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Fri, 26 Apr 2024 02:20:30 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Xiongwei Song Date: Fri, 26 Apr 2024 17:20:03 +0800 Message-ID: Subject: Re: [PATCH] slub: Fixes freepointer encoding for single free To: Nicolas Bouchinet 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: dbirf9z1resss7gs41wxkxnhtgnkpfn9 X-Rspamd-Queue-Id: 3A9E74000A X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1714123231-118766 X-HE-Meta: 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 zkj332KN uup27Ics6UxNsPcMiLw6kUSHj0+E9gbsLXh+o1ReUroacP8uw8brb9bPZKl0NLZeQbdJwfZi0ubuBDUTLaf+23Q9YrXSeDtHo5XgBTYodU2J79R5lPKbrR1tGeotCc/OI23YCKJkUZHV8e7kJs4pzoU7vx4Rht1CN5X1tE/MQ7uXIQRe6015vz9rWOSH3HNm0dquoy4OJUFgDODsZrpFrJG1ed8QXpBKvxwyrv1C5D/lymiVtYutDqctw8Wc5v8kiSTd6qUPi2/pDo+qpaURHHmTGRQxqOI5v6ERwcQRERIuaa4a/3HRII03Ho6XhpXAFHmX0aPCP+8QdrbrQZzP4Ta0L9DSekLTfcUzr8klfd/Iue35nGVMd65/CJdkm5FZtheXd7p0Pr9kWmvZezIMu2TpQNzdhN66d+9jZxV/5APce8ne2zmt3z48wvBE5HID7IhdXV/OdQqjMVmnXCecm5SQjp7D9vTPF0SqzxAwgtACR49e2nS9zuexEAu+ivgMm52tAkRkk/ZIClxQ= 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 Wed, Apr 24, 2024 at 8:48=E2=80=AFPM 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=3DF` 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=3DFU init_on_free=3D1 log_level=3D7` on the > command line of a kernel build with `CONFIG_SLAB_FREELIST_HARDENED=3Dy`. > > dmesg sample log: > [ 10.708715] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D > [ 10.710323] BUG kmalloc-rnd-05-32 (Tainted: G B T ): Free= pointer corrupt > [ 10.712695] ----------------------------------------------------------= ------------------- > [ 10.712695] > [ 10.712695] Slab 0xffffd8bdc400d580 objects=3D32 used=3D4 fp=3D0xffff9= d9a80356f80 flags=3D0x200000000000a00(workingset|slab|node=3D0|zone=3D2) > [ 10.716698] Object 0xffff9d9a80356600 @offset=3D1536 fp=3D0x7ee4f480ce= 0ecd7c 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=3D0x7ee4f480ce0ecd7c here is beyond kernel memory space, is the issu= e from CONFIG_SLAB_FREELIST_HARDENED enabled? Thanks, Xiongwei > [ 10.716698] > [ 10.716698] Bytes b4 ffff9d9a803565f0: 00 00 00 00 00 00 00 00 00 00 0= 0 00 00 00 00 00 ................ > [ 10.720703] Object ffff9d9a80356600: 00 00 00 00 00 00 00 00 00 00 0= 0 00 00 00 00 00 ................ > [ 10.720703] Object ffff9d9a80356610: 00 00 00 00 00 00 00 00 00 00 0= 0 00 00 00 00 00 ................ > [ 10.724696] Padding ffff9d9a8035666c: 00 00 00 00 00 00 00 00 00 00 0= 0 00 00 00 00 00 ................ > [ 10.724696] Padding ffff9d9a8035667c: 00 00 00 00 = .... > [ 10.724696] FIX kmalloc-rnd-05-32: Object at 0xffff9d9a80356600 not fr= eed > > Signed-off-by: Nicolas Bouchinet > --- > mm/slub.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 3aa12b9b323d9..71dbff9ad8f17 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -4342,10 +4342,16 @@ static __fastpath_inline > void slab_free(struct kmem_cache *s, struct slab *slab, void *object, > unsigned long addr) > { > + bool init =3D false; > + > memcg_slab_free_hook(s, slab, &object, 1); > + init =3D slab_want_init_on_free(s); > > - if (likely(slab_free_hook(s, object, slab_want_init_on_free(s)))) > + if (likely(slab_free_hook(s, object, init))) { > + if (init) > + set_freepointer(s, object, NULL); > do_slab_free(s, slab, object, object, 1, addr); > + } > } > > static __fastpath_inline > -- > 2.44.0 > >