Reapply "[sanitizer_common] AND signals in BlockSignals instead of deleting (llvm#113443)" for non-Android Linux only (llvm#115790)

The original patch (25fd366) was
reverted in 083a5cd because it broke
some buildbots.

This revised patch makes two changes:
- Reverts to *pre-llvm#98200* behavior for Android. This avoids a build
breakage on Android.
- Only define KeepUnblocked if SANITIZER_LINUX: this avoids a build
breakage on solaris, which does not support internal_sigdelset.
N.B. Other buildbot failures were non-sanitizer tests and are therefore
unrelated.

Original commit message:
    My earlier patch llvm#98200
    caused a regression because it unconditionally unblocked synchronous
    signals, even if the user program had deliberately blocked them.
    This patch fixes the issue by checking the current signal mask, as
    suggested by Vitaly. It also adds tests.
    Fixes llvm#113385

Author: thurstond

Diff for: compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp

@@ -164,33 +164,56 @@ void SetSigProcMask(__sanitizer_sigset_t *set, __sanitizer_sigset_t *oldset) {
   CHECK_EQ(0, internal_sigprocmask(SIG_SETMASK, set, oldset));
 }
 
+#  if SANITIZER_LINUX
+// Deletes the specified signal from newset, if it is not present in oldset
+// Equivalently: newset[signum] = newset[signum] & oldset[signum]
+static void KeepUnblocked(__sanitizer_sigset_t &newset,
+                          __sanitizer_sigset_t &oldset, int signum) {
+  // FIXME: https://github.com/google/sanitizers/issues/1816
+  if (SANITIZER_ANDROID || !internal_sigismember(&oldset, signum))
+    internal_sigdelset(&newset, signum);
+}
+#  endif
+
 // Block asynchronous signals
 void BlockSignals(__sanitizer_sigset_t *oldset) {
-  __sanitizer_sigset_t set;
-  internal_sigfillset(&set);
-#  if SANITIZER_LINUX && !SANITIZER_ANDROID
+  __sanitizer_sigset_t newset;
+  internal_sigfillset(&newset);
+
+#  if SANITIZER_LINUX
+  __sanitizer_sigset_t currentset;
+
+#    if !SANITIZER_ANDROID
+  // FIXME: https://github.com/google/sanitizers/issues/1816
+  SetSigProcMask(NULL, &currentset);
+
   // Glibc uses SIGSETXID signal during setuid call. If this signal is blocked
   // on any thread, setuid call hangs.
   // See test/sanitizer_common/TestCases/Linux/setuid.c.
-  internal_sigdelset(&set, 33);
-#  endif
-#  if SANITIZER_LINUX
+  KeepUnblocked(newset, currentset, 33);
+#    endif  // !SANITIZER_ANDROID
+
   // Seccomp-BPF-sandboxed processes rely on SIGSYS to handle trapped syscalls.
   // If this signal is blocked, such calls cannot be handled and the process may
   // hang.
-  internal_sigdelset(&set, 31);
+  KeepUnblocked(newset, currentset, 31);
 
+#    if !SANITIZER_ANDROID
   // Don't block synchronous signals
-  internal_sigdelset(&set, SIGSEGV);
-  internal_sigdelset(&set, SIGBUS);
-  internal_sigdelset(&set, SIGILL);
-  internal_sigdelset(&set, SIGTRAP);
-  internal_sigdelset(&set, SIGABRT);
-  internal_sigdelset(&set, SIGFPE);
-  internal_sigdelset(&set, SIGPIPE);
-#  endif
+  // but also don't unblock signals that the user had deliberately blocked.
+  // FIXME: https://github.com/google/sanitizers/issues/1816
+  KeepUnblocked(newset, currentset, SIGSEGV);
+  KeepUnblocked(newset, currentset, SIGBUS);
+  KeepUnblocked(newset, currentset, SIGILL);
+  KeepUnblocked(newset, currentset, SIGTRAP);
+  KeepUnblocked(newset, currentset, SIGABRT);
+  KeepUnblocked(newset, currentset, SIGFPE);
+  KeepUnblocked(newset, currentset, SIGPIPE);
+#    endif  //! SANITIZER_ANDROID
+
+#  endif  // SANITIZER_LINUX
 
-  SetSigProcMask(&set, oldset);
+  SetSigProcMask(&newset, oldset);
 }
 
 ScopedBlockSignals::ScopedBlockSignals(__sanitizer_sigset_t *copy) {

Diff for: compiler-rt/lib/sanitizer_common/tests/CMakeLists.txt

@@ -15,6 +15,7 @@ set(SANITIZER_UNITTESTS
   sanitizer_array_ref_test.cpp
   sanitizer_atomic_test.cpp
   sanitizer_bitvector_test.cpp
+  sanitizer_block_signals.cpp
   sanitizer_bvgraph_test.cpp
   sanitizer_chained_origin_depot_test.cpp
   sanitizer_common_test.cpp

Diff for: compiler-rt/lib/sanitizer_common/tests/sanitizer_block_signals.cpp

@@ -0,0 +1,76 @@
+//===-- sanitizer_block_signals.cpp ---------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file is a part of sanitizer_common unit tests.
+//
+//===----------------------------------------------------------------------===//
+#include <signal.h>
+#include <stdio.h>
+
+#include "gtest/gtest.h"
+#include "sanitizer_common/sanitizer_linux.h"
+
+namespace __sanitizer {
+
+#if SANITIZER_LINUX && !SANITIZER_ANDROID
+volatile int received_sig = -1;
+
+void signal_handler(int signum) { received_sig = signum; }
+
+TEST(SanitizerCommon, NoBlockSignals) {
+  // No signals blocked
+  signal(SIGUSR1, signal_handler);
+  raise(SIGUSR1);
+  EXPECT_EQ(received_sig, SIGUSR1);
+
+  received_sig = -1;
+  signal(SIGPIPE, signal_handler);
+  raise(SIGPIPE);
+  EXPECT_EQ(received_sig, SIGPIPE);
+}
+
+TEST(SanitizerCommon, BlockSignalsPlain) {
+  // ScopedBlockSignals; SIGUSR1 should be blocked but not SIGPIPE
+  {
+    __sanitizer_sigset_t sigset = {};
+    ScopedBlockSignals block(&sigset);
+
+    received_sig = -1;
+    signal(SIGUSR1, signal_handler);
+    raise(SIGUSR1);
+    EXPECT_EQ(received_sig, -1);
+
+    received_sig = -1;
+    signal(SIGPIPE, signal_handler);
+    raise(SIGPIPE);
+    EXPECT_EQ(received_sig, SIGPIPE);
+  }
+  EXPECT_EQ(received_sig, SIGUSR1);
+}
+
+TEST(SanitizerCommon, BlockSignalsExceptPipe) {
+  // Manually block SIGPIPE; ScopedBlockSignals should not unblock this
+  sigset_t block_sigset;
+  sigemptyset(&block_sigset);
+  sigaddset(&block_sigset, SIGPIPE);
+  sigprocmask(SIG_BLOCK, &block_sigset, NULL);
+  {
+    __sanitizer_sigset_t sigset = {};
+    ScopedBlockSignals block(&sigset);
+
+    received_sig = -1;
+    signal(SIGPIPE, signal_handler);
+    raise(SIGPIPE);
+    EXPECT_EQ(received_sig, -1);
+  }
+  sigprocmask(SIG_UNBLOCK, &block_sigset, NULL);
+  EXPECT_EQ(received_sig, SIGPIPE);
+}
+#endif  // SANITIZER_LINUX && !SANITIZER_ANDROID
+
+}  // namespace __sanitizer