From nobody Wed Dec 17 09:46:55 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8D935C4332F for ; Wed, 1 Nov 2023 06:45:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345303AbjKAGpq (ORCPT ); Wed, 1 Nov 2023 02:45:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44012 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343684AbjKAGpo (ORCPT ); Wed, 1 Nov 2023 02:45:44 -0400 Received: from bg4.exmail.qq.com (bg4.exmail.qq.com [43.155.65.254]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18B1E103; Tue, 31 Oct 2023 23:45:37 -0700 (PDT) X-QQ-mid: bizesmtp68t1698821091tvb7u4r1 Received: from localhost.localdomain ( [58.240.82.166]) by bizesmtp.qq.com (ESMTP) with id ; Wed, 01 Nov 2023 14:44:48 +0800 (CST) X-QQ-SSF: 01200000000000B0B000000A0000000 X-QQ-FEAT: 3M0okmaRx3gxeEyH4BlqDeuloEyl32NdDWDCAwDSyK64HTzX/3liUnbfNDiz+ sZcpbjY9p5B/dZFk8H1lKOIoJPxcVegVfzk/66o6v+sV5lnjG+djsJVpkmIsWpTilez6PcS wG3rH0s0qeISm34gMMW7Go0eab9EqbwaAlsjo94pCL5VpmuSmwp2+iwsJ5sRc0YjK2EEyDN 4R+SsAo1eIxe5XgTejVkfuUJ6+ZT1PHSIaZss+kefmd4Xf9X2WUwuwkgOX38HUg15MtAUpP PZf2IJt4k0wS46++jcBsUH9D7+VWfWyVlvdL17lk8A2jZTCExwkSVprmWwImL8NK2Ejo5ZT kmTeZiNuWGehdme6164H/Yg2vxnQE5o7szoeegp X-QQ-GoodBg: 0 X-BIZMAIL-ID: 1492668164630438734 From: Song Shuai To: paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, keescook@chromium.org, guoren@kernel.org, bjorn@rivosinc.com, jszhang@kernel.org, conor.dooley@microchip.com, andy.chiu@sifive.com, samitolvanen@google.com, songshuaishuai@tinylab.org, coelacanthushex@gmail.com Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: [PATCH] riscv: Support RANDOMIZE_KSTACK_OFFSET Date: Wed, 1 Nov 2023 14:44:23 +0800 Message-Id: <20231101064423.1906122-1-songshuaishuai@tinylab.org> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:tinylab.org:qybglogicsvrsz:qybglogicsvrsz4a-0 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Inspired from arm64's implement -- commit 70918779aec9 ("arm64: entry: Enable random_kstack_offset support") Add support of kernel stack offset randomization while handling syscall, the offset is defaultly limited by KSTACK_OFFSET_MAX() (i.e. 10 bits). In order to avoid trigger stack canaries (due to __builtin_alloca) and slowing down the entry path, use __no_stack_protector attribute to disable stack protector for do_trap_ecall_u() at the function level. Signed-off-by: Song Shuai Acked-by: Palmer Dabbelt Reviewed-by: Kees Cook Reviewed-by: Palmer Dabbelt --- Testing with randomize_kstack_offset=3Dy cmdline, lkdtm/stack-entropy.sh showed appropriate stack offset instead of zero. --- arch/riscv/Kconfig | 1 + arch/riscv/kernel/traps.c | 18 +++++++++++++++++- 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index d607ab0f7c6d..0e843de33f0c 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -100,6 +100,7 @@ config RISCV select HAVE_ARCH_KGDB_QXFER_PKT select HAVE_ARCH_MMAP_RND_BITS if MMU select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT + select HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET select HAVE_ARCH_SECCOMP_FILTER select HAVE_ARCH_THREAD_STRUCT_WHITELIST select HAVE_ARCH_TRACEHOOK diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c index 19807c4d3805..3f869b2d47c3 100644 --- a/arch/riscv/kernel/traps.c +++ b/arch/riscv/kernel/traps.c @@ -6,6 +6,7 @@ #include #include #include +#include #include #include #include @@ -296,9 +297,11 @@ asmlinkage __visible __trap_section void do_trap_break= (struct pt_regs *regs) } } =20 -asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *r= egs) +asmlinkage __visible __trap_section __no_stack_protector +void do_trap_ecall_u(struct pt_regs *regs) { if (user_mode(regs)) { + long syscall =3D regs->a7; =20 regs->epc +=3D 4; @@ -308,10 +311,23 @@ asmlinkage __visible __trap_section void do_trap_ecal= l_u(struct pt_regs *regs) =20 syscall =3D syscall_enter_from_user_mode(regs, syscall); =20 + add_random_kstack_offset(); + if (syscall >=3D 0 && syscall < NR_syscalls) syscall_handler(regs, syscall); else if (syscall !=3D -1) regs->a0 =3D -ENOSYS; + /* + * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(), + * so the maximum stack offset is 1k bytes (10 bits). + * + * The actual entropy will be further reduced by the compiler when + * applying stack alignment constraints: 16-byte (i.e. 4-bit) aligned + * for RV32I or RV64I. + * + * The resulting 6 bits of entropy is seen in SP[9:4]. + */ + choose_random_kstack_offset(get_random_u16()); =20 syscall_exit_to_user_mode(regs); } else { --=20 2.20.1