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d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=Zr5Zwdnm9g0v0RoWFdb/Hft1niHdwCm4sqYnYTlZRA0=; b=HUdtk3dOAv3VUPO46yagLxhl10zmZSn+EQQIetWxjQ6YxqxKkqaIUI98FJ5LQuOWO/ eWGR1HmyMu+JYTBBJl+TOcBX1SGwTsVG2YKDrLCFPxLY8r6z0jH2+6mdW2sApL7CXXym 2E4wruipCcSnS0UK4FrkF0WjGSz8lt66y0hU0sRPk1j0OZzIoDhRHUyvwCETUOOMaQwt 5icDt80+tiXOjBR0An24/iUkjAI7Wb03+69pDpFEcrxGycmM8BXx+NaVdxNhWNroClHw PIb5tFDF61i+jks5yS/RwiY5KoW/HKUytCvy4ucd0f6tce6XlBv5kVgwPqN8M4i1VYHm f8Ww== X-Gm-Message-State: AOAM531Xfwv/F6w0aL5q84lVv+/mHgug59HmmmBkMkTYGFknzgMDnsMK XBst61I8Kephtx2zdLCU33mizcOTtpUgZ2JAt9AKUQ== X-Google-Smtp-Source: ABdhPJw8b30PxRuXNHPWCgSoAq0sYHVucwIBErjKYF4ve78qZaiDmTiLrDDHpTCjOXqRjFaoxGsq8HIpFSxFRy2RTCM= X-Received: by 2002:a05:620a:15ce:: with SMTP id o14mr19106447qkm.231.1605597212067; Mon, 16 Nov 2020 23:13:32 -0800 (PST) MIME-Version: 1.0 References: <1605508168-7418-1-git-send-email-Kuan-Ying.Lee@mediatek.com> <1605508168-7418-2-git-send-email-Kuan-Ying.Lee@mediatek.com> <1605595583.29084.24.camel@mtksdccf07> In-Reply-To: <1605595583.29084.24.camel@mtksdccf07> From: Dmitry Vyukov Date: Tue, 17 Nov 2020 08:13:20 +0100 Message-ID: Subject: Re: [PATCH v2 1/1] kasan: fix object remain in offline per-cpu quarantine To: Kuan-Ying Lee Cc: Andrey Ryabinin , Alexander Potapenko , Andrew Morton , Matthias Brugger , kasan-dev , Linux-MM , LKML , Linux ARM , linux-mediatek@lists.infradead.org, nicholas.tang@mediatek.com, Miles Chen , guangye.yang@mediatek.com, wsd_upstream 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 Tue, Nov 17, 2020 at 7:46 AM Kuan-Ying Lee wrote: > > On Mon, 2020-11-16 at 10:26 +0100, Dmitry Vyukov wrote: > > On Mon, Nov 16, 2020 at 7:30 AM Kuan-Ying Lee > > wrote: > > > > > > We hit this issue in our internal test. > > > When enabling generic kasan, a kfree()'d object is put into per-cpu > > > quarantine first. If the cpu goes offline, object still remains in > > > the per-cpu quarantine. If we call kmem_cache_destroy() now, slub > > > will report "Objects remaining" error. > > > > > > [ 74.982625] ============================================================================= > > > [ 74.983380] BUG test_module_slab (Not tainted): Objects remaining in test_module_slab on __kmem_cache_shutdown() > > > [ 74.984145] ----------------------------------------------------------------------------- > > > [ 74.984145] > > > [ 74.984883] Disabling lock debugging due to kernel taint > > > [ 74.985561] INFO: Slab 0x(____ptrval____) objects=34 used=1 fp=0x(____ptrval____) flags=0x2ffff00000010200 > > > [ 74.986638] CPU: 3 PID: 176 Comm: cat Tainted: G B 5.10.0-rc1-00007-g4525c8781ec0-dirty #10 > > > [ 74.987262] Hardware name: linux,dummy-virt (DT) > > > [ 74.987606] Call trace: > > > [ 74.987924] dump_backtrace+0x0/0x2b0 > > > [ 74.988296] show_stack+0x18/0x68 > > > [ 74.988698] dump_stack+0xfc/0x168 > > > [ 74.989030] slab_err+0xac/0xd4 > > > [ 74.989346] __kmem_cache_shutdown+0x1e4/0x3c8 > > > [ 74.989779] kmem_cache_destroy+0x68/0x130 > > > [ 74.990176] test_version_show+0x84/0xf0 > > > [ 74.990679] module_attr_show+0x40/0x60 > > > [ 74.991218] sysfs_kf_seq_show+0x128/0x1c0 > > > [ 74.991656] kernfs_seq_show+0xa0/0xb8 > > > [ 74.992059] seq_read+0x1f0/0x7e8 > > > [ 74.992415] kernfs_fop_read+0x70/0x338 > > > [ 74.993051] vfs_read+0xe4/0x250 > > > [ 74.993498] ksys_read+0xc8/0x180 > > > [ 74.993825] __arm64_sys_read+0x44/0x58 > > > [ 74.994203] el0_svc_common.constprop.0+0xac/0x228 > > > [ 74.994708] do_el0_svc+0x38/0xa0 > > > [ 74.995088] el0_sync_handler+0x170/0x178 > > > [ 74.995497] el0_sync+0x174/0x180 > > > [ 74.996050] INFO: Object 0x(____ptrval____) @offset=15848 > > > [ 74.996752] INFO: Allocated in test_version_show+0x98/0xf0 age=8188 cpu=6 pid=172 > > > [ 75.000802] stack_trace_save+0x9c/0xd0 > > > [ 75.002420] set_track+0x64/0xf0 > > > [ 75.002770] alloc_debug_processing+0x104/0x1a0 > > > [ 75.003171] ___slab_alloc+0x628/0x648 > > > [ 75.004213] __slab_alloc.isra.0+0x2c/0x58 > > > [ 75.004757] kmem_cache_alloc+0x560/0x588 > > > [ 75.005376] test_version_show+0x98/0xf0 > > > [ 75.005756] module_attr_show+0x40/0x60 > > > [ 75.007035] sysfs_kf_seq_show+0x128/0x1c0 > > > [ 75.007433] kernfs_seq_show+0xa0/0xb8 > > > [ 75.007800] seq_read+0x1f0/0x7e8 > > > [ 75.008128] kernfs_fop_read+0x70/0x338 > > > [ 75.008507] vfs_read+0xe4/0x250 > > > [ 75.008990] ksys_read+0xc8/0x180 > > > [ 75.009462] __arm64_sys_read+0x44/0x58 > > > [ 75.010085] el0_svc_common.constprop.0+0xac/0x228 > > > [ 75.011006] kmem_cache_destroy test_module_slab: Slab cache still has objects > > > > > > Register a cpu hotplug function to remove all objects in the offline > > > per-cpu quarantine when cpu is going offline. Set a per-cpu variable > > > to indicate this cpu is offline. > > > > > > Signed-off-by: Kuan-Ying Lee > > > Suggested-by: Dmitry Vyukov > > > Reported-by: Guangye Yang > > > Cc: Andrey Ryabinin > > > Cc: Alexander Potapenko > > > Cc: Andrew Morton > > > Cc: Matthias Brugger > > > --- > > > mm/kasan/quarantine.c | 35 +++++++++++++++++++++++++++++++++++ > > > 1 file changed, 35 insertions(+) > > > > > > diff --git a/mm/kasan/quarantine.c b/mm/kasan/quarantine.c > > > index 4c5375810449..16e618ea805e 100644 > > > --- a/mm/kasan/quarantine.c > > > +++ b/mm/kasan/quarantine.c > > > @@ -29,6 +29,7 @@ > > > #include > > > #include > > > #include > > > +#include > > > > > > #include "../slab.h" > > > #include "kasan.h" > > > @@ -43,6 +44,7 @@ struct qlist_head { > > > struct qlist_node *head; > > > struct qlist_node *tail; > > > size_t bytes; > > > + bool offline; > > > }; > > > > > > #define QLIST_INIT { NULL, NULL, 0 } > > > @@ -188,6 +190,11 @@ void quarantine_put(struct kasan_free_meta *info, struct kmem_cache *cache) > > > local_irq_save(flags); > > > > > > q = this_cpu_ptr(&cpu_quarantine); > > > + if (q->offline) { > > > + qlink_free(&info->quarantine_link, cache); > > > + local_irq_restore(flags); > > > + return; > > > + } > > I think we need to make sure objects will not be put in per-cpu > quarantine which is offline. > > > > qlist_put(q, &info->quarantine_link, cache->size); > > > if (unlikely(q->bytes > QUARANTINE_PERCPU_SIZE)) { > > > qlist_move_all(q, &temp); > > > @@ -328,3 +335,31 @@ void quarantine_remove_cache(struct kmem_cache *cache) > > > > > > synchronize_srcu(&remove_cache_srcu); > > > } > > > + > > > +static int kasan_cpu_online(unsigned int cpu) > > > +{ > > > + this_cpu_ptr(&cpu_quarantine)->offline = false; > > > + return 0; > > > +} > > > + > > > +static int kasan_cpu_offline(unsigned int cpu) > > > +{ > > > + struct qlist_head *q; > > > + > > > + q = this_cpu_ptr(&cpu_quarantine); > > > + q->offline = true; > > > + qlist_free_all(q, NULL); > > > > Looks much nicer now! > > > > What is the story with interrupts in these callbacks? > > In the previous patch you mentioned that this CPU can still receive > > interrupts for a brief period of time. If these interrupts also free > > something, can't we corrupt the per-cpu quarantine? In quarantine_put > > we protect it by disabling interrupts I think. > > > > Here is a situation. > After we freed all objects from the per-cpu quarantine which is going > offline, the interrupts happened. These interrupts free something and > put objects into this per-cpu quarantine. If we call > kmem_cache_destroy() now, slub still detect objects remain in > the per-cpu quarantine and report "Object remaining" error. > > Thus, we need to check q->offline in quarantine_put and make sure > the offline per-cpu quarantine is not corrupted. If an interrupt can happen later, can't it happen right during our call to qlist_free_all and corrupt the per-cpu cache? Perhaps we need something like: // ... explain the subtleness ... WRITE_ONCE(q->offline, true); barrier(); qlist_free_all(q, NULL); ? > > > + return 0; > > > +} > > > + > > > +static int __init kasan_cpu_offline_quarantine_init(void) > > > +{ > > > + int ret = 0; > > > + > > > + ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/kasan:online", > > > + kasan_cpu_online, kasan_cpu_offline); > > > + if (ret < 0) > > > + pr_err("kasan offline cpu quarantine register failed [%d]\n", ret); > > > + return ret; > > > +} > > > +late_initcall(kasan_cpu_offline_quarantine_init); > > > -- > > > 2.18.0