support: add check_mem_access function

Add check_mem_access(addr) function to check if memory at addr can
be written or read returning false if memory is not accessible.

This function changes signal handler for SIGSEGV and SIGBUS signals
when it is called first, and it is not thread-safe.

Co-authored-by: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

diff --git a/include/setjmp.h b/include/setjmp.h
index d2353be71bdc196f7b9097c107ec7bf544f93951..4997d0d7d217873cbcd41f403cd3d9f19a536967 100644 (file)
--- a/include/setjmp.h
+++ b/include/setjmp.h
@@ -12,7 +12,7 @@ extern void ____longjmp_chk (__jmp_buf __env, int __val)
      __attribute__ ((__noreturn__)) attribute_hidden;
 
 extern void __longjmp_chk (sigjmp_buf env, int val)
-         __attribute__ ((noreturn)) attribute_hidden;
+         __attribute__ ((noreturn));
 /* The redirection in the installed header does not work with
    libc_hidden_proto.  */
 #define longjmp __longjmp_chk

diff --git a/nptl/tst-guard1.c b/nptl/tst-guard1.c
index e3e06df0fc91dd59f3f1df74aed777a435915f2d..6732b090171bdc51c6f76708778fb2d03cf709ea 100644 (file)
--- a/nptl/tst-guard1.c
+++ b/nptl/tst-guard1.c
@@ -26,54 +26,22 @@
 #include <support/xsignal.h>
 #include <support/xthread.h>
 #include <support/xunistd.h>
+#include <support/check_mem_access.h>
 #include <sys/mman.h>
 #include <stdlib.h>
 
 static long int pagesz;
 
-/* To check if the guard region is inaccessible, the thread tries read/writes
-   on it and checks if a SIGSEGV is generated.  */
-
-static volatile sig_atomic_t signal_jump_set;
-static sigjmp_buf signal_jmp_buf;
-
-static void
-sigsegv_handler (int sig)
-{
-  if (signal_jump_set == 0)
-    return;
-
-  siglongjmp (signal_jmp_buf, sig);
-}
-
-static bool
-try_access_buf (char *ptr, bool write)
-{
-  signal_jump_set = true;
-
-  bool failed = sigsetjmp (signal_jmp_buf, 0) != 0;
-  if (!failed)
-    {
-      if (write)
-       *(volatile char *)(ptr) = 'x';
-      else
-       *(volatile char *)(ptr);
-    }
-
-  signal_jump_set = false;
-  return !failed;
-}
-
 static bool
 try_read_buf (char *ptr)
 {
-  return try_access_buf (ptr, false);
+  return check_mem_access (ptr, false);
 }
 
 static bool
 try_write_buf (char *ptr)
 {
-  return try_access_buf (ptr, true);
+  return check_mem_access (ptr, true);
 }
 
 static bool
@@ -332,18 +300,6 @@ do_test (void)
 {
   pagesz = sysconf (_SC_PAGESIZE);
 
-  {
-    struct sigaction sa = {
-      .sa_handler = sigsegv_handler,
-      .sa_flags = SA_NODEFER,
-    };
-    sigemptyset (&sa.sa_mask);
-    xsigaction (SIGSEGV, &sa, NULL);
-    /* Some system generates SIGBUS accessing the guard area when it is
-       setup with madvise.  */
-    xsigaction (SIGBUS, &sa, NULL);
-  }
-
   static const struct {
     const char *descr;
     void (*test)(void);

diff --git a/support/Makefile b/support/Makefile
index f67f38130a2ff77d0ddab2e4dec89af52ff5cd77..f0a1e1ca444dc5132dc55880cfe83899d2427d46 100644 (file)
--- a/support/Makefile
+++ b/support/Makefile
@@ -66,6 +66,7 @@ libsupport-routines = \
   support_format_netent \
   support_fuse \
   support_isolate_in_subprocess \
+  support_mem_access \
   support_mutex_pi_monotonic \
   support_need_proc \
   support_open_and_compare_file_bytes \

diff --git a/support/check_mem_access.h b/support/check_mem_access.h
new file mode 100644 (file)
index 0000000..116e1f7
--- /dev/null
+++ b/support/check_mem_access.h
@@ -0,0 +1,36 @@
+/* Test verification functions for memory access checks.
+   Copyright (C) 2025 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef SUPPORT_CHECK_MEM_ACCESS_H
+#define SUPPORT_CHECK_MEM_ACCESS_H
+
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+/* To check if the a memory region is inaccessible, this function tries
+   read / write on the provided address ADDR and checks if a SIGSEGV is
+   generated.  This function is not thread-safe and it changes signal
+   handlers for SIGSEGV and SIGBUS.
+   If WRITE is true, only the write operation is checked, otherwise only
+   the read operation is checked. */
+bool check_mem_access (const void *addr, bool write);
+
+__END_DECLS
+
+#endif // SUPPORT_CHECK_MEM_ACCESS_H

diff --git a/support/support_mem_access.c b/support/support_mem_access.c
new file mode 100644 (file)
index 0000000..aa5127b
--- /dev/null
+++ b/support/support_mem_access.c
@@ -0,0 +1,61 @@
+/* Implementation of the test verification functions for memory access
+   checks.
+   Copyright (C) 2025 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <setjmp.h>
+#include <signal.h>
+#include <support/xsignal.h>
+
+static sigjmp_buf sigsegv_jmp_buf;
+
+static void
+__sigsegv_handler (int signum)
+{
+  siglongjmp (sigsegv_jmp_buf, signum);
+}
+
+bool check_mem_access (const void *addr, bool write)
+{
+  /* This is obviously not thread-safe.  */
+  static bool handler_set_up;
+  if (!handler_set_up)
+    {
+      struct sigaction sa = {
+       .sa_handler = __sigsegv_handler,
+       .sa_flags = SA_NODEFER,
+      };
+      sigemptyset (&sa.sa_mask);
+      xsigaction (SIGSEGV, &sa, NULL);
+      /* Some system generates SIGBUS accessing the guard area when it is
+        setup with madvise.  */
+      xsigaction (SIGBUS, &sa, NULL);
+      handler_set_up = true;
+    }
+  int r = sigsetjmp (sigsegv_jmp_buf, 0);
+  if (r == 0)
+    {
+      if (write)
+        *(volatile char *)addr = 'x';
+      else
+        *(volatile char *)addr;
+      return true;
+    }
+  if (r == SIGSEGV || r == SIGBUS)
+    return false;
+  return true;
+}