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 743DC524AD for ; Mon, 8 Apr 2024 10:16:21 +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=1712571381; cv=none; b=OGziiJzm9MtJJfLIiQNsagNQp/HIoUDWjkHz8csymMq+SYjPoelEiEVCFvNU2dmSp61X7jwHdvOKh12+dp4kyrST/GyWY8nnIxfE43zTx9FbFja/GXnMh4YLj8d1bIymLlw1SPJNZpzPNt3UviGKpEQMPHUpWXskFVn6YZkkpAA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712571381; c=relaxed/simple; bh=g0ah6wefcAMZGeJeZTrgzwKbcBE92kjqivg6ijC+cu8=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=HQdsOY26jJ8kIiEQHLphmEg1YMxBTe3eXNba9yyYSABreVEdMUpcWUiNXvTa76Wq6UCQJf/CTSArBKLa7MwBPsC5xA2iCIrsP4/tjgK+0K7O+o3bEXkVk1/7TYB2IidUQsKI+8/V9v96imuWu9pfRdfZ7+8ir6JpfXZnHmzu7UY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=SQXrd99f; 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="SQXrd99f" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DCB6EC433C7; Mon, 8 Apr 2024 10:16:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1712571381; bh=g0ah6wefcAMZGeJeZTrgzwKbcBE92kjqivg6ijC+cu8=; h=Subject:To:Cc:From:Date:From; b=SQXrd99fLuixE/smSTEATjPJFzwbDDZ8Tx9NVUTEioQA1mR1jQiYWwgx+ow5C0x73 r6ZtG+ADm/7XTJMjlNN7Uc8AQr5Sm3qcBVYMoZBUxpIju2tivgXNzp7ebYkgqAk85r rWhYUvX3oW29SHUxl9uecAuWt7gQ0k4UNzTFYhCw= Subject: FAILED: patch "[PATCH] riscv: process: Fix kernel gp leakage" failed to apply to 5.4-stable tree To: sorear@fastmail.com,alexghiti@rivosinc.com,palmer@rivosinc.com Cc: From: Date: Mon, 08 Apr 2024 12:16:15 +0200 Message-ID: <2024040815-geometric-quaintly-f4a7@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y git checkout FETCH_HEAD git cherry-pick -x d14fa1fcf69db9d070e75f1c4425211fa619dfc8 # git commit -s git send-email --to '' --in-reply-to '2024040815-geometric-quaintly-f4a7@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^.. Possible dependencies: d14fa1fcf69d ("riscv: process: Fix kernel gp leakage") fea2fed201ee ("riscv: Enable per-task stack canaries") d7071743db31 ("RISC-V: Add EFI stub support.") f2c9699f6555 ("riscv: Add STACKPROTECTOR supported") a5d8e55b2c7d ("Merge tag 'v5.7-rc7' into efi/core, to refresh the branch and pick up fixes") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From d14fa1fcf69db9d070e75f1c4425211fa619dfc8 Mon Sep 17 00:00:00 2001 From: Stefan O'Rear Date: Wed, 27 Mar 2024 02:12:58 -0400 Subject: [PATCH] riscv: process: Fix kernel gp leakage 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 diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index 6abeecbfc51d..e4bc61c4e58a 100644 --- 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, const struct kernel_clone_args *args) 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;