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 48BDC7C092; Mon, 8 Apr 2024 13:46:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712583984; cv=none; b=g5g2F2t97iTeiNjfnbcHWxibeWBVceoNOg1SpvYosBhReFt5BSrKYaIPt53crhD7d2wSGBVFN1NQqC70WFbtHuxgqzz9MQ/eEpBwopAa7CoiPnqEcBHHUytotlgCs82s/YwVqmba0SSMqOVVpOUUEuWU1OcstQYlOsvJaoKszEY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712583984; c=relaxed/simple; bh=TFOFUTjoq5AvmFApFGglUmCcMx49A2WDDaIXIGD6Dmw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ErKRrBJ+Jb7MqNH4UcJociIFCJxzL4ZkN8XuQr+c3nN6e/5nCS47Pn5XPFxNDh52WZUiJzwtItcaQO0kMM4QUahZsrA+I56f1myJ7y9h4SScBCn3D1Dxqfyvf/NiL3hI5CDMEd2Zcw/xPFvoAAVGfbnxHI0C7eT6OPBNLuqkHUA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=FLePy6r5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="FLePy6r5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C324EC433F1; Mon, 8 Apr 2024 13:46:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1712583984; bh=TFOFUTjoq5AvmFApFGglUmCcMx49A2WDDaIXIGD6Dmw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FLePy6r5XOH/8UcFrwM6vZF+rpJ25liJCgk2XEB0w8OVkna+yJJ3TYhH3kDUF35sQ 941qdTBsdX1y6qPFcWpJFEc8nMGuekbIm4LHmlQM6peZ9pXkeXu8tDCQm7W1tWpsbA cHEKF1VblP1IjjWwzTwMl2pXHtERsJzVT3rZjeNk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Stefan ORear , Alexandre Ghiti , Palmer Dabbelt Subject: [PATCH 6.8 242/273] riscv: process: Fix kernel gp leakage Date: Mon, 8 Apr 2024 14:58:37 +0200 Message-ID: <20240408125316.949618033@linuxfoundation.org> X-Mailer: git-send-email 2.44.0 In-Reply-To: <20240408125309.280181634@linuxfoundation.org> References: <20240408125309.280181634@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.8-stable review patch. If anyone has any objections, please let me know. ------------------ From: Stefan O'Rear commit d14fa1fcf69db9d070e75f1c4425211fa619dfc8 upstream. childregs represents the registers which are active for the new thread in user context. For a kernel thread, childregs->gp is never used since the kernel gp is not touched by switch_to. For a user mode helper, the gp value can be observed in user space after execve or possibly by other means. [From the email thread] The /* Kernel thread */ comment is somewhat inaccurate in that it is also used for user_mode_helper threads, which exec a user process, e.g. /sbin/init or when /proc/sys/kernel/core_pattern is a pipe. Such threads do not have PF_KTHREAD set and are valid targets for ptrace etc. even before they exec. childregs is the *user* context during syscall execution and it is observable from userspace in at least five ways: 1. kernel_execve does not currently clear integer registers, so the starting register state for PID 1 and other user processes started by the kernel has sp = user stack, gp = kernel __global_pointer$, all other integer registers zeroed by the memset in the patch comment. This is a bug in its own right, but I'm unwilling to bet that it is the only way to exploit the issue addressed by this patch. 2. ptrace(PTRACE_GETREGSET): you can PTRACE_ATTACH to a user_mode_helper thread before it execs, but ptrace requires SIGSTOP to be delivered which can only happen at user/kernel boundaries. 3. /proc/*/task/*/syscall: this is perfectly happy to read pt_regs for user_mode_helpers before the exec completes, but gp is not one of the registers it returns. 4. PERF_SAMPLE_REGS_USER: LOCKDOWN_PERF normally prevents access to kernel addresses via PERF_SAMPLE_REGS_INTR, but due to this bug kernel addresses are also exposed via PERF_SAMPLE_REGS_USER which is permitted under LOCKDOWN_PERF. I have not attempted to write exploit code. 5. Much of the tracing infrastructure allows access to user registers. I have not attempted to determine which forms of tracing allow access to user registers without already allowing access to kernel registers. Fixes: 7db91e57a0ac ("RISC-V: Task implementation") Cc: stable@vger.kernel.org Signed-off-by: Stefan O'Rear Reviewed-by: Alexandre Ghiti Link: https://lore.kernel.org/r/20240327061258.2370291-1-sorear@fastmail.com Signed-off-by: Palmer Dabbelt Signed-off-by: Greg Kroah-Hartman --- arch/riscv/kernel/process.c | 3 --- 1 file changed, 3 deletions(-) --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -27,8 +27,6 @@ #include #include -register unsigned long gp_in_global __asm__("gp"); - #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_STACKPROTECTOR_PER_TASK) #include unsigned long __stack_chk_guard __read_mostly; @@ -207,7 +205,6 @@ int copy_thread(struct task_struct *p, c if (unlikely(args->fn)) { /* Kernel thread */ memset(childregs, 0, sizeof(struct pt_regs)); - childregs->gp = gp_in_global; /* Supervisor/Machine, irqs on: */ childregs->status = SR_PP | SR_PIE;