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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=clip-os.org; s=gm1; t=1714377358; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=qRFrm6wJpTdJo02mNwFpZgTYCwsjhC4CDet4zevy5n8=; b=ZVb+L3fwl4phMyrApv6CGFbaRYimX1adE0s/u893Huzsi1cR9O/9q8yOIyvqdp+yDwWoFv abkLETToqKRrwLM1ecrEyLXs6IJDiDu/ajqjfNntI6qLAk9KHd6nE6TRZqMHHKexLQmy3g Pdrfkdr8CjpBqmdzcThNs2fTAn4oCrC4eUPVyP5r9/uMGt6ObZXo4UEGElZD268RBXgSwr B4v1XR7mPz6LBsGtgTrkveLfhTK5BjXYZHdWu1Otpr8egk9e2jLtpQeafik03iC+unr5N/ pg8fIe1yMk4DN0xjO+fOTi4lTM3rUaV0m73eQ5W5jRzwPvvjLS/SFEjwUn3+fQ== Message-ID: <1136cf64-c1b6-4909-b64e-0c754276024c@clip-os.org> Date: Mon, 29 Apr 2024 09:55:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] slub: Fixes freepointer encoding for single free To: Xiongwei Song Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com References: <47011bf2-4000-4fd8-9dd3-4c6b6a1c4a80@clip-os.org> Content-Language: en-US From: Nicolas Bouchinet In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-GND-Sasl: nicolas.bouchinet@clip-os.org X-Rspamd-Server: rspam01 X-Stat-Signature: ms14txu81as16fjys4w498sx71dkhhao X-Rspam-User: X-Rspamd-Queue-Id: 6F1E94001B X-HE-Tag: 1714377360-830043 X-HE-Meta: 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 ZKJAwpgI vWeVwWWLGElGJdt6XZHyO1pZbdXcGM/NE3Djf7wWpz8tQoEdu4ub2mHL+zuL5w7Y7hDAd4sKGuYmSl3VG6+t+mXDSNM09Jgejr1/x2M8r8Q77xZQ+Ku+kzLNJ1+xoCOAUTPb/z84GkHhRU+GH3W0+xmEIDbHGTX65CHznU7DtqfNkGiCfHL040XFMn2i2En96uOI7zIQQYLsgST1Tppx+SMYK4xyndFLtNnWEUyhb0E1QOT9Ewom8PDFJrEkO93TZbcKgoTjJznecRXlPmPueFgEudL8ZStgWImGf1Pc8oYpG03DJ+/QxIZutbBOKKUQs53TAIZn6Hxr+NVhTAhlB8M1KKw== 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: List-Subscribe: List-Unsubscribe: On 4/26/24 15:14, Xiongwei Song wrote: > On Fri, Apr 26, 2024 at 8:18 PM Nicolas Bouchinet > wrote: >> On 4/26/24 11:20, Xiongwei Song wrote: >>> On Wed, Apr 24, 2024 at 8:48 PM Nicolas Bouchinet >>> wrote: >>>> From: Nicolas Bouchinet >>>> >>>> Commit 284f17ac13fe ("mm/slub: handle bulk and single object freeing >>>> separately") splits single and bulk object freeing in two functions >>>> slab_free() and slab_free_bulk() which leads slab_free() to call >>>> slab_free_hook() directly instead of slab_free_freelist_hook(). >>>> >>>> If `init_on_free` is set, slab_free_hook() zeroes the object. >>>> Afterward, if `slub_debug=F` and `CONFIG_SLAB_FREELIST_HARDENED` are >>>> set, the do_slab_free() slowpath executes freelist consistency >>>> checks and try to decode a zeroed freepointer which leads to a >>>> "Freepointer corrupt" detection in check_object(). >>>> >>>> Object's freepointer thus needs to be properly set using >>>> set_freepointer() after init_on_free. >>>> >>>> To reproduce, set `slub_debug=FU init_on_free=1 log_level=7` on the >>>> command line of a kernel build with `CONFIG_SLAB_FREELIST_HARDENED=y`. >>>> >>>> dmesg sample log: >>>> [ 10.708715] ============================================================================= >>>> [ 10.710323] BUG kmalloc-rnd-05-32 (Tainted: G B T ): Freepointer corrupt >>>> [ 10.712695] ----------------------------------------------------------------------------- >>>> [ 10.712695] >>>> [ 10.712695] Slab 0xffffd8bdc400d580 objects=32 used=4 fp=0xffff9d9a80356f80 flags=0x200000000000a00(workingset|slab|node=0|zone=2) >>>> [ 10.716698] Object 0xffff9d9a80356600 @offset=1536 fp=0x7ee4f480ce0ecd7c >>> If init_on_free is set, slab_free_hook() zeros the object first, then >>> do_slab_free() calls >>> set_freepointer() to set the fp value, so there are 8 bytes non-zero >>> at the moment? >>> Hence, the issue is not related to init_on_free? >>> >>> The fp=0x7ee4f480ce0ecd7c here is beyond kernel memory space, is the issue from >>> CONFIG_SLAB_FREELIST_HARDENED enabled? >> My understanding of the bug is that slab_free_hook() indeed zeroes the >> object and its metadata first, then calls do_slab_free() and directly >> calls __slab_free(), head an tail parameters being set to the object. >> >> If `slub_debug=F` (SLAB_CONSISTENCY_CHECKS) is set, the following call >> path can be executed : >> >> free_to_partial_list() -> >> >> free_debug_processing() -> >> >> free_consistency_checks() -> >> >> check_object() -> >> >> check_valid_pointer(get_freepointer()) > I understand the call path. I meant here the freepointer is not ZERO > but an illegal > value( fp=0x7ee4f480ce0ecd7c), Yes this is the reason of this patch. The freepointer is an illegal value because the memory range where it sits has been overridden by zeroes, set_freepointer() is never called and thus the freepointer is never properly set.  The illegal value is obtained after zeroes has been decoded by get_freepointer()->freelist_ptr_decode(). > then check_valid_pointer return 1 with > it's last line > and then check_object() printed out the error message. I'm not sure if I > misunderstood you. check_valid_pointer() returns 0 since object < base, the object being the decoded fp (0x7ee4f480ce0ecd7c < 0xffff.* base addr), hence check_object() returns 0, not 1. This is why the "Object at 0x%p not freed" slab_fix() is called in free_debug_processing(). > > Thank, > Xiongwei >