scripts/gdb: add 'lx-kasan_mem_to_shadow' command

This command allows users to quickly translate memory address to the kasan
shadow memory address.

Example output:
(gdb) lx-kasan_mem_to_shadow 0xffff000019acc008
shadow addr: 0xffff600003359801

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Kuan-Ying Lee <[e-mail]>
Cc: Jan Kiszka <[e-mail]>
Cc: Kieran Bingham <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

scripts/gdb/linux/kasan.py

···
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright 2024 Canonical Ltd.
+#
+# Authors:
+#  Kuan-Ying Lee <[e-mail]>
+#
+
+import gdb
+from linux import constants, mm
+
+def help():
+    t = """Usage: lx-kasan_mem_to_shadow [Hex memory addr]
+    Example:
+        lx-kasan_mem_to_shadow 0xffff000008eca008\n"""
+    gdb.write("Unrecognized command\n")
+    raise gdb.GdbError(t)
+
+class KasanMemToShadow(gdb.Command):
+    """Translate memory address to kasan shadow address"""
+
+    p_ops = None
+
+    def __init__(self):
+        if constants.LX_CONFIG_KASAN_GENERIC or constants.LX_CONFIG_KASAN_SW_TAGS:
+            super(KasanMemToShadow, self).__init__("lx-kasan_mem_to_shadow", gdb.COMMAND_SUPPORT)
+
+    def invoke(self, args, from_tty):
+        if not constants.LX_CONFIG_KASAN_GENERIC or constants.LX_CONFIG_KASAN_SW_TAGS:
+            raise gdb.GdbError('CONFIG_KASAN_GENERIC or CONFIG_KASAN_SW_TAGS is not set')
+
+        argv = gdb.string_to_argv(args)
+        if len(argv) == 1:
+            if self.p_ops is None:
+                self.p_ops = mm.page_ops().ops
+            addr = int(argv[0], 16)
+            shadow_addr = self.kasan_mem_to_shadow(addr)
+            gdb.write('shadow addr: 0x%x\n' % shadow_addr)
+        else:
+            help()
+    def kasan_mem_to_shadow(self, addr):
+        return (addr >> self.p_ops.KASAN_SHADOW_SCALE_SHIFT) + self.p_ops.KASAN_SHADOW_OFFSET
+
+KasanMemToShadow()

scripts/gdb/vmlinux-gdb.py

···
     import linux.page_owner
     import linux.slab
     import linux.vmalloc
+    import linux.kasan