From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-dy1-f193.google.com (mail-dy1-f193.google.com [74.125.82.193]) (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 6D5712D77E9 for ; Mon, 26 Jan 2026 20:40:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.82.193 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769460035; cv=none; b=RPjcxWnu2U594OxgxOtJaiM2M0xxWVWIvrZ8Qly1XQxOp68O8xjaSDflv3twyIduGaw5mFa6GW24SwvAgVOPcmqfD7eVpRfeIvjEnaTWatO+/1pPr4TiNoXnhFR1x0jH43inqeattrffJrg8t34NOGOI4WSiDqqI0hCMrW6ByM0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769460035; c=relaxed/simple; bh=aoGpvrsYD8w5a452qvKD8qfj7v0SBwYk6GvPHlbXAj4=; h=Date:From:To:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rWltkHIf2ZklUeT6QBMbJfZt6vDuyQly/zZwJggKyKeneYlalgpf+s55XU0yqVybH9Skw/iYOpNh0uwVrgPqO1iaYCWhi2B5Gg+OHbEkC0B7ZM+OiWfhC7Pcy07GDw1CjrPtkR/XqIbxCH+rvNSNdA/79VmZ99As5h2HtAgd97c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=rivosinc.com; spf=pass smtp.mailfrom=rivosinc.com; dkim=pass (2048-bit key) header.d=rivosinc.com header.i=@rivosinc.com header.b=M9u6mR3/; arc=none smtp.client-ip=74.125.82.193 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (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 header.i=@rivosinc.com header.b="M9u6mR3/" Received: by mail-dy1-f193.google.com with SMTP id 5a478bee46e88-2b74f839bdfso1544698eec.1 for ; Mon, 26 Jan 2026 12:40:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=rivosinc.com; s=google; t=1769460031; x=1770064831; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=EUBpOm0QvKE2389W2MiwDwXvLMg/CnIs37/EZYwRaJU=; b=M9u6mR3/aNK8BZmBX78WRAbvwN6YX+AmG7e/U+MCt8zXKX1hABGR7GOGFerBOXgjZX 77/CVaYNuKSne6efVmMpmK+r+QQdDY2SzRWBMaogGde05d4ZyQmWmMfdavW7+M1fSmdl g0F4nSB2D+NWEb7n4HSJOZUTbT0PrY/zD5giiSQns9V4Cuu4eWsyymBYrq0D8CxWDXY8 eaDPWrkOwbiB0Iukb/pte+2ncblEALdrNUbm7ImZktGVZjzquWfB/mhaCPL29vnyAWQm v3nRGDzCeYlc3rShPpFbmwuZAPuk/xNUCrv7u4OmGEtpPAJPyhY3ABcNashxgffl+32X 2niw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1769460031; x=1770064831; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc:subject :date:message-id:reply-to; bh=EUBpOm0QvKE2389W2MiwDwXvLMg/CnIs37/EZYwRaJU=; b=i22WTNpYIaNbp/NKVltaTmVTxtt4R8xcjaPikQkiI7A1zVVu5TFL3JIO7XT6ya9qks ZKoB8gRqKVN1oNiho2/g/QSWNap5J7IXyH/1kVyKYKvrH78Irf3eMW4Xmyx4nOM4d5WB EgJ8eVsdCagv4YBSdJVw2LL5UMgD5+CGbu1HToFDYilph2F/o3E98FrKVf708NZzF26h UfIeNknkV6KKUkJW32gFQhJp6yKCDfbPUTU8jq/gppoI6iSEsWoMHAyWPRueCgDsqZkG 6UPh6vkRHuuF08Kgy9K4Dp8v59sL4NzNFOt/lU7s5QbSJm9uhEgkdrE+hyvqGrlqceBv nFzQ== X-Forwarded-Encrypted: i=1; AJvYcCX6oewN9U/Zf4pwCyIgjVcdSHysYhEaWecLkkg5/pc1Kp1BQHWSXUZm6/uOaa+aBd8NK2hJubiOY0JRQJ06Ucs=@vger.kernel.org X-Gm-Message-State: AOJu0Yy/nSTGn6V/Jq6uYWs152ZcQG/P732BUQFCV3VA93zA1uttdNWl 8nTUognuQAb9CzTBeFmqoS+zofVAse9l029UzT8wAOIeFMNWlHErISCVKwfeTVrdtaE= X-Gm-Gg: AZuq6aLIYNewYPuDk3cQHL80ZG367RZCApUIsh9gA5OLuZaMNRuhi5QXzBfNGy1R9X5 sVzGKjt3uWDD3XgX5O0SecgG5C8Rw/EjFip3jTBsKUn/heqHw52ptu0DaWB5wPqwDmoaHMqFBOy NwOTkY9oaPC9BLGOcasCu9aLM4+SY5xtZXNJ1EsUV0unqZ5aMMcxEVn1cA6d6maKzn4v8huRlZo I4X8AuaruI5yeDU861m0MZy24drCWq/ErTjdQ+fwy7V7cy6NY7j7qCn4pJZb41IQoKeGO9MdOoy qFNxUeEqUEgGUgBPCk94paOphvIm7LrguwtXHfy8hYPod1XV68cr5YEWadd4Pm3LtaLg31mWe7o ZokTa6CdkZ9HPsAdRAyYa0WegBVqfSDTG/HbS30qNXiEW5vpRnBx3TSv64EYNaxMuysBfN/tH15 2xzzfjX0tSmuAJl2UdKeWpYPKnCfcrxC0= X-Received: by 2002:a05:693c:6218:b0:2ae:5a2e:de70 with SMTP id 5a478bee46e88-2b7638d6573mr2604064eec.8.1769460031398; Mon, 26 Jan 2026 12:40:31 -0800 (PST) Received: from debug.ba.rivosinc.com ([64.71.180.162]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2b73aa03fd0sm15037214eec.23.2026.01.26.12.40.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Jan 2026 12:40:30 -0800 (PST) Date: Mon, 26 Jan 2026 12:40:28 -0800 From: Deepak Gupta To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Lorenzo Stoakes , Paul Walmsley , Palmer Dabbelt , Albert Ou , Conor Dooley , Rob Herring , Krzysztof Kozlowski , Arnd Bergmann , Christian Brauner , Peter Zijlstra , Oleg Nesterov , Eric Biederman , Kees Cook , Jonathan Corbet , Shuah Khan , Jann Horn , Conor Dooley , Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?iso-8859-1?Q?Bj=F6rn?= Roy Baron , Andreas Hindborg , Alice Ryhl , Trevor Gross , Benno Lossin , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, devicetree@vger.kernel.org, linux-arch@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, alistair.francis@wdc.com, richard.henderson@linaro.org, jim.shu@sifive.com, andybnac@gmail.com, kito.cheng@sifive.com, charlie@rivosinc.com, atishp@rivosinc.com, evan@rivosinc.com, cleger@rivosinc.com, alexghiti@rivosinc.com, samitolvanen@google.com, broonie@kernel.org, rick.p.edgecombe@intel.com, rust-for-linux@vger.kernel.org, Zong Li , Andreas Korb , Valentin Haudiquet Subject: Re: [PATCH v26 10/28] riscv/mm: Implement map_shadow_stack() syscall Message-ID: References: <20251211-v5_user_cfi_series-v26-0-f0f419e81ac0@rivosinc.com> <20251211-v5_user_cfi_series-v26-10-f0f419e81ac0@rivosinc.com> Precedence: bulk X-Mailing-List: linux-kselftest@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: <20251211-v5_user_cfi_series-v26-10-f0f419e81ac0@rivosinc.com> Hi Paul/Zong, Can you apply following diff on `allocate_shadow_stack` function in this patch. This fixes the bug that I earlier mentioned. We shouldn't be returning location to token and instead return base address of shadow stack. Userspace consumer should be determining token location itself. This matches the ABI of other arches. Sorry for being late on this. diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c index 27b36034ea85..a8530e6afb1e 100644 --- a/arch/riscv/kernel/usercfi.c +++ b/arch/riscv/kernel/usercfi.c @@ -232,7 +232,7 @@ static unsigned long allocate_shadow_stack(unsigned long addr, unsigned long siz { int flags = MAP_ANONYMOUS | MAP_PRIVATE; struct mm_struct *mm = current->mm; - unsigned long populate, tok_loc = 0; + unsigned long populate; if (addr) flags |= MAP_FIXED_NOREPLACE; @@ -245,13 +245,11 @@ static unsigned long allocate_shadow_stack(unsigned long addr, unsigned long siz if (!set_tok || IS_ERR_VALUE(addr)) goto out; - if (create_rstor_token(addr + token_offset, &tok_loc)) { + if (create_rstor_token(addr + token_offset, NULL)) { vm_munmap(addr, size); return -EINVAL; } - addr = tok_loc; - out: return addr; } On Thu, Dec 11, 2025 at 09:20:43AM -0800, Deepak Gupta via B4 Relay wrote: >From: Deepak Gupta > >As discussed extensively in the changelog for the addition of this >syscall on x86 ("x86/shstk: Introduce map_shadow_stack syscall") the >existing mmap() and madvise() syscalls do not map entirely well onto the >security requirements for shadow stack memory since they lead to windows >where memory is allocated but not yet protected or stacks which are not >properly and safely initialised. Instead a new syscall map_shadow_stack() >has been defined which allocates and initialises a shadow stack page. > >This patch implements this syscall for riscv. riscv doesn't require token >to be setup by kernel because user mode can do that by itself. However to >provide compatibility and portability with other architectues, user mode >can specify token set flag. > >Reviewed-by: Zong Li >Tested-by: Andreas Korb >Tested-by: Valentin Haudiquet >Signed-off-by: Deepak Gupta >--- > arch/riscv/kernel/Makefile | 1 + > arch/riscv/kernel/usercfi.c | 142 ++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 143 insertions(+) > >diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile >index f60fce69b725..2d0e0dcedbd3 100644 >--- a/arch/riscv/kernel/Makefile >+++ b/arch/riscv/kernel/Makefile >@@ -125,3 +125,4 @@ obj-$(CONFIG_ACPI) += acpi.o > obj-$(CONFIG_ACPI_NUMA) += acpi_numa.o > > obj-$(CONFIG_GENERIC_CPU_VULNERABILITIES) += bugs.o >+obj-$(CONFIG_RISCV_USER_CFI) += usercfi.o >diff --git a/arch/riscv/kernel/usercfi.c b/arch/riscv/kernel/usercfi.c >new file mode 100644 >index 000000000000..251c3faccbf8 >--- /dev/null >+++ b/arch/riscv/kernel/usercfi.c >@@ -0,0 +1,142 @@ >+// SPDX-License-Identifier: GPL-2.0 >+/* >+ * Copyright (C) 2024 Rivos, Inc. >+ * Deepak Gupta >+ */ >+ >+#include >+#include >+#include >+#include >+#include >+#include >+#include >+#include >+#include >+#include >+#include >+#include >+ >+#define SHSTK_ENTRY_SIZE sizeof(void *) >+ >+/* >+ * Writes on shadow stack can either be `sspush` or `ssamoswap`. `sspush` can happen >+ * implicitly on current shadow stack pointed to by CSR_SSP. `ssamoswap` takes pointer to >+ * shadow stack. To keep it simple, we plan to use `ssamoswap` to perform writes on shadow >+ * stack. >+ */ >+static noinline unsigned long amo_user_shstk(unsigned long *addr, unsigned long val) >+{ >+ /* >+ * Never expect -1 on shadow stack. Expect return addresses and zero >+ */ >+ unsigned long swap = -1; >+ >+ __enable_user_access(); >+ asm goto(".option push\n" >+ ".option arch, +zicfiss\n" >+ "1: ssamoswap.d %[swap], %[val], %[addr]\n" >+ _ASM_EXTABLE(1b, %l[fault]) >+ ".option pop\n" >+ : [swap] "=r" (swap), [addr] "+A" (*addr) >+ : [val] "r" (val) >+ : "memory" >+ : fault >+ ); >+ __disable_user_access(); >+ return swap; >+fault: >+ __disable_user_access(); >+ return -1; >+} >+ >+/* >+ * Create a restore token on the shadow stack. A token is always XLEN wide >+ * and aligned to XLEN. >+ */ >+static int create_rstor_token(unsigned long ssp, unsigned long *token_addr) >+{ >+ unsigned long addr; >+ >+ /* Token must be aligned */ >+ if (!IS_ALIGNED(ssp, SHSTK_ENTRY_SIZE)) >+ return -EINVAL; >+ >+ /* On RISC-V we're constructing token to be function of address itself */ >+ addr = ssp - SHSTK_ENTRY_SIZE; >+ >+ if (amo_user_shstk((unsigned long __user *)addr, (unsigned long)ssp) == -1) >+ return -EFAULT; >+ >+ if (token_addr) >+ *token_addr = addr; >+ >+ return 0; >+} >+ >+static unsigned long allocate_shadow_stack(unsigned long addr, unsigned long size, >+ unsigned long token_offset, bool set_tok) >+{ >+ int flags = MAP_ANONYMOUS | MAP_PRIVATE; >+ struct mm_struct *mm = current->mm; >+ unsigned long populate, tok_loc = 0; >+ >+ if (addr) >+ flags |= MAP_FIXED_NOREPLACE; >+ >+ mmap_write_lock(mm); >+ addr = do_mmap(NULL, addr, size, PROT_READ, flags, >+ VM_SHADOW_STACK | VM_WRITE, 0, &populate, NULL); >+ mmap_write_unlock(mm); >+ >+ if (!set_tok || IS_ERR_VALUE(addr)) >+ goto out; >+ >+ if (create_rstor_token(addr + token_offset, &tok_loc)) { >+ vm_munmap(addr, size); >+ return -EINVAL; >+ } >+ >+ addr = tok_loc; >+ >+out: >+ return addr; >+} >+ >+SYSCALL_DEFINE3(map_shadow_stack, unsigned long, addr, unsigned long, size, unsigned int, flags) >+{ >+ bool set_tok = flags & SHADOW_STACK_SET_TOKEN; >+ unsigned long aligned_size = 0; >+ >+ if (!cpu_supports_shadow_stack()) >+ return -EOPNOTSUPP; >+ >+ /* Anything other than set token should result in invalid param */ >+ if (flags & ~SHADOW_STACK_SET_TOKEN) >+ return -EINVAL; >+ >+ /* >+ * Unlike other architectures, on RISC-V, SSP pointer is held in CSR_SSP and is available >+ * CSR in all modes. CSR accesses are performed using 12bit index programmed in instruction >+ * itself. This provides static property on register programming and writes to CSR can't >+ * be unintentional from programmer's perspective. As long as programmer has guarded areas >+ * which perform writes to CSR_SSP properly, shadow stack pivoting is not possible. Since >+ * CSR_SSP is writeable by user mode, it itself can setup a shadow stack token subsequent >+ * to allocation. Although in order to provide portablity with other architecture (because >+ * `map_shadow_stack` is arch agnostic syscall), RISC-V will follow expectation of a token >+ * flag in flags and if provided in flags, setup a token at the base. >+ */ >+ >+ /* If there isn't space for a token */ >+ if (set_tok && size < SHSTK_ENTRY_SIZE) >+ return -ENOSPC; >+ >+ if (addr && (addr & (PAGE_SIZE - 1))) >+ return -EINVAL; >+ >+ aligned_size = PAGE_ALIGN(size); >+ if (aligned_size < size) >+ return -EOVERFLOW; >+ >+ return allocate_shadow_stack(addr, aligned_size, size, set_tok); >+} > >-- >2.43.0 > >