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Tue, 15 Sep 2026 07:49:15 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Tue, 15 Sep 2026 16:49:12 +0200 To: "Lorenzo Stoakes (ARM)" , Shaobo Huang Cc: Shaobo Huang , mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, akpm@linux-foundation.org, david@kernel.org, kees@kernel.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, ryabinin.a.a@gmail.com, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Uladzislau Rezki Subject: Re: [PATCH v2] fork: reset pointer tag of vmapped thread stack before vfree Message-ID: References: <20260806123020.90869-1-huangshaobo3@xiaomi.com> <20260914093300.100495-1-huangshaobo3@xiaomi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: EC8C618000D X-Stat-Signature: xq6ymo14s84wmrse4ys81rctjx7bibfi X-Rspam-User: X-HE-Tag: 1789483757-490986 X-HE-Meta: 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 pzKo5feh 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Sep 14, 2026 at 10:44:26AM +0100, Lorenzo Stoakes (ARM) wrote: > +cc Ulad for vmalloc stuff. > > Please don't send a v2 in-reply-to a v1 or any other email. > > Send the patch entirely separately. > > I really need to write a bot to say this :)... > > On Mon, Sep 14, 2026 at 05:33:00PM +0800, Shaobo Huang wrote: > > thread_stack_free_rcu() frees the vmalloc'd thread stack via > > vfree(vm_area->addr). In RCU callback context, vfree() routes to > > vfree_atomic(), which calls llist_add((struct llist_node *)addr, ...) > > and writes 8 bytes to the base of the region being freed. > > > > With KASAN_SW_TAGS, vm_area->addr carries a random tag. If > > kasan_unpoison_task_stack_below() has rewritten the shadow covering > > [base, sp] to KASAN_TAG_KERNEL (0xff) -- which it does on every CPU > > resume for the current task's stack -- the llist_add store checks > > shadow[base] (0xff) against the pointer tag (random) and reports an > > invalid-access, although writing to the base of a stack queued for > > deferred free is legitimate. > > > > Reset the pointer tag to KASAN_TAG_KERNEL before vfree() so that > > kasan_check_range() short-circuits the check, the same way the task > > accesses its own stack at runtime via sp. The vmalloc lookup is safe: > > __find_vmap_area() resets the tag before comparing against va_start. > > > > Fixes: 9f7d416c3612 ("kprobes: Unpoison stack in jprobe_return() for KASAN") > > Cc: stable@vger.kernel.org > > Assisted-by: zhipuai:glm-5.2 > > Thanks for adding this! > > New convention is to say: > > Assisted-by: LLM > > Rather than to list the agent. > > See https://docs.kernel.org/process/coding-assistants.html > > > Signed-off-by: Shaobo Huang > > Looks reasonable to me so, with nits addressed: > > Acked-by: Lorenzo Stoakes (ARM) > > But I would like Ulad's input on this from vmalloc side. > Makes sense to me even though we do it in the __find_vmap_area() but we also use an "addr" in other paths. LGTM: Reviewed-by: Uladzislau Rezki (Sony) -- Uladzislau Rezki