From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 314301C17 for ; Wed, 1 Nov 2023 07:05:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="YjjLTuv/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AEA7CC433C7; Wed, 1 Nov 2023 07:05:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1698822305; bh=j9ykpsBlFRKe7DDjM3F4E4o0mNxil1zOXhS2aCHKGpY=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=YjjLTuv/okiR0psaAHUqPoY3KJE0Gv/tCKYbFkgJeyb0/c+tpUKx31DNUnNenjA7w 6s/plmHRr6YIa6EK1qtNHfQ/Zzk/6z628H5q4SCaF1nNjBfaEekACsBKoWbTGxnkj6 s7fbZnl47gRFwAAgaXkIFGcOvegKVhGlPlQSiEelu40AL15FkE8pp9BWxhgb0/cw6d M7fnP1rqhZyQE7NQPx20WxeguOaxMr7WqpRAEWRkAlqXL8FCgjYQI4wsNn/H2Dj5kl Ov7/yxXdxQFd21AEobNmSkerlr9FQKjoq6Liz3/kzE1ljkqF9R4cXxwIjJVgoKEnsb SJAKIeqWUglow== Message-ID: <5d80e129-b3b3-4bad-b432-897728113bb7@kernel.org> Date: Wed, 1 Nov 2023 16:05:01 +0900 Precedence: bulk X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] riscv: Support RANDOMIZE_KSTACK_OFFSET To: Song Shuai , 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, coelacanthushex@gmail.com Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org References: <20231101064423.1906122-1-songshuaishuai@tinylab.org> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <20231101064423.1906122-1-songshuaishuai@tinylab.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/1/23 15:44, Song Shuai wrote: > 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 > --- > Testing with randomize_kstack_offset=y 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) > } > } > > -asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs) > +asmlinkage __visible __trap_section __no_stack_protector > +void do_trap_ecall_u(struct pt_regs *regs) > { > if (user_mode(regs)) { > + White line change. > long syscall = regs->a7; > > regs->epc += 4; > @@ -308,10 +311,23 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs) > > syscall = syscall_enter_from_user_mode(regs, syscall); > > + add_random_kstack_offset(); > + > if (syscall >= 0 && syscall < NR_syscalls) > syscall_handler(regs, syscall); > else if (syscall != -1) > regs->a0 = -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()); > > syscall_exit_to_user_mode(regs); > } else { -- Damien Le Moal Western Digital Research