On 8/26/2026 5:41 AM, Alex Bennée wrote:
> Pierrick Bouvier <[email protected]> writes:
>
>> 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
>
> It might be worth pointing to it here:
>
> modified tests/tcg/multiarch/gdbstub/prot-none.py
> @@ -34,6 +34,7 @@ def probe_proc_self_mem_access_prot_none():
> fd = os.open("/proc/self/mem", os.O_RDWR)
> try:
> # read it through /proc/self/mem
> + # this is the fallback in cpu_memory_rw_debug
Added.
> data = os.pread(fd, size, addr)
> except Exception as e:
> print("/proc/self/mem pread error: " + str(e))
>
> I think the comment in cpu_memory_rw_debug is wrong through, pread isn't
> using the ptrace interface.
>
> Otherwise:
>
> Reviewed-by: Alex Bennée <[email protected]>
>
