From mboxrd@z Thu Jan 1 00:00:00 1970 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D36EDC4451B for ; Fri, 17 Jul 2026 18:28:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:Message-ID:Date:Subject:Cc:To:From:Reply-To:Content-Type: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=KmmHwwXhoxMf1LiiZHXzEaId8Hd79DsFFZARM3V2GZU=; b=LLvx0vZ8WOcKHcXgi10mnRjUD8 CQskS+F4PnriKZtEwwS+iVGKQlJ2UoLfdrLAqZSJYi9duuAGAwVmqhQz1dc2mN8YNQa7xbZZC3LzF IUNVfaSAi79ojzeswRVdRviep3WK/rWC3skoPD7pnxNl+s5YUn5Qr9iEZUW+slTz+QUiIIudnSbMJ 2cXJuVtzw5SnQlyysP7YG/31vcc8PqlDUGzfu0B6rsbjw9nav/FbZfE0oYk77Q9qbc55dk/RsP4Ka OLixLkSEH6xcK1qB1s+5mkByuHjlGUGJbTAVlNKX1EdjhqQ3cSv0xMLfq/dRoQR63LJpcrFa0aL5T sI4pTJeQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wknIB-000000031Kg-2Wjt; Fri, 17 Jul 2026 18:28:11 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wknIA-000000031KH-02m3 for linux-arm-kernel@lists.infradead.org; Fri, 17 Jul 2026 18:28:10 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 60BE760A74; Fri, 17 Jul 2026 18:28:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9A0DE1F00A3D; Fri, 17 Jul 2026 18:28:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784312889; bh=KmmHwwXhoxMf1LiiZHXzEaId8Hd79DsFFZARM3V2GZU=; h=From:To:Cc:Subject:Date; b=GTPsVIlQpzR8R2i7oNr0zumdLVzCgrjgCjnOIkeb67312R9oEWVLqxBaiUFPi+7jo JsiKxBBPnfUYWez6rgw/ROSo1Q4lfv83Z2cnOcCCADgho3WCLbSSGLtPHe4pWNFc4l 0KmWe/uEzhNyQh+cd0ECoit/Veo1u1peytM2fKog8e+mCT7RFngb1H7cgd3pIFNlGM REGy/xsz2WTHzdWgCPYMPCnaLRRErV9LqmAZO+H3QPn/uwUwt6d4PUr7YDFYGc0SNB IC16DB+Dh9+r3QdSh6ZkHaCEhljOplFs13Fo1GHEKQuBTqZtp4U6oSis2tnnfml8er y9ROaGgYoW2hw== From: Will Deacon To: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org, Will Deacon , Kees Cook , Jinjie Ruan , Mark Rutland , Yiqi Sun Subject: [PATCH v3] arm64: ptrace: Keep 'orig_x0' in-sync with x0 on syscall entry Date: Fri, 17 Jul 2026 19:27:58 +0100 Message-ID: <20260717182758.17111-1-will@kernel.org> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Commit e057b9477232 ("arm64: syscall: Ensure saved x0 is kept in-sync with tracer updates") attempted to resolve a long-standing issue with syscall entry tracing, where a tracer is able to manipulate the first syscall argument without being subjected to seccomp or audit checking. Unfortunately, that fix was incomplete [1], as it failed to update 'orig_x0' between a tracer updating x0 during a seccomp ptrace exit (SECCOMP_RET_TRACE) and the seccomp filter being re-evaluated. Rather than add hooks to the core seccomp code, instead move the synchronisation code into the ptrace GPR and syscall setting code so that 'orig_x0' is kept up to date with x0 whenever we're stopped on the syscall entry path. Cc: Kees Cook Cc: Jinjie Ruan Cc: Mark Rutland Link: https://sashiko.dev/#/patchset/20260716120640.6590-1-will@kernel.org [1] Reported-by: Yiqi Sun Link: https://lore.kernel.org/all/20260529065444.1336608-1-sunyiqixm@gmail.com/ Fixes: e057b9477232 ("arm64: syscall: Ensure saved x0 is kept in-sync with tracer updates") Fixes: a5cd110cb836 ("arm64/ptrace: run seccomp after ptrace") Signed-off-by: Will Deacon --- arch/arm64/kernel/ptrace.c | 50 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+) v2: https://lore.kernel.org/r/20260716120640.6590-1-will@kernel.org diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c index 4d08598e2891..2b716fa11c02 100644 --- a/arch/arm64/kernel/ptrace.c +++ b/arch/arm64/kernel/ptrace.c @@ -560,6 +560,42 @@ static int gpr_get(struct task_struct *target, return membuf_write(&to, uregs, sizeof(*uregs)); } +static void update_syscall_orig_x0_after_ptrace(struct task_struct *target) +{ + struct pt_regs *regs = task_pt_regs(target); + struct kernel_siginfo *info = target->last_siginfo; + + /* We should only be called when target is in a ptrace stop */ + if (WARN_ON_ONCE(!info)) + return; + + /* + * Skip the update for NO_SYSCALL (set either by the user or the + * tracer), as regs[0] holds the return value (see the comment in + * el0_svc_common()) and can be unwound using syscall_rollback(). + */ + if (regs->syscallno == NO_SYSCALL) + return; + + /* + * For compat tasks, orig_r0 is provided directly through GPR index + * 17. + */ + if (is_compat_thread(task_thread_info(target))) + return; + + /* + * Don't update orig_x0 for a syscall-exit-stop, as x0 now contains the + * return value of the system call. + */ + if ((info->si_code & ~0x80) == SIGTRAP && + target->ptrace_message == PTRACE_EVENTMSG_SYSCALL_EXIT) { + return; + } + + regs->orig_x0 = regs->regs[0]; +} + static int gpr_set(struct task_struct *target, const struct user_regset *regset, unsigned int pos, unsigned int count, const void *kbuf, const void __user *ubuf) @@ -575,6 +611,14 @@ static int gpr_set(struct task_struct *target, const struct user_regset *regset, return -EINVAL; task_pt_regs(target)->user_regs = newregs; + + /* + * Keep orig_x0 authoritative so that seccomp (via + * syscall_get_arguments()), audit and the restart path all see the same + * first argument the syscall is dispatched with, even if it has been + * updated by a tracer. + */ + update_syscall_orig_x0_after_ptrace(target); return 0; } @@ -753,6 +797,12 @@ static int system_call_set(struct task_struct *target, return ret; task_pt_regs(target)->syscallno = syscallno; + + /* + * Re-sync orig_x0 in case the syscall number has been changed + * from NO_SYSCALL. + */ + update_syscall_orig_x0_after_ptrace(target); return ret; } -- 2.55.0.229.g6434b31f56-goog