[PATCH v2] scripts/gdb: add mm introspection utils

[Dmitrii Bundin <dmitrii.bundin.a@gmail.com>]

This command provides a way to traverse the entire page hierarchy by a
given virtual address on x86. In addition to qemu's commands info
tlb/info mem it provides the complete information about the paging
structure for an arbitrary virtual address. It supports 4KB/2MB/1GB and
5 level paging.

Here is an example output for 2MB success translation:

(gdb) translate-vm address
CR3:
    CR3 BINARY DATA: 0x10c1d2002
    NEXT ENTRY PHYSICALL ADDRESS: 0x10c1d2000
    ---
    PAGE LEVEL WRITE THROUGH(bit 3): False
    PAGE LEVEL CACHE DISABLED(bit 4): False
LEVEL 4:
    ENTRY ADDRESS: 0xffff88810c1d27f0
    PAGE ENTRY BINARY DATA: 0x8000000105dca067
    NEXT ENTRY PHYSICALL ADDRESS: 0x105dca000
    ---
    ENTRY PRESENT(bit 0):      True
    READ/WRITE ACCESS ALLOWED(bit 1): True
    USER ACCESS ALLOWED(bit 2): True
    PAGE LEVEL WRITE THROUGH(bit 3): False
    PAGE LEVEL CACHE DISABLED(bit 4): False
    ENTRY HAS BEEN ACCESSED(bit 5): True
    PAGE SIZE(bit 7): False
    RESTART TO ORDINARY(bit 11): False
    EXECUTE DISABLE(bit 63): True
LEVEL 3:
    ENTRY ADDRESS: 0xffff888105dca9d0
    PAGE ENTRY BINARY DATA: 0x105c87067
    NEXT ENTRY PHYSICALL ADDRESS: 0x105c87000
    ---
    ENTRY PRESENT(bit 0):      True
    READ/WRITE ACCESS ALLOWED(bit 1): True
    USER ACCESS ALLOWED(bit 2): True
    PAGE LEVEL WRITE THROUGH(bit 3): False
    PAGE LEVEL CACHE DISABLED(bit 4): False
    ENTRY HAS BEEN ACCESSED(bit 5): True
    PAGE SIZE(bit 7): False
    RESTART TO ORDINARY(bit 11): False
    EXECUTE DISABLE(bit 63): False
LEVEL 2:
    ENTRY ADDRESS: 0xffff888105c87698
    PAGE ENTRY BINARY DATA: 0x80000001622008e7
    PAGE SIZE: 2MB
    PAGE PHYSICALL ADDRESS: 0x162200000
    ---
    ENTRY PRESENT(bit 0):      True
    READ/WRITE ACCESS ALLOWED(bit 1): True
    USER ACCESS ALLOWED(bit 2): True
    PAGE LEVEL WRITE THROUGH(bit 3): False
    PAGE LEVEL CACHE DISABLED(bit 4): False
    ENTRY HAS BEEN ACCESSED(bit 5): True
    PAGE DIRTY(bit 6): True
    PAGE SIZE(bit 7): True
    GLOBAL TRANSLATION(bit 8): False
    RESTART TO ORDINARY(bit 11): True
    PAT(bit 12): False
    PROTECTION KEY(bits (62, 59)): 0
    EXECUTE DISABLE(bit 63): True

Signed-off-by: Dmitrii Bundin <dmitrii.bundin.a@gmail.com>
---

Changes in v2: https://lore.kernel.org/all/20221230163512.23736-1-dmitrii.bundin.a@gmail.com/
    - Fix commit message to mention x86 explicitly
    - Assign page_offset_base to a constant in case
      CONFIG_DYNAMIC_MEMORY_LAYOUT is disabled

 scripts/gdb/linux/mm.py    | 222 +++++++++++++++++++++++++++++++++++++
 scripts/gdb/vmlinux-gdb.py |   1 +
 2 files changed, 223 insertions(+)
 create mode 100644 scripts/gdb/linux/mm.py

diff --git a/scripts/gdb/linux/mm.py b/scripts/gdb/linux/mm.py
new file mode 100644
index 000000000000..1b1d59872b25
--- /dev/null
+++ b/scripts/gdb/linux/mm.py
@@ -0,0 +1,222 @@
+#
+# gdb helper commands and functions for Linux kernel debugging
+#
+#  routines to introspect page table
+#
+# Authors:
+#  Dmitrii Bundin <dmitrii.bundin.a@gmail.com>
+#
+# This work is licensed under the terms of the GNU GPL version 2.
+#
+
+import gdb
+
+from linux import utils
+
+PHYSICAL_ADDRESS_MASK = gdb.parse_and_eval('0xfffffffffffff')
+
+
+def page_mask(level=1):
+    # 4KB
+    if level == 1:
+        return gdb.parse_and_eval('(u64) ~0xfff')
+    # 2MB
+    elif level == 2:
+        return gdb.parse_and_eval('(u64) ~0x1fffff')
+    # 1GB
+    elif level == 3:
+        return gdb.parse_and_eval('(u64) ~0x3fffffff')
+    else:
+        raise Exception(f'Unknown page level: {level}')
+
+
+#page_offset_base in case CONFIG_DYNAMIC_MEMORY_LAYOUT is disabled
+POB_NO_DYNAMIC_MEM_LAYOUT = '0xffff888000000000'
+def _page_offset_base():
+    pob_symbol = gdb.lookup_global_symbol('page_offset_base')
+    pob = pob_symbol.name if pob_symbol else POB_NO_DYNAMIC_MEM_LAYOUT
+    return gdb.parse_and_eval(pob)
+
+
+def is_bit_defined_tupled(data, offset):
+    return offset, bool(data >> offset & 1)
+
+def content_tupled(data, bit_start, bit_end):
+    return (bit_end, bit_start), data >> bit_start & ((1 << (1 + bit_end - bit_start)) - 1)
+
+def entry_va(level, phys_addr, translating_va):
+        def start_bit(level):
+            if level == 5:
+                return 48
+            elif level == 4:
+                return 39
+            elif level == 3:
+                return 30
+            elif level == 2:
+                return 21
+            elif level == 1:
+                return 12
+            else:
+                raise Exception(f'Unknown level {level}')
+
+        entry_offset =  ((translating_va >> start_bit(level)) & 511) * 8
+        entry_va = _page_offset_base() + phys_addr + entry_offset
+        return entry_va
+
+class Cr3():
+    def __init__(self, cr3, page_levels):
+        self.cr3 = cr3
+        self.page_levels = page_levels
+        self.page_level_write_through = is_bit_defined_tupled(cr3, 3)
+        self.page_level_cache_disabled = is_bit_defined_tupled(cr3, 4)
+        self.next_entry_physical_address = cr3 & PHYSICAL_ADDRESS_MASK & page_mask()
+
+    def next_entry(self, va):
+        next_level = self.page_levels
+        return PageHierarchyEntry(entry_va(next_level, self.next_entry_physical_address, va), next_level)
+
+    def mk_string(self):
+            return f"""\
+CR3:
+    CR3 BINARY DATA: {hex(self.cr3)}
+    NEXT ENTRY PHYSICALL ADDRESS: {hex(self.next_entry_physical_address)}
+    ---
+    PAGE LEVEL WRITE THROUGH(bit {self.page_level_write_through[0]}): {self.page_level_write_through[1]}
+    PAGE LEVEL CACHE DISABLED(bit {self.page_level_cache_disabled[0]}): {self.page_level_cache_disabled[1]}
+"""
+
+
+class PageHierarchyEntry():
+    def __init__(self, address, level):
+        data = int.from_bytes(
+            memoryview(gdb.selected_inferior().read_memory(address, 8)),
+            "little"
+        )
+        if level == 1:
+            self.is_page = True
+            self.entry_present = is_bit_defined_tupled(data, 0)
+            self.read_write = is_bit_defined_tupled(data, 1)
+            self.user_access_allowed = is_bit_defined_tupled(data, 2)
+            self.page_level_write_through = is_bit_defined_tupled(data, 3)
+            self.page_level_cache_disabled = is_bit_defined_tupled(data, 4)
+            self.entry_was_accessed = is_bit_defined_tupled(data, 5)
+            self.dirty = is_bit_defined_tupled(data, 6)
+            self.pat = is_bit_defined_tupled(data, 7)
+            self.global_translation = is_bit_defined_tupled(data, 8)
+            self.page_physical_address = data & PHYSICAL_ADDRESS_MASK & page_mask(level)
+            self.next_entry_physical_address = None
+            self.hlat_restart_with_ordinary = is_bit_defined_tupled(data, 11)
+            self.protection_key = content_tupled(data, 59, 62)
+            self.executed_disable = is_bit_defined_tupled(data, 63)
+        else:
+            page_size = is_bit_defined_tupled(data, 7)
+            page_size_bit = page_size[1]
+            self.is_page = page_size_bit
+            self.entry_present = is_bit_defined_tupled(data, 0)
+            self.read_write = is_bit_defined_tupled(data, 1)
+            self.user_access_allowed = is_bit_defined_tupled(data, 2)
+            self.page_level_write_through = is_bit_defined_tupled(data, 3)
+            self.page_level_cache_disabled = is_bit_defined_tupled(data, 4)
+            self.entry_was_accessed = is_bit_defined_tupled(data, 5)
+            self.page_size = page_size
+            self.dirty = is_bit_defined_tupled(
+                data, 6) if page_size_bit else None
+            self.global_translation = is_bit_defined_tupled(
+                data, 8) if page_size_bit else None
+            self.pat = is_bit_defined_tupled(
+                data, 12) if page_size_bit else None
+            self.page_physical_address = data & PHYSICAL_ADDRESS_MASK & page_mask(level) if page_size_bit else None
+            self.next_entry_physical_address = None if page_size_bit else data & PHYSICAL_ADDRESS_MASK & page_mask()
+            self.hlat_restart_with_ordinary = is_bit_defined_tupled(data, 11)
+            self.protection_key = content_tupled(data, 59, 62) if page_size_bit else None
+            self.executed_disable = is_bit_defined_tupled(data, 63)
+        self.address = address
+        self.page_entry_binary_data = data
+        self.page_hierarchy_level = level
+
+    def next_entry(self, va):
+        if self.is_page or not self.entry_present[1]:
+            return None
+
+        next_level = self.page_hierarchy_level - 1
+        return PageHierarchyEntry(entry_va(next_level, self.next_entry_physical_address, va), next_level)
+
+
+    def mk_string(self):
+        if not self.entry_present[1]:
+            return f"""\
+LEVEL {self.page_hierarchy_level}:
+    ENTRY ADDRESS: {hex(self.address)}
+    PAGE ENTRY BINARY DATA: {hex(self.page_entry_binary_data)}
+    ---
+    PAGE ENTRY IS NOT PRESENT!
+"""
+        elif self.is_page:
+            return f"""\
+LEVEL {self.page_hierarchy_level}:
+    ENTRY ADDRESS: {hex(self.address)}
+    PAGE ENTRY BINARY DATA: {hex(self.page_entry_binary_data)}
+    PAGE SIZE: {'1GB' if self.page_hierarchy_level == 3 else '2MB' if self.page_hierarchy_level == 2 else '4KB' if self.page_hierarchy_level == 1 else 'Unknown page size for level:' + self.page_hierarchy_level}
+    PAGE PHYSICALL ADDRESS: {hex(self.page_physical_address)}
+    ---
+    ENTRY PRESENT(bit {self.entry_present[0]}):      {self.entry_present[1]}
+    READ/WRITE ACCESS ALLOWED(bit {self.read_write[0]}): {self.read_write[1]}
+    USER ACCESS ALLOWED(bit {self.user_access_allowed[0]}): {self.user_access_allowed[1]}
+    PAGE LEVEL WRITE THROUGH(bit {self.page_level_write_through[0]}): {self.page_level_write_through[1]}
+    PAGE LEVEL CACHE DISABLED(bit {self.page_level_cache_disabled[0]}): {self.page_level_cache_disabled[1]}
+    ENTRY HAS BEEN ACCESSED(bit {self.entry_was_accessed[0]}): {self.entry_was_accessed[1]}
+    PAGE DIRTY(bit {self.dirty[0]}): {self.dirty[1]}
+    """ + \
+    ("" if self.page_hierarchy_level == 1 else f"""PAGE SIZE(bit {self.page_size[0]}): {self.page_size[1]}
+    """) + \
+    f"""GLOBAL TRANSLATION(bit {self.global_translation[0]}): {self.global_translation[1]}
+    RESTART TO ORDINARY(bit {self.hlat_restart_with_ordinary[0]}): {self.hlat_restart_with_ordinary[1]}
+    PAT(bit {self.pat[0]}): {self.pat[1]}
+    PROTECTION KEY(bits {self.protection_key[0]}): {self.protection_key[1]}
+    EXECUTE DISABLE(bit {self.executed_disable[0]}): {self.executed_disable[1]}
+"""
+        else:
+            return f"""\
+LEVEL {self.page_hierarchy_level}:
+    ENTRY ADDRESS: {hex(self.address)}
+    PAGE ENTRY BINARY DATA: {hex(self.page_entry_binary_data)}
+    NEXT ENTRY PHYSICALL ADDRESS: {hex(self.next_entry_physical_address)}
+    ---
+    ENTRY PRESENT(bit {self.entry_present[0]}):      {self.entry_present[1]}
+    READ/WRITE ACCESS ALLOWED(bit {self.read_write[0]}): {self.read_write[1]}
+    USER ACCESS ALLOWED(bit {self.user_access_allowed[0]}): {self.user_access_allowed[1]}
+    PAGE LEVEL WRITE THROUGH(bit {self.page_level_write_through[0]}): {self.page_level_write_through[1]}
+    PAGE LEVEL CACHE DISABLED(bit {self.page_level_cache_disabled[0]}): {self.page_level_cache_disabled[1]}
+    ENTRY HAS BEEN ACCESSED(bit {self.entry_was_accessed[0]}): {self.entry_was_accessed[1]}
+    PAGE SIZE(bit {self.page_size[0]}): {self.page_size[1]}
+    RESTART TO ORDINARY(bit {self.hlat_restart_with_ordinary[0]}): {self.hlat_restart_with_ordinary[1]}
+    EXECUTE DISABLE(bit {self.executed_disable[0]}): {self.executed_disable[1]}
+"""
+
+
+class TranslateVM(gdb.Command):
+    """Prints the entire paging structure used to translate a given virtual address.
+
+Having an address space of the currently executed process translates the virtual address
+and prints detailed information of all paging structure levels used for the transaltion."""
+
+    def __init__(self):
+        super(TranslateVM, self).__init__('translate-vm', gdb.COMMAND_USER)
+
+    def invoke(self, arg, from_tty):
+        if utils.is_target_arch("x86"):
+            vm_address = gdb.parse_and_eval(f'{arg}')
+            cr3_data = gdb.parse_and_eval('$cr3')
+            cr4 = gdb.parse_and_eval('$cr4')
+            page_levels = 5 if cr4 & (1 << 12) else 4
+            page_entry = Cr3(cr3_data, page_levels)
+            while page_entry:
+                gdb.write(page_entry.mk_string())
+                page_entry = page_entry.next_entry(vm_address)
+        else:
+            gdb.GdbError("Virtual address translation is not"
+                         "supported for this arch")
+
+
+
+TranslateVM()
diff --git a/scripts/gdb/vmlinux-gdb.py b/scripts/gdb/vmlinux-gdb.py
index 4136dc2c59df..27bd7339bccc 100644
--- a/scripts/gdb/vmlinux-gdb.py
+++ b/scripts/gdb/vmlinux-gdb.py
@@ -37,3 +37,4 @@ else:
     import linux.clk
     import linux.genpd
     import linux.device
+    import linux.mm
-- 
2.17.1