feat: U4 ciphertext page dump tool

- utrw/debug.c: utrw_debug_dump_page(slot,page,offset) — kernel debug-privileged dump of 64B ciphertext + decrypted plaintext hex to serial (PCKC key derive, no capability path)
- selftest demo: dump at offset 128 shows plaintext 'deshab utsm sealed memory selftest' vs unrelated ciphertext; SELFTEST PASS (.build_tmp/qemu_serial_u4dump.log)

CODE/UTSM/utrw/debug.c

@@ -0,0 +1,88 @@
+#include <utsm/utrw.h>
+#include <utsm/segment.h>
+#include <utsm/pckc.h>
+#include <utsm/crypto.h>
+#include <utsm/log.h>
+
+void *memcpy(void *dst, const void *src, usize len);
+
+/* ===================================================================
+ *  U4: 密文页 dump 工具
+ *
+ *  "发疯也要可调试。"
+ *  对指定段页输出 密文 hex + 解密后明文 hex 对照——开发者可直接
+ *  在串口日志核对加密正确性（密文 != 明文、重读一致）。
+ *
+ *  内核调试特权路径：不经过 capability 校验（这正是工具的意义），
+ *  密钥经 PCKC 直接派生。仅调试用，不进任何热路径。
+ * =================================================================== */
+
+static void hexdump_line(const char *tag, u64 index, const u8 *data, u64 len) {
+    char buf[8 + 2 + 3 * 8 + 1];
+    /* "ssssssss: xx xx xx xx xx xx xx xx" */
+    static const char hexd[] = "0123456789abcdef";
+    for (int i = 0; i < 8; i++) {
+        u8 nib = (u8)((index >> ((7 - i) * 4)) & 0xF);
+        buf[i] = hexd[nib];
+    }
+    buf[8] = ':';
+    for (u64 b = 0; b < 8; b++) {
+        buf[9 + b * 3] = ' ';
+        u8 v = (b < len) ? data[b] : 0;
+        buf[10 + b * 3] = hexd[(v >> 4) & 0xF];
+        buf[11 + b * 3] = hexd[v & 0xF];
+    }
+    buf[9 + 8 * 3] = 0;
+    log_info(tag);
+    log_info(buf);
+}
+
+int utrw_debug_dump_page(u32 segment_slot, u64 page_index, u64 offset_in_page) {
+    utsm_segment_desc *desc = utsm_get_segment(segment_slot);
+    if (!desc || desc->state != UTSM_SEG_ACTIVE) {
+        return UTSM_ERR_INVALID;
+    }
+    u64 page_off = page_index * UTSM_PAGE_SIZE;
+    if (page_off + UTSM_PAGE_SIZE > desc->cipher_length ||
+        offset_in_page + 8 > UTSM_PAGE_SIZE) {
+        return UTSM_ERR_BOUNDS;
+    }
+
+    log_info("[UTRW] dump: segment");
+    log_hex64("[UTRW]   slot=", segment_slot);
+    log_hex64("[UTRW]   page=", page_index);
+    log_hex64("[UTRW]   offset=", offset_in_page);
+
+    const u8 *cipher = desc->cipher_base + page_off + offset_in_page;
+    const u64 SHOW = 64; /* 64B（1 cache line）足以核对 */
+
+    /* ---- 密文 hex ---- */
+    for (u64 off = 0; off < SHOW; off += 8) {
+        hexdump_line("[UTRW]   cipher=", page_off + offset_in_page + off, cipher + off, 8);
+    }
+
+    /* ---- 明文 hex（内核调试特权解密：PCKC 派生 + line 解密） ---- */
+    utsm_key_material key;
+    int st = utsm_pckc_get_or_derive(segment_slot, desc, &key);
+    if (st != UTSM_OK) {
+        log_warn("[UTRW] dump: key derive failed");
+        return st;
+    }
+    u64 dump_line = (page_off + offset_in_page) / UTSM_CACHE_LINE_SIZE;
+    u8 plain[UTSM_CACHE_LINE_SIZE];
+    {
+        u64 tweak = utsm_make_tweak(desc->tweak_seed, dump_line, desc->key_epoch);
+        utsm_crypt_line(&key, tweak,
+                        desc->cipher_base + dump_line * UTSM_CACHE_LINE_SIZE, plain);
+    }
+    u64 in_line = (page_off + offset_in_page) % UTSM_CACHE_LINE_SIZE;
+    for (u64 off = 0; off < SHOW; off += 8) {
+        u64 src = in_line + off;
+        if (src >= UTSM_CACHE_LINE_SIZE) break;
+        hexdump_line("[UTRW]   plain= ", page_off + offset_in_page + off,
+                     plain + src, 8);
+    }
+
+    log_info("[UTRW] dump done");
+    return UTSM_OK;
+}

CODE/UTSM/utrw/debug.d

@@ -0,0 +1,15 @@
+utrw/debug.o: utrw\debug.c include\utsm\utrw.h include\utsm\types.h \
+  include\utsm\status.h include\utsm\capability.h include\utsm\segment.h \
+  include\utsm\uuid.h include\utsm\dirty.h include\utsm\pckc.h \
+  include\utsm\config.h include\utsm\crypto.h include\utsm\log.h
+include\utsm\utrw.h:
+include\utsm\types.h:
+include\utsm\status.h:
+include\utsm\capability.h:
+include\utsm\segment.h:
+include\utsm\uuid.h:
+include\utsm\dirty.h:
+include\utsm\pckc.h:
+include\utsm\config.h:
+include\utsm\crypto.h:
+include\utsm\log.h: