From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dy1-f201.google.com (mail-dy1-f201.google.com [74.125.82.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E603436D4F3 for ; Fri, 24 Apr 2026 19:16:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777058214; cv=none; b=Jri+zJMKPujSyKjcNDS+xWef2A79NNku/dCdgk5JAam1NZiy/KjmeuUIPVpOWAToQ2jpweH8oBANCvS8oW4csOKgX5YD3FNAx9aTc5npUOO9DEy4Y32J6jQxFezF8nOzSTK0uppN16GjsZONhmZgoWjZvWB+iuvRclujrojc1Ws= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777058214; c=relaxed/simple; bh=IfRal2g4eax2qipQgHftBuobG7FTGdvuNT9mvVr/54c=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=Y7H7MxgpWYui0ul4LSKvy4rUfeH3za82HdFzplQ9xCXI5I7oDG+gfXJKQjYuI0oHWDbEyDo3FBoxOKo7zW3Bek2xXtyE7DnNrmtE79lSAbd/elBxPTxdRDSC9sBFPaLBehXWZc0FHp1CN8dMSwOH95r4B4QFsz//3tpHRJgMG1Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--stevensd.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=eHoa3mTQ; arc=none smtp.client-ip=74.125.82.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--stevensd.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="eHoa3mTQ" Received: by mail-dy1-f201.google.com with SMTP id 5a478bee46e88-2da19227bc1so17661135eec.1 for ; Fri, 24 Apr 2026 12:16:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1777058212; x=1777663012; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=1KThmIRA5a/VHEqSyhfTRNnbsq/aoBAcBxWfiBbrQ6E=; b=eHoa3mTQXWlmhKG+5czoZE+DxotQANMmkbmngVUPsSy+uhfjWBoiwt0J42z6A30kvY oXT1Q8/ksqwEpxxT7jssLaBGrpU4zWmUZqvNKxQvhOGSBJtZSazVsuqzrtuZnQhB7cV6 kZMk0u4ADOZ4YunR9fcBN8rruLFOjBocokDedfFrpEGO98aTBSmF+DipX8mlOlyXZ2y2 WBQqTOfw42ZT56W3NSB4Wq/n8Agvu8nZ3CzERPwOBnx/tojyzQlewedZxBVdszkv90X8 3gCrHjXyppDLe4meAqciagG2+or+tfC+HFxNLgbut505fBxyAQd+lLNlTlZDHtw/6OxJ swgw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1777058212; x=1777663012; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=1KThmIRA5a/VHEqSyhfTRNnbsq/aoBAcBxWfiBbrQ6E=; b=XSqRwBFbxcHMo4hpPdGhUbJf3SIUGJBA3iPAQNjhARFqN3iUlqnamQyZknH5wBqvKo IEz5QFjVK9vfGfADnTLv54wtVX6ewVq2A+0/5/3PO6zkj9SODMZbigEYLLEmsd6WveVS RwDveXGbqWmqxaSPul7PvVJ/G1VTU2D3bV3U4HzEjBlOzI/q8vouZVOgqAuBqwp6eZbB sbXuR/JrKBiuecPJP91vU7RW9syWJv3WOR6VGwyPqRqVEMp6FpgehAyx4YKxHUCDuQWV 20UZjPKOIDuVddlbJ1mKG9UnwdQAE1AcgAhu1cmakOgtSlDshbkvrwpvG12mqGLLB52d Xzew== X-Forwarded-Encrypted: i=1; AFNElJ8OaI1jATw/YmEHqdaaHoDpVV2s4m9xaBoT9c2+MPj64SgNnL6J0+94kfQ/Y3dMfYjKGCo3dun244J6ruk=@vger.kernel.org X-Gm-Message-State: AOJu0YzCTO5ud2i2MNYjLJJGCJzGjDPp+IxEflRX/Ks0cfAvqDDBNJIH Hj3PnchIXavDMF3nHkgIGVcZGQxaLNPhR3kGdo7CTzOChBYlf7PDdtrJbcGb7TnzYhR2Fh1DaFt 2O/1DqGhwPCcA5A== X-Received: from dlae7.prod.google.com ([2002:a05:701b:2307:b0:12c:211d:3e86]) (user=stevensd job=prod-delivery.src-stubby-dispatcher) by 2002:a05:7022:eac8:b0:12b:ec96:c936 with SMTP id a92af1059eb24-12c73f70bc8mr18556370c88.14.1777058211531; Fri, 24 Apr 2026 12:16:51 -0700 (PDT) Date: Fri, 24 Apr 2026 12:14:45 -0700 In-Reply-To: <20260424191456.2679717-1-stevensd@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260424191456.2679717-1-stevensd@google.com> X-Mailer: git-send-email 2.54.0.rc2.544.gc7ae2d5bb8-goog Message-ID: <20260424191456.2679717-3-stevensd@google.com> Subject: [PATCH v2 02/13] fork: Don't assume fully populated stack during reuse From: David Stevens To: Pasha Tatashin , Linus Walleij , Will Deacon , Quentin Perret , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andy Lutomirski , Xin Li , Peter Zijlstra , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , Kees Cook Cc: David Stevens , linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset="UTF-8" In preparation for dynamic kernel stacks, don't assume that vm_area->nr_pages matches THREAD_SIZE when clearing a stack for reuse. Signed-off-by: David Stevens --- kernel/fork.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index 8961b895bf05..50772c0cc5da 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -332,6 +332,8 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) vm_area = alloc_thread_stack_node_from_cache(tsk, node); if (vm_area) { + unsigned long memset_offset = 0; + if (memcg_charge_kernel_stack(vm_area)) { vfree(vm_area->addr); return -ENOMEM; @@ -343,7 +345,9 @@ static int alloc_thread_stack_node(struct task_struct *tsk, int node) stack = kasan_reset_tag(vm_area->addr); /* Clear stale pointers from reused stack. */ - memset(stack, 0, THREAD_SIZE); + if (!IS_ENABLED(CONFIG_STACK_GROWSUP)) + memset_offset = THREAD_SIZE - vm_area->nr_pages * PAGE_SIZE; + memset(stack + memset_offset, 0, vm_area->nr_pages * PAGE_SIZE); tsk->stack_vm_area = vm_area; tsk->stack = stack; -- 2.54.0.rc2.544.gc7ae2d5bb8-goog