From 37ea979e5689c7507cf5cd078e7e945be02d5705 Mon Sep 17 00:00:00 2001
From: Rob Bradford <robert.bradford@intel.com>
Date: Mon, 7 Mar 2022 10:42:33 +0000
Subject: [PATCH] main: Use non-threaded signal handler for SIGSYS

Replace the thread for handling SIGSYS with a simple signal handler.
This resolves inconsistent delivery of signals to the SIGSYS thread due
to other threads manipulating the signals.

Tested by removing key syscalls from vCPU and virtio device filters and
observing correct notice.

Fixes: #3811

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
---
 src/main.rs | 39 ++++++++++++++-------------------------
 1 file changed, 14 insertions(+), 25 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 5435c845a..ba4999777 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -13,16 +13,12 @@ use libc::EFD_NONBLOCK;
 use log::LevelFilter;
 use option_parser::OptionParser;
 use seccompiler::SeccompAction;
-use signal_hook::{
-    consts::SIGSYS,
-    iterator::{exfiltrator::WithRawSiginfo, SignalsInfo},
-};
+use signal_hook::consts::SIGSYS;
 use std::env;
 use std::fs::File;
 use std::os::unix::io::{FromRawFd, RawFd};
 use std::sync::mpsc::channel;
 use std::sync::{Arc, Mutex};
-use std::thread;
 use thiserror::Error;
 use vmm::config;
 use vmm_sys_util::eventfd::EventFd;
@@ -495,28 +491,21 @@ fn start_vmm(cmd_arguments: ArgMatches) -> Result<Option<String>, Error> {
         SeccompAction::Trap
     };
 
-    // See https://github.com/rust-lang/libc/issues/716 why we can't get the details from siginfo_t
     if seccomp_action == SeccompAction::Trap {
-        thread::Builder::new()
-            .name("seccomp_signal_handler".to_string())
-            .spawn(move || {
-                for si in SignalsInfo::<WithRawSiginfo>::new(&[SIGSYS])
-                    .unwrap()
-                    .forever()
-                {
-                    /* SYS_SECCOMP */
-                    if si.si_code == 1 {
-                        eprint!(
-                            "\n==== seccomp violation ====\n\
-                            Try running with `strace -ff` to identify the cause and open an issue: \
-                            https://github.com/cloud-hypervisor/cloud-hypervisor/issues/new\n"
-                        );
-
-                        signal_hook::low_level::emulate_default_handler(SIGSYS).unwrap();
-                    }
-                }
+        // SAFETY: We only using signal_hook for managing signals and only execute signal
+        // handler safe functions (writing to stderr) and manipulating signals.
+        unsafe {
+            signal_hook::low_level::register(signal_hook::consts::SIGSYS, || {
+                eprint!(
+                    "\n==== Possible seccomp violation ====\n\
+                Try running with `strace -ff` to identify the cause and open an issue: \
+                https://github.com/cloud-hypervisor/cloud-hypervisor/issues/new\n"
+                );
+                signal_hook::low_level::emulate_default_handler(SIGSYS).unwrap();
             })
-            .unwrap();
+        }
+        .map_err(|e| eprintln!("Error adding SIGSYS signal handler: {}", e))
+        .ok();
     }
 
     // Before we start any threads, mask the signals we'll be