From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f180.google.com (mail-pl1-f180.google.com [209.85.214.180]) (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 627A1218ABD for ; Mon, 28 Jul 2025 16:37:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753720661; cv=none; b=lwt5exddoMXWCNi4ukgXKm8Z4bl2Y7djwdFPU6PoGITSxOfYIS2BAo5XZq9py+LLMipkZCdpo7SJsdLb5adJmfvenN1lyUnCTKALxiM9oqs+SkxjeQ+0A+yC6F7AomC9yiN2eLqCLZBZVnYqdtwRtEvraTwaVJy6AVKccyLnKHI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753720661; c=relaxed/simple; bh=2SCBpxMSnr0Udt96N/nYsntgpWGEdtVpMjRq+5bF/Io=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=hcFFUtgm5tO1JgoekyZavvP3oQdglvSVQEMdJTO4V22GUmm5xIsSNeD8F/v9d+uhQ+ktUzbEsA40n5khnA/tcQgY8Wya+gRPx4h6086VY0jmOPO5XPHZ9hG2b9LhQtyY+GPiSHCjyngKQ1iEDXCAth0dI28OiHe3gQg2z+yriQc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=rivosinc.com; spf=pass smtp.mailfrom=rivosinc.com; dkim=pass (2048-bit key) header.d=rivosinc-com.20230601.gappssmtp.com header.i=@rivosinc-com.20230601.gappssmtp.com header.b=vVFi66ti; arc=none smtp.client-ip=209.85.214.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=rivosinc.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=rivosinc.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=rivosinc-com.20230601.gappssmtp.com header.i=@rivosinc-com.20230601.gappssmtp.com header.b="vVFi66ti" Received: by mail-pl1-f180.google.com with SMTP id d9443c01a7336-2403df11a2aso8049855ad.0 for ; Mon, 28 Jul 2025 09:37:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc-com.20230601.gappssmtp.com; s=20230601; t=1753720658; x=1754325458; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=5q5M+CpT+5kwmRPJ46tyAoXGVagM73LO6ZWHv96bYmU=; b=vVFi66tiWkkBaX51T0jP0+PE1SzQWHC6EG7d1SVIMWrkF2yBdpIlKC3y3RISdPsAXx flcnb8zEyYmHB4neYpKWddQK7ecUX2I94Ug+w6kTsJq0ghJsZYgBozyi/vHTVvx1Q2y8 KA0NBn3KpFhFBm9hMWKM47COZ/YgXeE2Uftzc/WwMVYiPjQu5ASRUGzCzwwesTr+3Pne vZoMIyMF0epLbh2hyNVUhhiwyayfrbp+L348YyW4gOEKEKw9s8M8pkZmNFQnPoqO5CW5 NkY7BdvWrxnU9lsmY5jAI3cFu/MX5mKL1XYaw7JCOMF+nT7Sr6Yh/NBCv4sli2t495oG YRgQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1753720658; x=1754325458; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=5q5M+CpT+5kwmRPJ46tyAoXGVagM73LO6ZWHv96bYmU=; b=A9pl9z3ZSW/5OXPwVMpdwb/6kyEjMKIRv/6X+CVrUB86f/SuL/6Oo35i6jWP0dH60J fOmUIMnk/x4Pt+LUAdoZt14P0FY25Ea9qKYF9Dl5cVmMFeLpWbn8xHHMMjJtp7Fmh9Ps BWWwiwj3u8U8SQMgtZ3HzS+ynTbi/1OvGjRpNXxSvZ4D+FKcEc0CBqBQ4bzfQzT6f5SK yOayEszC+KrXDRygbZFefEDGKZnqo3Dca8pLIwjPAlHTxarxCa5pGda5eDJeg/o/xyTJ OAbTb1kG0v45C8Kvx2961xlgWzxZqaatyrGpw5wGE4znNOLPi9McFRadKezF5YegvUbJ qiXQ== X-Forwarded-Encrypted: i=1; AJvYcCWS89O4HIT9PD67bzNvQFGRBWedobjOce2IM3j4/Et1qX3Q5viNJBKgNXYZ6RhPVU6pNrJ05z5uYVnjBi0=@vger.kernel.org X-Gm-Message-State: AOJu0YxOTVa04llUPPVP+6RidPzApJgk0HfBfsSITS5OBqRy0eX/qMON jg2wFwB7rJ6h1raj55vlqDrPmXk1H1DQ56SUiEvyyartEumUvUibYGUcXMIwmmoOgGk= X-Gm-Gg: ASbGncsZLrAgfwywbvAlK5rAmPq0ualjxZ+dyw4Y4OkB8crpKPSgoZdUmDcRLDXdClD +P0mHPed5ZzZxuh8pMDMkj5fj9phnusQVhOcmXGilDMf9RqKwCqfeyzFRyBOHYKsjWqZOeYMVH5 YkeT7fQwUCK5QAHVAYB9sSfI5wp57b84NQmuqBCf9gbwWUXmA2t8sMljdY4JMrxuSEjg/7lHzzb 92aotMIhl/JDQBq0+Y1c0V4zb4zPD087U93qYTj0FZ/VoXwRia1NYlz4oFdXJwGLUjMRIi8hSbl 2zUq1+0OqB0w+QikJGOAop3LcReW4Psaqfbc6pFCwe4pbARgMMU636wxTWeDYYvICwspiwvLG6j gjRmVhtObgmJzffT5pw5Xk+3m+SNkECXX X-Google-Smtp-Source: AGHT+IG8PkXREALt2B41+CkCZk4vD0+tX/pzcMfIzczJ6dwSMXqtKdHnRzA6w8eQHSP6Yq5Aix/U2Q== X-Received: by 2002:a17:903:1111:b0:23d:dd04:28e2 with SMTP id d9443c01a7336-23fb30cd1f9mr182480625ad.35.1753720658505; Mon, 28 Jul 2025 09:37:38 -0700 (PDT) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-23ff3ea7547sm40412335ad.149.2025.07.28.09.37.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Jul 2025 09:37:37 -0700 (PDT) Date: Mon, 28 Jul 2025 09:37:34 -0700 From: Deepak Gupta To: Will Deacon Cc: Sami Tolvanen , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Masahiro Yamada , Nathan Chancellor , Nicolas Schier , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Nick Desaulniers , Bill Wendling , Monk Chiang , Kito Cheng , Justin Stitt , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-mm@kvack.org, llvm@lists.linux.dev, rick.p.edgecombe@intel.com, broonie@kernel.org, cleger@rivosinc.com, apatel@ventanamicro.com, ajones@ventanamicro.com, conor.dooley@microchip.com, charlie@rivosinc.com, samuel.holland@sifive.com, bjorn@rivosinc.com, fweimer@redhat.com, jeffreyalaw@gmail.com, heinrich.schuchardt@canonical.com, andrew@sifive.com, ved@rivosinc.com Subject: Re: [PATCH 10/11] scs: generic scs code updated to leverage hw assisted shadow stack Message-ID: References: <20250724-riscv_kcfi-v1-0-04b8fa44c98c@rivosinc.com> <20250724-riscv_kcfi-v1-10-04b8fa44c98c@rivosinc.com> <20250725161327.GC1724026@google.com> Precedence: bulk X-Mailing-List: linux-kbuild@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: On Mon, Jul 28, 2025 at 01:47:14PM +0100, Will Deacon wrote: >On Fri, Jul 25, 2025 at 04:13:27PM +0000, Sami Tolvanen wrote: >> On Thu, Jul 24, 2025 at 04:37:03PM -0700, Deepak Gupta wrote: >> > diff --git a/include/linux/scs.h b/include/linux/scs.h >> > index 4ab5bdc898cf..6ceee07c2d1a 100644 >> > --- a/include/linux/scs.h >> > +++ b/include/linux/scs.h >> > @@ -12,6 +12,7 @@ >> > #include >> > #include >> > #include >> > +#include >> > >> > #ifdef CONFIG_SHADOW_CALL_STACK >> > >> > @@ -37,22 +38,45 @@ static inline void scs_task_reset(struct task_struct *tsk) >> > * Reset the shadow stack to the base address in case the task >> > * is reused. >> > */ >> > +#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK >> > + task_scs_sp(tsk) = task_scs(tsk) + SCS_SIZE; >> > +#else >> > task_scs_sp(tsk) = task_scs(tsk); >> > +#endif >> > } >> > >> > static inline unsigned long *__scs_magic(void *s) >> > { >> > +#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK >> > + return (unsigned long *)(s); >> > +#else >> > return (unsigned long *)(s + SCS_SIZE) - 1; >> > +#endif >> > } >> > >> > static inline bool task_scs_end_corrupted(struct task_struct *tsk) >> > { >> > unsigned long *magic = __scs_magic(task_scs(tsk)); >> > - unsigned long sz = task_scs_sp(tsk) - task_scs(tsk); >> > + unsigned long sz; >> > + >> > +#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK >> > + sz = (task_scs(tsk) + SCS_SIZE) - task_scs_sp(tsk); >> > +#else >> > + sz = task_scs_sp(tsk) - task_scs(tsk); >> > +#endif >> > >> > return sz >= SCS_SIZE - 1 || READ_ONCE_NOCHECK(*magic) != SCS_END_MAGIC; >> > } >> > >> > +static inline void __scs_store_magic(unsigned long *s, unsigned long magic_val) >> > +{ >> > +#ifdef CONFIG_ARCH_HAS_KERNEL_SHADOW_STACK >> > + arch_scs_store(s, magic_val); >> > +#else >> > + *__scs_magic(s) = magic_val; >> > +#endif >> > +} >> > + >> >> I'm not a huge fan of all the ifdefs. We could clean this up by >> allowing architectures to simply override some these functions, or at >> least use if (IS_ENABLED(CONFIG...)) instead. Will, any thoughts about >> this? > >Yeah, I agree that allowing architectures to provide overrides makes >sense, however I also suspect that some of this needs to be a runtime >decision because not all CPUs will support the hardware-accelerated >feature and will presumably want to fall back on the software >implementation. Hmm runtime fallback is an important point. Thanks. I'll munch on it a bit. > >Will