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[50.253.99.174]) by smtp.gmail.com with ESMTPSA id q14sm2061687ilo.63.2022.01.24.17.30.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 Jan 2022 17:30:29 -0800 (PST) From: Warner Losh To: qemu-devel@nongnu.org Subject: [PATCH v2 36/40] bsd-user/signal.c: implement do_sigaction Date: Mon, 24 Jan 2022 18:29:43 -0700 Message-Id: <20220125012947.14974-37-imp@bsdimp.com> X-Mailer: git-send-email 2.33.1 In-Reply-To: <20220125012947.14974-1-imp@bsdimp.com> References: <20220125012947.14974-1-imp@bsdimp.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Host-Lookup-Failed: Reverse DNS lookup failed for 2607:f8b0:4864:20::d2f (failed) Received-SPF: none client-ip=2607:f8b0:4864:20::d2f; envelope-from=imp@bsdimp.com; helo=mail-io1-xd2f.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 , def@FreeBSD.org, jrtc27@FreeBSD.org, Warner Losh Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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). Signed-off-by: Stacey Son Signed-off-by: Kyle Evans Signed-off-by: Warner Losh Pending Comments from Peter Maydell (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()? (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.) (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). --- bsd-user/signal-common.h | 22 ++++++++++++ bsd-user/signal.c | 76 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 98 insertions(+) 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 +/** + * 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) } } +int block_signals(void) +{ + TaskState *ts = (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); } +/* 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 = 0; + + if (sig < 1 || sig > TARGET_NSIG || sig == TARGET_SIGKILL || + sig == TARGET_SIGSTOP) { + return -EINVAL; + } + + if (block_signals()) { + return -TARGET_ERESTART; + } + + k = &sigact_table[sig - 1]; + if (oact) { + oact->_sa_handler = tswapal(k->_sa_handler); + oact->sa_flags = tswap32(k->sa_flags); + oact->sa_mask = k->sa_mask; + } + if (act) { + /* XXX: this is most likely not threadsafe. */ + k->_sa_handler = tswapal(act->_sa_handler); + k->sa_flags = tswap32(act->sa_flags); + k->sa_mask = act->sa_mask; + + /* Update the host signal state. */ + host_sig = target_to_host_signal(sig); + if (host_sig != SIGSEGV && host_sig != SIGBUS) { + memset(&act1, 0, sizeof(struct sigaction)); + sigfillset(&act1.sa_mask); + act1.sa_flags = SA_SIGINFO; + if (k->sa_flags & TARGET_SA_RESTART) { + act1.sa_flags |= SA_RESTART; + } + /* + * Note: It is important to update the host kernel signal mask to + * avoid getting unexpected interrupted system calls. + */ + if (k->_sa_handler == TARGET_SIG_IGN) { + act1.sa_sigaction = (void *)SIG_IGN; + } else if (k->_sa_handler == TARGET_SIG_DFL) { + if (fatal_signal(sig)) { + act1.sa_sigaction = host_signal_handler; + } else { + act1.sa_sigaction = (void *)SIG_DFL; + } + } else { + act1.sa_sigaction = host_signal_handler; + } + ret = sigaction(host_sig, &act1, NULL); + } + } + return ret; +} + static inline abi_ulong get_sigframe(struct target_sigaction *ka, CPUArchState *env, size_t frame_size) { -- 2.33.1