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
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]>
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
