgUOwMWBgakWYuhhob0ZEMnZbZGWliBOBau/jLhMc5NXF19 zT5N0Y7TQUdk4Fu0OEM+PYoTZdxA+PWAyozjisUPmA9iEk06hhhXJG+etiOTGEjvegmu MVdrGShTbqqhWpqDwgtRLrKR19OUJc/OTdK3YEWM5ykam6MQmnVAfo1IDAiNNMtQ3oE+ ZSjw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=SNby9Ybh2Qrd4287Y3ZzbQLjxz1GHTGW0zNl9NdTkP0=; b=WAhN1w50zHPZrKWG2qwANHMJWUn6f0wavmebkQG/7M1rUV+dkAoXDu8zHN7hv1+KGA nl5RrcL80Ij1majpfUTV9tK1Pqqi4jCn7GKlcpn7IO9rQymtBLzTf1He8/s7As9GrV/2 ymMS5VFsc7RijHkwtwY+iMdnUi1wKI7IBNxD55Rlu1zJ96CssbanB/4HHZIQGr2B4uOP RA+V28iWIZUBp0Co9/UWl1TIYHONQZlsLCFC3yRjGHubB+Q0JymMVNEhgViaR9ByA8Po Rr/NKos/pPtVQ4UBQ9r8u1X4f9bUXSbHcA0MuIxuuWTmSxxgBvhKGVelbzzAIsewQcrk 0rKQ== X-Gm-Message-State: AOAM533ONhwLNIBdNR2mvrBay1EIsQ2Zkf4lB/slHV3F5BW4ZlJZTmz1 xWnlLP9juiXiBIDFkPFVglbiJV9dgvxr35WooyTZa6Uu9aU= X-Google-Smtp-Source: ABdhPJzcgfZnMxpvonX+fPxLM4xpBpLm8XlltEuajLADGFv3ZFOj8evWjq6+N6YWZxgf/DG5sL+RGRNz7I8Mq5yfcgc= X-Received: by 2002:a0c:db03:: with SMTP id d3mr3196334qvk.80.1589949911824; Tue, 19 May 2020 21:45:11 -0700 (PDT) MIME-Version: 1.0 References: <20200519022517.24182-1-walter-zh.wu@mediatek.com> <1589947387.29577.35.camel@mtksdccf07> In-Reply-To: <1589947387.29577.35.camel@mtksdccf07> From: Dmitry Vyukov Date: Wed, 20 May 2020 06:45:00 +0200 Message-ID: Subject: Re: [PATCH v4 2/4] kasan: record and print the free track To: Walter Wu Cc: Andrey Ryabinin , Alexander Potapenko , kasan-dev , Linux-MM , LKML , Linux ARM , wsd_upstream , linux-mediatek@lists.infradead.org Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 20, 2020 at 6:03 AM Walter Wu wrote: > > > On Tue, May 19, 2020 at 4:25 AM Walter Wu wrote: > > > > > > Move free track from slub alloc meta-data to slub free meta-data in > > > order to make struct kasan_free_meta size is 16 bytes. It is a good > > > size because it is the minimal redzone size and a good number of > > > alignment. > > > > > > For free track in generic KASAN, we do the modification in struct > > > kasan_alloc_meta and kasan_free_meta: > > > - remove free track from kasan_alloc_meta. > > > - add free track into kasan_free_meta. > > > > > > [1]https://bugzilla.kernel.org/show_bug.cgi?id=198437 > > > > > > Signed-off-by: Walter Wu > > > Suggested-by: Dmitry Vyukov > > > Cc: Andrey Ryabinin > > > Cc: Dmitry Vyukov > > > Cc: Alexander Potapenko > > > --- > > > mm/kasan/common.c | 22 ++-------------------- > > > mm/kasan/generic.c | 18 ++++++++++++++++++ > > > mm/kasan/kasan.h | 7 +++++++ > > > mm/kasan/report.c | 20 -------------------- > > > mm/kasan/tags.c | 37 +++++++++++++++++++++++++++++++++++++ > > > 5 files changed, 64 insertions(+), 40 deletions(-) > > > > > > diff --git a/mm/kasan/common.c b/mm/kasan/common.c > > > index 8bc618289bb1..47b53912f322 100644 > > > --- a/mm/kasan/common.c > > > +++ b/mm/kasan/common.c > > > @@ -51,7 +51,7 @@ depot_stack_handle_t kasan_save_stack(gfp_t flags) > > > return stack_depot_save(entries, nr_entries, flags); > > > } > > > > > > -static inline void set_track(struct kasan_track *track, gfp_t flags) > > > +void kasan_set_track(struct kasan_track *track, gfp_t flags) > > > { > > > track->pid = current->pid; > > > track->stack = kasan_save_stack(flags); > > > @@ -299,24 +299,6 @@ struct kasan_free_meta *get_free_info(struct kmem_cache *cache, > > > return (void *)object + cache->kasan_info.free_meta_offset; > > > } > > > > > > - > > > -static void kasan_set_free_info(struct kmem_cache *cache, > > > - void *object, u8 tag) > > > -{ > > > - struct kasan_alloc_meta *alloc_meta; > > > - u8 idx = 0; > > > - > > > - alloc_meta = get_alloc_info(cache, object); > > > - > > > -#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY > > > - idx = alloc_meta->free_track_idx; > > > - alloc_meta->free_pointer_tag[idx] = tag; > > > - alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS; > > > -#endif > > > - > > > - set_track(&alloc_meta->free_track[idx], GFP_NOWAIT); > > > -} > > > - > > > void kasan_poison_slab(struct page *page) > > > { > > > unsigned long i; > > > @@ -492,7 +474,7 @@ static void *__kasan_kmalloc(struct kmem_cache *cache, const void *object, > > > KASAN_KMALLOC_REDZONE); > > > > > > if (cache->flags & SLAB_KASAN) > > > - set_track(&get_alloc_info(cache, object)->alloc_track, flags); > > > + kasan_set_track(&get_alloc_info(cache, object)->alloc_track, flags); > > > > > > return set_tag(object, tag); > > > } > > > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c > > > index 3372bdcaf92a..763d8a13e0ac 100644 > > > --- a/mm/kasan/generic.c > > > +++ b/mm/kasan/generic.c > > > @@ -344,3 +344,21 @@ void kasan_record_aux_stack(void *addr) > > > alloc_info->aux_stack[1] = alloc_info->aux_stack[0]; > > > alloc_info->aux_stack[0] = kasan_save_stack(GFP_NOWAIT); > > > } > > > + > > > +void kasan_set_free_info(struct kmem_cache *cache, > > > + void *object, u8 tag) > > > +{ > > > + struct kasan_free_meta *free_meta; > > > + > > > + free_meta = get_free_info(cache, object); > > > + kasan_set_track(&free_meta->free_track, GFP_NOWAIT); > > > +} > > > + > > > +struct kasan_track *kasan_get_free_track(struct kmem_cache *cache, > > > + void *object, u8 tag) > > > +{ > > > + struct kasan_free_meta *free_meta; > > > + > > > + free_meta = get_free_info(cache, object); > > > + return &free_meta->free_track; > > > +} > > > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h > > > index a7391bc83070..ad897ec36545 100644 > > > --- a/mm/kasan/kasan.h > > > +++ b/mm/kasan/kasan.h > > > @@ -127,6 +127,9 @@ struct kasan_free_meta { > > > * Otherwise it might be used for the allocator freelist. > > > */ > > > struct qlist_node quarantine_link; > > > +#ifdef CONFIG_KASAN_GENERIC > > > + struct kasan_track free_track; > > > +#endif > > > }; > > > > > > struct kasan_alloc_meta *get_alloc_info(struct kmem_cache *cache, > > > @@ -168,6 +171,10 @@ void kasan_report_invalid_free(void *object, unsigned long ip); > > > struct page *kasan_addr_to_page(const void *addr); > > > > > > depot_stack_handle_t kasan_save_stack(gfp_t flags); > > > +void kasan_set_track(struct kasan_track *track, gfp_t flags); > > > +void kasan_set_free_info(struct kmem_cache *cache, void *object, u8 tag); > > > +struct kasan_track *kasan_get_free_track(struct kmem_cache *cache, > > > + void *object, u8 tag); > > > > > > #if defined(CONFIG_KASAN_GENERIC) && \ > > > (defined(CONFIG_SLAB) || defined(CONFIG_SLUB)) > > > diff --git a/mm/kasan/report.c b/mm/kasan/report.c > > > index 6f8f2bf8f53b..96d2657fe70f 100644 > > > --- a/mm/kasan/report.c > > > +++ b/mm/kasan/report.c > > > @@ -159,26 +159,6 @@ static void describe_object_addr(struct kmem_cache *cache, void *object, > > > (void *)(object_addr + cache->object_size)); > > > } > > > > > > -static struct kasan_track *kasan_get_free_track(struct kmem_cache *cache, > > > - void *object, u8 tag) > > > -{ > > > - struct kasan_alloc_meta *alloc_meta; > > > - int i = 0; > > > - > > > - alloc_meta = get_alloc_info(cache, object); > > > - > > > -#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY > > > - for (i = 0; i < KASAN_NR_FREE_STACKS; i++) { > > > - if (alloc_meta->free_pointer_tag[i] == tag) > > > - break; > > > - } > > > - if (i == KASAN_NR_FREE_STACKS) > > > - i = alloc_meta->free_track_idx; > > > -#endif > > > - > > > - return &alloc_meta->free_track[i]; > > > -} > > > - > > > #ifdef CONFIG_KASAN_GENERIC > > > static void print_stack(depot_stack_handle_t stack) > > > { > > > diff --git a/mm/kasan/tags.c b/mm/kasan/tags.c > > > index 25b7734e7013..201dee5d6ae0 100644 > > > --- a/mm/kasan/tags.c > > > +++ b/mm/kasan/tags.c > > > @@ -162,3 +162,40 @@ void __hwasan_tag_memory(unsigned long addr, u8 tag, unsigned long size) > > > kasan_poison_shadow((void *)addr, size, tag); > > > } > > > EXPORT_SYMBOL(__hwasan_tag_memory); > > > + > > > +void kasan_set_free_info(struct kmem_cache *cache, > > > + void *object, u8 tag) > > > +{ > > > + struct kasan_alloc_meta *alloc_meta; > > > + u8 idx = 0; > > > + > > > + alloc_meta = get_alloc_info(cache, object); > > > + > > > +#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY > > > + idx = alloc_meta->free_track_idx; > > > + alloc_meta->free_pointer_tag[idx] = tag; > > > + alloc_meta->free_track_idx = (idx + 1) % KASAN_NR_FREE_STACKS; > > > +#endif > > > + > > > + kasan_set_track(&alloc_meta->free_track[idx], GFP_NOWAIT); > > > +} > > > + > > > +struct kasan_track *kasan_get_free_track(struct kmem_cache *cache, > > > + void *object, u8 tag) > > > +{ > > > + struct kasan_alloc_meta *alloc_meta; > > > + int i = 0; > > > + > > > + alloc_meta = get_alloc_info(cache, object); > > > + > > > +#ifdef CONFIG_KASAN_SW_TAGS_IDENTIFY > > > + for (i = 0; i < KASAN_NR_FREE_STACKS; i++) { > > > + if (alloc_meta->free_pointer_tag[i] == tag) > > > + break; > > > + } > > > + if (i == KASAN_NR_FREE_STACKS) > > > + i = alloc_meta->free_track_idx; > > > +#endif > > > + > > > + return &alloc_meta->free_track[i]; > > > +} > > > > Hi Walter, > > > > FTR I've uploaded this for review purposes here: > > https://linux-review.googlesource.com/c/linux/kernel/git/torvalds/linux/+/2458 > > > > Diff from the previous version is available as: > > https://linux-review.googlesource.com/c/linux/kernel/git/torvalds/linux/+/2458/1..2 > > > > I've tested this locally and with syzkaller. This is : > > > > [ 80.583021][ C3] Freed by task 0: > > [ 80.583480][ C3] kasan_save_stack+0x1b/0x40 mm/kasan/common.c:49 > > [ 80.584056][ C3] kasan_set_track+0x1c/0x30 mm/kasan/common.c:57 > > [ 80.584617][ C3] kasan_set_free_info+0x1b/0x30 mm/kasan/generic.c:354 > > [ 80.585221][ C3] __kasan_slab_free+0xd8/0x120 mm/kasan/common.c:438 > > [ 80.585814][ C3] __cache_free mm/slab.c:3426 [inline] > > [ 80.585814][ C3] kfree+0x10b/0x2b0 mm/slab.c:3757 > > [ 80.586291][ C3] kasan_rcu_reclaim+0x16/0x43 [test_kasan] > > [ 80.587009][ C3] rcu_do_batch kernel/rcu/tree.c:2207 [inline] > > [ 80.587009][ C3] rcu_core+0x59f/0x1370 kernel/rcu/tree.c:2434 > > [ 80.587537][ C3] __do_softirq+0x26c/0x9fa kernel/softirq.c:292 > > [ 80.588085][ C3] > > [ 80.588367][ C3] Last one call_rcu() call stack: > > [ 80.589052][ C3] kasan_save_stack+0x1b/0x40 mm/kasan/common.c:49 > > [ 80.589622][ C3] kasan_record_aux_stack+0x82/0xb0 mm/kasan/generic.c:345 > > [ 80.590254][ C3] __call_rcu kernel/rcu/tree.c:2672 [inline] > > [ 80.590254][ C3] call_rcu+0x14f/0x7f0 kernel/rcu/tree.c:2746 > > [ 80.590782][ C3] kasan_rcu_uaf+0xe4/0xeb [test_kasan] > > [ 80.591697][ C3] kmalloc_tests_init+0xbc/0x1097 [test_kasan] > > [ 80.592900][ C3] do_one_initcall+0x10a/0x7d0 init/main.c:1196 > > [ 80.593494][ C3] do_init_module+0x1e6/0x6d0 kernel/module.c:3539 > > [ 80.594066][ C3] load_module+0x7464/0x9450 kernel/module.c:3890 > > [ 80.594626][ C3] __do_sys_init_module+0x1e3/0x220 kernel/module.c:3953 > > [ 80.595265][ C3] do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295 > > [ 80.595822][ C3] entry_SYSCALL_64_after_hwframe+0x49/0xb3 > > > > > > Overall this looks very good to me. > > But there is one aspect that bothers me. In the previous patch you had > > code that returned NULL from kasan_get_free_track() if the object is > > live (which means free meta is not available, it's occupied by object > > data). Now you dropped that code, but I think we still need it. > > Otherwise we cast user object data to free meta and print the free > > stack/pid from whatever garbage is there. This may lead to very > > confusing output and potentially to crashes in stackdepot. > > > > Yes, I totally agree with you. In the previous email I thought that > there is a problem with free track, but I did not point it out. Thank > you for pointing this problem. As you mentioned, we should fix it. > > > What do you think about this patch on top of your patches? > > https://linux-review.googlesource.com/c/linux/kernel/git/torvalds/linux/+/2478 > > This way we very precisely mark the period of time when the object has > > free track live and set. > > If it looks good to you, feel free to incorporate it into your series. > > > > Thank you for providing good idea solution. > > I saw this patch, that is a great patch. I think it can fix the issue > which has garbage stack. it should work as described below. > > 1). When object is live, then don't print free stack. > 2). When object is NOT alive, after free object: > 2a). when object is in quarantine, then it can print free stack > 2b). when object is NOT in quarantine, then it can NOT print free stack. > > I have a question about 2), why we don't directly use > KASAN_KMALLOC_FREE? if we directly use it, then 2b) can print free > stack? 2b) may has use-after-free? so that it may need free stack. We can't use KASAN_KMALLOC_FREE because of this part: static bool __kasan_slab_free(struct kmem_cache *cache, void *object, unsigned long ip, bool quarantine) { ... kasan_poison_shadow(object, rounded_up_size, KASAN_KMALLOC_FREE); if ((IS_ENABLED(CONFIG_KASAN_GENERIC) && !quarantine) || unlikely(!(cache->flags & SLAB_KASAN))) return false; kasan_set_free_info(cache, object, tag); ... We may set KASAN_KMALLOC_FREE, but not set the track (or even have memory for the track!). The object may not have free meta allocated at all, e.g. very large object with ctor (no place to store meta), or it may be in a mempool: https://elixir.bootlin.com/linux/v5.7-rc6/source/mm/mempool.c#L109 and mempool may be using the object memory itself (for its own next link or something). KASAN_KMALLOC_FREETRACK very explicitly tracks the exact condition we want: we have meta info live now and we have free track set.