[PATCH v2 26/40] bsd-user/signal.c: Implement host_signal_handler

[Warner Losh <imp@bsdimp.com>]

Implement host_signal_handler to handle signals generated by the host
and to do safe system calls.

Signed-off-by: Stacey Son <sson@FreeBSD.org>
Signed-off-by: Kyle Evans <kevans@freebsd.org>
Signed-off-by: Warner Losh <imp@bsdimp.com>
---
 bsd-user/signal.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 105 insertions(+)

diff --git a/bsd-user/signal.c b/bsd-user/signal.c
index 454aef2993e..24cf4b1120b 100644
--- a/bsd-user/signal.c
+++ b/bsd-user/signal.c
@@ -223,6 +223,111 @@ void force_sig_fault(int sig, int code, abi_ulong addr)
 
 static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
 {
+    CPUArchState *env = thread_cpu->env_ptr;
+    CPUState *cpu = env_cpu(env);
+    TaskState *ts = cpu->opaque;
+    target_siginfo_t tinfo;
+    ucontext_t *uc = puc;
+    struct emulated_sigtable *k;
+    int guest_sig;
+    uintptr_t pc = 0;
+    bool sync_sig = false;
+
+    /*
+     * Non-spoofed SIGSEGV and SIGBUS are synchronous, and need special
+     * handling wrt signal blocking and unwinding.
+     */
+    if ((host_sig == SIGSEGV || host_sig == SIGBUS) && info->si_code > 0) {
+        MMUAccessType access_type;
+        uintptr_t host_addr;
+        abi_ptr guest_addr;
+        bool is_write;
+
+        host_addr = (uintptr_t)info->si_addr;
+
+        /*
+         * Convert forcefully to guest address space: addresses outside
+         * reserved_va are still valid to report via SEGV_MAPERR.
+         */
+        guest_addr = h2g_nocheck(host_addr);
+
+        pc = host_signal_pc(uc);
+        is_write = host_signal_write(info, uc);
+        access_type = adjust_signal_pc(&pc, is_write);
+
+        if (host_sig == SIGSEGV) {
+            bool maperr = true;
+
+            if (info->si_code == SEGV_ACCERR && h2g_valid(host_addr)) {
+                /* If this was a write to a TB protected page, restart. */
+                if (is_write &&
+                    handle_sigsegv_accerr_write(cpu, &uc->uc_sigmask,
+                                                pc, guest_addr)) {
+                    return;
+                }
+
+                /*
+                 * With reserved_va, the whole address space is PROT_NONE,
+                 * which means that we may get ACCERR when we want MAPERR.
+                 */
+                if (page_get_flags(guest_addr) & PAGE_VALID) {
+                    maperr = false;
+                } else {
+                    info->si_code = SEGV_MAPERR;
+                }
+            }
+
+            sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
+            cpu_loop_exit_sigsegv(cpu, guest_addr, access_type, maperr, pc);
+        } else {
+            sigprocmask(SIG_SETMASK, &uc->uc_sigmask, NULL);
+            if (info->si_code == BUS_ADRALN) {
+                cpu_loop_exit_sigbus(cpu, guest_addr, access_type, pc);
+            }
+        }
+
+        sync_sig = true;
+    }
+
+    /* Get the target signal number. */
+    guest_sig = host_to_target_signal(host_sig);
+    if (guest_sig < 1 || guest_sig > TARGET_NSIG) {
+        return;
+    }
+    trace_user_host_signal(cpu, host_sig, guest_sig);
+
+    host_to_target_siginfo_noswap(&tinfo, info);
+
+    k = &ts->sigtab[guest_sig - 1];
+    k->info = tinfo;
+    k->pending = guest_sig;
+    ts->signal_pending = 1;
+
+    /*
+     * For synchronous signals, unwind the cpu state to the faulting
+     * insn and then exit back to the main loop so that the signal
+     * is delivered immediately.
+     */
+    if (sync_sig) {
+        cpu->exception_index = EXCP_INTERRUPT;
+        cpu_loop_exit_restore(cpu, pc);
+    }
+
+    rewind_if_in_safe_syscall(puc);
+
+    /*
+     * Block host signals until target signal handler entered. We
+     * can't block SIGSEGV or SIGBUS while we're executing guest
+     * code in case the guest code provokes one in the window between
+     * now and it getting out to the main loop. Signals will be
+     * unblocked again in process_pending_signals().
+     */
+    sigfillset(&uc->uc_sigmask);
+    sigdelset(&uc->uc_sigmask, SIGSEGV);
+    sigdelset(&uc->uc_sigmask, SIGBUS);
+
+    /* Interrupt the virtual CPU as soon as possible. */
+    cpu_exit(thread_cpu);
 }
 
 void signal_init(void)
-- 
2.33.1