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 lists.gnu.org (lists.gnu.org [209.51.188.17]) (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 436E5C433EF for ; Thu, 27 Jan 2022 22:49:01 +0000 (UTC) Received: from localhost ([::1]:39964 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nDDZb-0004rK-Qf for qemu-devel@archiver.kernel.org; Thu, 27 Jan 2022 17:48:59 -0500 Received: from eggs.gnu.org ([209.51.188.92]:54120) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nDDXP-0003dE-QY for qemu-devel@nongnu.org; Thu, 27 Jan 2022 17:46:44 -0500 Received: from [2607:f8b0:4864:20::634] (port=36704 helo=mail-pl1-x634.google.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.90_1) (envelope-from ) id 1nDDXN-0004HU-81 for qemu-devel@nongnu.org; Thu, 27 Jan 2022 17:46:43 -0500 Received: by mail-pl1-x634.google.com with SMTP id b15so4178574plg.3 for ; Thu, 27 Jan 2022 14:46:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bsdimp-com.20210112.gappssmtp.com; s=20210112; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=s3veLufp/yiLhnxXtFWoUZqDxFnJjzSB4DAkx0e5JK4=; b=TyhiR6wj1Fq8WKGaSpyu+p1z5ny46KDx/z/k985C6GG8TrPgSI7H/IpGCzy/E3nEIu 19MKJXzS7nB4CtBZqAjJZySvvIxZ87dEWDEBHTGZNk2YrgF4vKFxdomKxebZEzzxcnUh ntIAib+/k/twIr6ilNsYOFYvGfzafFLrhdg/9VV/u5VY9ym8pW1qrqr8unzt240vIX6M JBvS6fJ8q3xlhXYTB1RJeDidyY+0WPmiN3VP3PlcpKAW74ZbNXUeqVizrTg3bfLa/z0o UCp5xRZ7jnXkvs4Q/TNBHvZyijBxuihMvx8MUj0TceNdDY9obSx+11NLS2ncqlKbWZtv O+fA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=s3veLufp/yiLhnxXtFWoUZqDxFnJjzSB4DAkx0e5JK4=; b=nErpZI59e1GsaSRkJ0XBfCPYdBN9EE+HtkBTVEqtttZYVYYpmGSDXfbS53LBYWxcmO 6IOTd3RFW9KpqGb0CF0uXKOzdxA1x17JqxRN3aUuH0Py7tFPGF3E6EjruEm+WNfOEJfM B/tWX5PXRzrSQlCmVNi0jEZCi4GPhW5pSumSShBVtZuFD8r95Mz9f9TofbJlXk9BR9cu SgEQUBpQa9E96yQj7D4nzT3NbrSGs0t8GAJRfI2RasVbeBcJ64kfZRCZK8fMgDHD+ijp UYwt453F4+M3kpGejI9DVNJEO6guBqyzJb/MEixhijIHFG+x+OIpAeZrJe2ApFVT6ZeU e6Ig== X-Gm-Message-State: AOAM530P8pEZVp27wUPyrVPmtDm2bmqBHq1Wn3p0ZyRTBMaFkCqIAp7D LoMabxvI1T+ukDEck10YK9Ou+g== X-Google-Smtp-Source: ABdhPJxw1djos04ICsSfStmMpLKB9mz5i2sQOdIR1qz82AiTX8Is1AswE6C3WMaNGz/HzFw2/ctxqg== X-Received: by 2002:a17:902:dac3:: with SMTP id q3mr5310350plx.161.1643323599270; Thu, 27 Jan 2022 14:46:39 -0800 (PST) Received: from smtpclient.apple ([2603:300b:6:5100:9cd4:545b:aed0:18bd]) by smtp.gmail.com with ESMTPSA id l10sm6390033pff.44.2022.01.27.14.46.37 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 27 Jan 2022 14:46:38 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 15.0 \(3693.40.0.1.81\)) Subject: Re: [PATCH v2 36/40] bsd-user/signal.c: implement do_sigaction From: Warner Losh In-Reply-To: <20220125012947.14974-37-imp@bsdimp.com> Date: Thu, 27 Jan 2022 15:46:36 -0700 Content-Transfer-Encoding: quoted-printable Message-Id: References: <20220125012947.14974-1-imp@bsdimp.com> <20220125012947.14974-37-imp@bsdimp.com> To: Warner Losh X-Mailer: Apple Mail (2.3693.40.0.1.81) X-Host-Lookup-Failed: Reverse DNS lookup failed for 2607:f8b0:4864:20::634 (failed) Received-SPF: none client-ip=2607:f8b0:4864:20::634; envelope-from=wlosh@bsdimp.com; helo=mail-pl1-x634.google.com X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, PDS_HP_HELO_NORDNS=0.001, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Stacey Son , Kyle Evans , Richard Henderson , QEMU Developers , "def@freebsd.org" , "jrtc27@freebsd.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" > On Jan 24, 2022, at 6:29 PM, Warner Losh wrote: >=20 > Implement the meat of the sigaction(2) system call with do_sigaction = and > helper routiner block_signals (which is also used to implemement = signal > masking so it's global). >=20 > Signed-off-by: Stacey Son > Signed-off-by: Kyle Evans > Signed-off-by: Warner Losh >=20 > Pending Comments from Peter Maydell >=20 > (1) in block_signals, sigprocmast > For linux-user we rely on sigprocmask() in a multithreaded > program setting the signal mask for only the calling thread, > which isn't POSIX-mandated. (Arguably we should use > pthread_sigmask() instead, but we don't for basically > historical reasons since linux-user is host-OS-specific anyway.) > Does BSD have the same "this changes this thread's signal mask" > semantics for sigprocmask()? FreeBSD changes this on a per-thread basis for both sigprocmask and pthread_sigmask(). pthread_sigmask() just does some extra stuff with SIGCANCEL for pthread_cancel support which qemu doesn=E2=80=99t use. They are the same. I=E2=80=99m = inclined to leave it as sigprocmask() since I=E2=80=99m unsure what the = implications of doing funky things for SIGCANCEL would be. > (2) do_sigaction, first if validating which signals can be sent > Kernel seems to allow SIGKILL and SIGSTOP unless act is > non-NULL and act->sa_handler is SIG_DFL ? > = https://github.com/freebsd/freebsd-src/blob/main/sys/kern/kern_sig.c#L747 > (Compare linux-user commit ee3500d33a7431, a recent bugfix.) That fix is relevant, so I=E2=80=99ll bring that in. Thanks! > (3) Noting confusion in do_sigaction between host and target > errnos (they are identical on BSD, but we should still return > the right sort in case it ever does matter). Will fix before V3 of patches. Warner > --- > bsd-user/signal-common.h | 22 ++++++++++++ > bsd-user/signal.c | 76 ++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 98 insertions(+) >=20 > diff --git a/bsd-user/signal-common.h b/bsd-user/signal-common.h > index 786ec592d18..7ff8e8f2e40 100644 > --- a/bsd-user/signal-common.h > +++ b/bsd-user/signal-common.h > @@ -9,7 +9,29 @@ > #ifndef SIGNAL_COMMON_H > #define SIGNAL_COMMON_H >=20 > +/** > + * block_signals: block all signals while handling this guest syscall > + * > + * Block all signals, and arrange that the signal mask is returned to > + * its correct value for the guest before we resume execution of = guest code. > + * If this function returns non-zero, then the caller should = immediately > + * return -TARGET_ERESTARTSYS to the main loop, which will take the = pending > + * signal and restart execution of the syscall. > + * If block_signals() returns zero, then the caller can continue with > + * emulation of the system call knowing that no signals can be taken > + * (and therefore that no race conditions will result). > + * This should only be called once, because if it is called a second = time > + * it will always return non-zero. (Think of it like a mutex that = can't > + * be recursively locked.) > + * Signals will be unblocked again by process_pending_signals(). > + * > + * Return value: non-zero if there was a pending signal, zero if not. > + */ > +int block_signals(void); /* Returns non zero if signal pending */ > + > long do_rt_sigreturn(CPUArchState *env); > +int do_sigaction(int sig, const struct target_sigaction *act, > + struct target_sigaction *oact); > abi_long do_sigaltstack(abi_ulong uss_addr, abi_ulong uoss_addr, = abi_ulong sp); > long do_sigreturn(CPUArchState *env, abi_ulong addr); > void force_sig_fault(int sig, int code, abi_ulong addr); > diff --git a/bsd-user/signal.c b/bsd-user/signal.c > index 05caf812ccb..42021556d65 100644 > --- a/bsd-user/signal.c > +++ b/bsd-user/signal.c > @@ -309,6 +309,22 @@ static void tswap_siginfo(target_siginfo_t = *tinfo, const target_siginfo_t *info) > } > } >=20 > +int block_signals(void) > +{ > + TaskState *ts =3D (TaskState *)thread_cpu->opaque; > + sigset_t set; > + > + /* > + * It's OK to block everything including SIGSEGV, because we = won't run any > + * further guest code before unblocking signals in > + * process_pending_signals(). > + */ > + sigfillset(&set); > + sigprocmask(SIG_SETMASK, &set, 0); > + > + return qatomic_xchg(&ts->signal_pending, 1); > +} > + > /* Returns 1 if given signal should dump core if not handled. */ > static int core_dump_signal(int sig) > { > @@ -554,6 +570,66 @@ static void host_signal_handler(int host_sig, = siginfo_t *info, void *puc) > cpu_exit(thread_cpu); > } >=20 > +/* do_sigaction() return host values and errnos */ > +int do_sigaction(int sig, const struct target_sigaction *act, > + struct target_sigaction *oact) > +{ > + struct target_sigaction *k; > + struct sigaction act1; > + int host_sig; > + int ret =3D 0; > + > + if (sig < 1 || sig > TARGET_NSIG || sig =3D=3D TARGET_SIGKILL || > + sig =3D=3D TARGET_SIGSTOP) { > + return -EINVAL; > + } > + > + if (block_signals()) { > + return -TARGET_ERESTART; > + } > + > + k =3D &sigact_table[sig - 1]; > + if (oact) { > + oact->_sa_handler =3D tswapal(k->_sa_handler); > + oact->sa_flags =3D tswap32(k->sa_flags); > + oact->sa_mask =3D k->sa_mask; > + } > + if (act) { > + /* XXX: this is most likely not threadsafe. */ > + k->_sa_handler =3D tswapal(act->_sa_handler); > + k->sa_flags =3D tswap32(act->sa_flags); > + k->sa_mask =3D act->sa_mask; > + > + /* Update the host signal state. */ > + host_sig =3D target_to_host_signal(sig); > + if (host_sig !=3D SIGSEGV && host_sig !=3D SIGBUS) { > + memset(&act1, 0, sizeof(struct sigaction)); > + sigfillset(&act1.sa_mask); > + act1.sa_flags =3D SA_SIGINFO; > + if (k->sa_flags & TARGET_SA_RESTART) { > + act1.sa_flags |=3D SA_RESTART; > + } > + /* > + * Note: It is important to update the host kernel = signal mask to > + * avoid getting unexpected interrupted system calls. > + */ > + if (k->_sa_handler =3D=3D TARGET_SIG_IGN) { > + act1.sa_sigaction =3D (void *)SIG_IGN; > + } else if (k->_sa_handler =3D=3D TARGET_SIG_DFL) { > + if (fatal_signal(sig)) { > + act1.sa_sigaction =3D host_signal_handler; > + } else { > + act1.sa_sigaction =3D (void *)SIG_DFL; > + } > + } else { > + act1.sa_sigaction =3D host_signal_handler; > + } > + ret =3D sigaction(host_sig, &act1, NULL); > + } > + } > + return ret; > +} > + > static inline abi_ulong get_sigframe(struct target_sigaction *ka, > CPUArchState *env, size_t frame_size) > { > --=20 > 2.33.1 >=20