From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A30284E06E1; Wed, 16 Sep 2026 20:59:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789592413; cv=none; b=I4aOZlV/TYQEJ/c0sCPdZt1+0IcbcxU7/W8eunjIkVTiDO/2CyvBM6iMLCcCIqgy+DdRQ0SUBVgH5YWGFsrq4lT6xEWW8H2BJIeQE9s5TheQb+H3D9YA4qFxcaClyiH3cUFKhMeh2fXLVdb1zW2CXdYCDe+iZaphg3n40cpwlcg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789592413; c=relaxed/simple; bh=QzA+KBr/uIcAC8kLbo5Ay7GDGttYSV8buA8FcdHeVQ0=; h=Date:To:From:Subject:Message-Id; b=OiHR88j1dsB81lBuVyyuKjVBGfHqPMT9d5TWS+RaT8z4pmLS15rRV51bouvmlMnYH/ZpMF2JQSSIT+vS88d2GcI8WMqxQEdEHr4ZhqF7M1jjVecw5w//DO0BWidvtJczqY/1AYzHCcFzY0gAK4NWbRkjrCjovTe7bcMZtH9q0rk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=zaBK33CL; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="zaBK33CL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1EE111F000FF; Wed, 16 Sep 2026 20:59:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789592397; bh=dbpskzbIoTd5IgRyVcqGXoJDpMKNH4vuWYhLV20/QOU=; h=Date:To:From:Subject; b=zaBK33CLHVz1dbnKb/QMYF993VmqH0ZZDED6LzBTv6VntRppIsbvZzahTmqZI2AL8 k6Ukq25+ZIFvMPSGpX52m25512KJnCL3PJBq1n1aNd451GhWVAec/7Ar0X5fuWV+Ce 1SfCm00WECTqFwcKBBvrKqYhDwkSJtXSKI+0YJME= Date: Wed, 16 Sep 2026 13:59:56 -0700 To: mm-commits@vger.kernel.org,vincenzo.frascino@arm.com,stable@vger.kernel.org,ljs@kernel.org,huangshaobo3@xiaomi.com,glider@google.com,dvyukov@google.com,david@kernel.org,andreyknvl@gmail.com,ryabinin.a.a@gmail.com,akpm@linux-foundation.org From: Andrew Morton Subject: + kasan-unpoison-task-stack-below-watermark-only-in-generic-mode.patch added to mm-hotfixes-unstable branch Message-Id: <20260916205957.1EE111F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: kasan: unpoison task stack below watermark only in generic mode has been added to the -mm mm-hotfixes-unstable branch. Its filename is kasan-unpoison-task-stack-below-watermark-only-in-generic-mode.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/kasan-unpoison-task-stack-below-watermark-only-in-generic-mode.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Andrey Ryabinin Subject: kasan: unpoison task stack below watermark only in generic mode Date: Wed, 16 Sep 2026 19:51:13 +0200 CPU resume and BPF exception handling can discard stack frames without running their compiler-generated epilogues. Generic KASAN needs kasan_unpoison_task_stack_below() to clear the redzones left behind by those frames before the stack is reused. CONFIG_KASAN_STACK also enables this helper for SW_TAGS. The helper derives the stack base from an untagged stack pointer, so kasan_unpoison() writes KASAN_TAG_KERNEL (0xff) into the shadow for [base, watermark). For a vmapped task stack, vm_area->addr still carries the original random allocation tag. This creates a tag mismatch at the stack base even if that memory has never held an instrumented stack object. When the task exits and its stack is not cached, thread_stack_free_rcu() passes vm_area->addr to vfree(). In RCU callback context this reaches vfree_atomic(), whose llist_add() writes to the allocation base through the tagged pointer and triggers a false KASAN invalid-access report: BUG: KASAN: invalid-access in vfree_atomic+0x90/0x150 Write of size 8 at addr c2ffffc0a8f70000 by task rcuop/7/75 Pointer tag: [c2], memory tag: [ff] Call trace: __hwasan_store8_noabort+0xe8/0xf8 vfree_atomic+0x90/0x150 vfree+0x220/0x298 thread_stack_free_rcu+0x3c/0x4c rcu_do_batch+0x308/0xaf0 rcu_nocb_cb_kthread+0x33c/0x708 The deferred-free path started using the tagged vm_area->addr in commit 449e0b4ed5a1 ("fork: clean-up naming of vm_stack/vm_struct variables in vmap stacks code"). Previously it freed the untagged pointer derived from tsk->stack, so the write was never tag-checked. SW_TAGS does not need the blanket shadow reset to make subsequent stack accesses valid: untagged kernel pointers have the match-all 0xff tag, and the compiler initializes the shadow tags of instrumented stack objects before use. Return early unless CONFIG_KASAN_GENERIC is enabled. Keep the mode check in the common helper so it covers both resume and bpf_throw(). Link: https://lore.kernel.org/20260916175113.1327454-1-ryabinin.a.a@gmail.com Fixes: 449e0b4ed5a1 ("fork: clean-up naming of vm_stack/vm_struct variables in vmap stacks code") Signed-off-by: Andrey Ryabinin Signed-off-by: Andrew Morton Reported-by: Shaobo Huang Closes: https://lore.kernel.org/all/20260806123020.90869-1-huangshaobo3@xiaomi.com/ Assisted-by: LLM Cc: Alexander Potapenko Cc: Andrey Konovalov Cc: David Hildenbrand Cc: Dmitry Vyukov Cc: Lorenzo Stoakes Cc: Vincenzo Frascino Cc: --- mm/kasan/common.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) --- a/mm/kasan/common.c~kasan-unpoison-task-stack-below-watermark-only-in-generic-mode +++ a/mm/kasan/common.c @@ -114,12 +114,23 @@ void kasan_unpoison_task_stack(struct ta /* Unpoison the stack for the current task beyond a watermark sp value. */ asmlinkage void kasan_unpoison_task_stack_below(const void *watermark) { + void *base; + + /* + * Only the generic mode needs this. In the tag-based mode the + * compiler fully initializes the shadow of stack variables on + * function entry, so stale tags left below the watermark are + * harmless. + */ + if (!IS_ENABLED(CONFIG_KASAN_GENERIC)) + return; + /* * Calculate the task stack base address. Avoid using 'current' * because this function is called by early resume code which hasn't * yet set up the percpu register (%gs). */ - void *base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1)); + base = (void *)((unsigned long)watermark & ~(THREAD_SIZE - 1)); kasan_unpoison(base, watermark - base, false); } _ Patches currently in -mm which might be from ryabinin.a.a@gmail.com are kasan-unpoison-task-stack-below-watermark-only-in-generic-mode.patch