[3.14] gh-134876: Add fallback for when process_vm_readv fails with ENOSYS (GH-134878) (#135240)

gh-134876: Add fallback for when process_vm_readv fails with ENOSYS (GH-134878)
(cherry picked from commit ac9c3431cc5916a795c42b3e2b965233ceffe6f0)

Co-authored-by: Daniel Golding <goldingd89@gmail.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/Python/remote_debugging.c b/Python/remote_debugging.c
index dd55b78..7aee87e 100644
--- a/Python/remote_debugging.c
+++ b/Python/remote_debugging.c
@@ -24,6 +24,39 @@ read_memory(proc_handle_t *handle, uint64_t remote_address, size_t len, void* ds
     return _Py_RemoteDebug_ReadRemoteMemory(handle, remote_address, len, dst);
 }
 
+// Why is pwritev not guarded? Except on Android API level 23 (no longer
+// supported), HAVE_PROCESS_VM_READV is sufficient.
+#if defined(__linux__) && HAVE_PROCESS_VM_READV
+static int
+write_memory_fallback(proc_handle_t *handle, uintptr_t remote_address, size_t len, const void* src)
+{
+    if (handle->memfd == -1) {
+        if (open_proc_mem_fd(handle) < 0) {
+            return -1;
+        }
+    }
+
+    struct iovec local[1];
+    Py_ssize_t result = 0;
+    Py_ssize_t written = 0;
+
+    do {
+        local[0].iov_base = (char*)src + result;
+        local[0].iov_len = len - result;
+        off_t offset = remote_address + result;
+
+        written = pwritev(handle->memfd, local, 1, offset);
+        if (written < 0) {
+            PyErr_SetFromErrno(PyExc_OSError);
+            return -1;
+        }
+
+        result += written;
+    } while ((size_t)written != local[0].iov_len);
+    return 0;
+}
+#endif // __linux__
+
 static int
 write_memory(proc_handle_t *handle, uintptr_t remote_address, size_t len, const void* src)
 {
@@ -39,6 +72,9 @@ write_memory(proc_handle_t *handle, uintptr_t remote_address, size_t len, const
     } while (result < len);
     return 0;
 #elif defined(__linux__) && HAVE_PROCESS_VM_READV
+    if (handle->memfd != -1) {
+        return write_memory_fallback(handle, remote_address, len, src);
+    }
     struct iovec local[1];
     struct iovec remote[1];
     Py_ssize_t result = 0;
@@ -52,6 +88,9 @@ write_memory(proc_handle_t *handle, uintptr_t remote_address, size_t len, const
 
         written = process_vm_writev(handle->pid, local, 1, remote, 1, 0);
         if (written < 0) {
+            if (errno == ENOSYS) {
+                return write_memory_fallback(handle, remote_address, len, src);
+            }
             PyErr_SetFromErrno(PyExc_OSError);
             return -1;
         }