[PATCH v7 035/104] tests/tcg/multiarch/gdbstub/prot-none.py: detect if /proc/self/mem can be used to access PROT_NONE pages

Recently (July 2026), this issue became reproducible on debian stable
with kernel (7.1.3) from backports. I suspect it's a default hardening
of kernel related to recent CVEs.

By tracking error reported, we can see that /proc/self/mem pread from
cpu_memory_rw_debug in accel/tcg/user-exec.c returns an error
(Input/Output error).

Detect this situation directly from our gdb python script, by trying the
same thing from current process. If this operation fails, we can
gracefully skip the test.

Fixes: https://gitlab.com/qemu-project/qemu/-/work_items/3329
Tested-by: Aniket Sahu <[email protected]>
Signed-off-by: Pierrick Bouvier <[email protected]>
---
 tests/tcg/multiarch/gdbstub/prot-none.py | 35 ++++++++++++++++++++++--
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/tests/tcg/multiarch/gdbstub/prot-none.py b/tests/tcg/multiarch/gdbstub/prot-none.py
index e653bc697f6..393626a9798 100644
--- a/tests/tcg/multiarch/gdbstub/prot-none.py
+++ b/tests/tcg/multiarch/gdbstub/prot-none.py
@@ -5,6 +5,8 @@
 SPDX-License-Identifier: GPL-2.0-or-later
 """
 import ctypes
+import ctypes.util
+import mmap
 import os
 from test_gdbstub import gdb_exit, main, report
 
@@ -18,6 +20,34 @@ def probe_proc_self_mem():
     except OSError:
         return False
 
+def probe_proc_self_mem_access_prot_none():
+    libc = ctypes.CDLL(ctypes.util.find_library("c"), use_errno=True)
+    libc.mmap.restype = ctypes.c_void_p
+    libc.mmap.argtypes = [ctypes.c_void_p, ctypes.c_size_t, ctypes.c_int,
+                          ctypes.c_int, ctypes.c_int, ctypes.c_long]
+    size = os.sysconf("SC_PAGESIZE")
+    # mmap a PROT_NONE page
+    PROT_NONE = 0
+    addr = libc.mmap(None, size, PROT_NONE,
+                     mmap.MAP_PRIVATE | mmap.MAP_ANONYMOUS, -1, 0)
+    assert addr != ctypes.c_void_p(-1).value
+    fd = os.open("/proc/self/mem", os.O_RDWR)
+    try:
+        # read it through /proc/self/mem
+        data = os.pread(fd, size, addr)
+    except Exception as e:
+        print("/proc/self/mem pread error: " + str(e))
+        return False
+
+    try:
+        # write it through /proc/self/mem
+        os.pwrite(fd, data, addr)
+    except Exception as e:
+        print("/proc/self/mem pwrite error: " + str(e))
+        return False
+
+    return True
+
 
 def run_test():
     """Run through the tests one by one"""
@@ -26,10 +56,9 @@ def run_test():
         print("SKIP: /proc/self/mem is not usable")
         print("----------------------------------")
         gdb_exit(77)
-    if "GITLAB_CI" in os.environ:
+    if not probe_proc_self_mem_access_prot_none():
         print("----------------------------------")
-        print("SKIP: fail on gitlab - " +
-              "https://gitlab.com/qemu-project/qemu/-/issues/3329")
+        print("SKIP: /proc/self/mem can't be used to access PROT_NONE page")
         print("----------------------------------")
         gdb_exit(77)
     gdb.Breakpoint("break_here")
-- 
2.43.0