From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 0B9143858D32 for ; Tue, 26 Jul 2022 11:06:38 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 0B9143858D32 Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-272-aLGBITHRNXKWI2wEyPYLVQ-1; Tue, 26 Jul 2022 07:06:34 -0400 X-MC-Unique: aLGBITHRNXKWI2wEyPYLVQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 019B23C22880; Tue, 26 Jul 2022 11:06:34 +0000 (UTC) Received: from oldenburg.str.redhat.com (unknown [10.39.193.56]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2A296401473; Tue, 26 Jul 2022 11:06:32 +0000 (UTC) From: Florian Weimer To: "Jason A. Donenfeld" Cc: Mark Harris , libc-alpha@sourceware.org, linux-crypto@vger.kernel.org Subject: Re: [PATCH v2] arc4random: simplify design for better safety References: <20220725225728.824128-1-Jason@zx2c4.com> <20220725232810.843433-1-Jason@zx2c4.com> Date: Tue, 26 Jul 2022 13:06:31 +0200 In-Reply-To: (Jason A. Donenfeld's message of "Tue, 26 Jul 2022 12:41:13 +0200") Message-ID: <87bktci154.fsf@oldenburg.str.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 X-Spam-Status: No, score=-5.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_NONE, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Jul 2022 11:06:39 -0000 * Jason A. Donenfeld: > Not in current kernels, where it always returns at least PAGE_SIZE bytes > before checking for pending signals. In older kernels, if there was a > signal pending at the top, it would do no work and return -ERESTARTSYS, > which I believe should then get restarted by glibc's syscaller? glibc does not handle ERESTARTSYS, it's a kernel-internal error code that's not exported in UAPI headers and must not leak to userspace (except perhaps via ptrace). I believe restarts are handled in the kernel signal code, by tweaking the program counter. Looking at that, ERESTARTSYS gets translated to EINTR for !SA_RESTART system calls: /* Are we from a system call? */ if (syscall_get_nr(current, regs) != -1) { /* If so, check system call restarting.. */ switch (syscall_get_error(current, regs)) { case -ERESTART_RESTARTBLOCK: case -ERESTARTNOHAND: regs->ax = -EINTR; break; case -ERESTARTSYS: if (!(ksig->ka.sa.sa_flags & SA_RESTART)) { regs->ax = -EINTR; break; } fallthrough; case -ERESTARTNOINTR: regs->ax = regs->orig_ax; regs->ip -= 2; break; } } (arch/x86/kernel/signal.c) Thanks, Florian