[PATCH qemu 1/2] Fix: TCG cross-page overflow for 32 bit guest

[PATCH qemu 1/2] Fix: TCG cross-page overflow for 32 bit guest

[~percival_foss]

From: foss@percivaleng.com <sean.stultz@percivaleng.com>

---
 accel/tcg/cputlb.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
index fb22048876..457b3f8ec7 100644
--- a/accel/tcg/cputlb.c
+++ b/accel/tcg/cputlb.c
@@ -1767,6 +1767,13 @@ static bool mmu_lookup(CPUState *cpu, vaddr addr, MemOpIdx oi,
         l->page[1].size = l->page[0].size - size0;
         l->page[0].size = size0;
 
+        /* check for wrapping address space on page crossing if target is 32 bit */
+        #if TARGET_LONG_BITS == 32
+        if (l->page[1].addr >= (1UL << TARGET_LONG_BITS)) {
+            l->page[1].addr %= (1UL << TARGET_LONG_BITS);
+        }
+        # endif
+
         /*
          * Lookup both pages, recognizing exceptions from either.  If the
          * second lookup potentially resized, refresh first CPUTLBEntryFull.
-- 
2.45.3

[PATCH qemu 2/2] Added TCG cross-page overflow test

[~percival_foss]

From: foss@percivaleng.com <sean.stultz@percivaleng.com>

---
 tests/functional/meson.build          |  1 +
 tests/functional/test_ppc_pegasos2.py | 69 +++++++++++++++++++++++++++
 2 files changed, 70 insertions(+)
 create mode 100755 tests/functional/test_ppc_pegasos2.py

diff --git a/tests/functional/meson.build b/tests/functional/meson.build
index 0f8be30fe2..6641b878c3 100644
--- a/tests/functional/meson.build
+++ b/tests/functional/meson.build
@@ -213,6 +213,7 @@ tests_ppc_system_thorough = [
   'ppc_bamboo',
   'ppc_mac',
   'ppc_mpc8544ds',
+  'ppc_pegasos2',
   'ppc_replay',
   'ppc_sam460ex',
   'ppc_tuxrun',
diff --git a/tests/functional/test_ppc_pegasos2.py b/tests/functional/test_ppc_pegasos2.py
new file mode 100755
index 0000000000..ef76745068
--- /dev/null
+++ b/tests/functional/test_ppc_pegasos2.py
@@ -0,0 +1,69 @@
+#!/usr/bin/env python3
+#
+# Test AmigaNG boards
+#
+# Copyright (c) 2023 BALATON Zoltan
+#
+# This work is licensed under the terms of the GNU GPL, version 2 or
+# later.  See the COPYING file in the top-level directory.
+
+import subprocess
+
+from qemu_test import QemuSystemTest, Asset
+from qemu_test import wait_for_console_pattern
+from zipfile import ZipFile
+
+class Pegasos2Machine(QemuSystemTest):
+
+    timeout = 90
+
+    ASSET_IMAGE = Asset(
+        ('https://web.archive.org/web/20071021223056if_/http://www.bplan-gmbh.de/up050404/up050404'),
+        '0b4ff042b293033e094b47ac7051824fc45f83adb340d455a17db1674b0150b0c60ffc624ac766f5369cd79f0447214d468baa182c1f18c5e04cd23a50f0b9a2')
+
+    def test_ppc_pegasos2(self):
+        self.require_accelerator("tcg")
+        self.set_machine('pegasos2')
+        file_path = self.ASSET_IMAGE.fetch()
+        bios_fh = open(self.workdir + "/pegasos2.rom", "wb")
+        subprocess.run(['tail', '-c','+85581', file_path], stdout=bios_fh)
+        bios_fh.close()
+        subprocess.run(['truncate', '-s', '524288', self.workdir + "/pegasos2.rom"], )
+
+        self.vm.set_console()
+        self.vm.add_args('-bios', self.workdir + '/pegasos2.rom')
+        self.vm.launch()
+        wait_for_console_pattern(self, 'SmartFirmware:')
+
+    def test_ppc_pegasos2_test_tcg_crosspage_overflow_bug(self):
+        self.require_accelerator("tcg")
+        self.set_machine('pegasos2')
+        file_path = self.ASSET_IMAGE.fetch()
+        bios_fh = open(self.workdir + "/pegasos2.rom", "wb")
+        subprocess.run(['tail', '-c','+85581', file_path], stdout=bios_fh)
+        bios_fh.close()
+        subprocess.run(['truncate', '-s', '524288', self.workdir + "/pegasos2.rom"], )
+
+        with open(self.workdir + "/pegasos2.rom", "rb") as bios_fh:
+            bios_data = bios_fh.read()
+        
+        # Patch the firmware image with the following instructions that will cause tcg to crash for 32-bit guests on 64-bit platforms:
+        #   li r3, 0
+        #   li r4, -1
+        #   lwz r5, 0x0(r4)
+        #   lwz r5, 0x0(r3)
+
+        bios_data_new = bios_data[:0x6c10] + b'\x38\x60\x00\x00' + b'\x38\x80\xff\xff' + b'\x80\xa4\x00\x00' + b'\x80\xa3\x00\x00' + bios_data[0x6c20:]
+        with open(self.workdir + "/pegasos2_new.rom", "wb") as bios_new_fh:
+            bios_new_fh.write(bios_data_new)
+
+        self.vm.set_console()
+        self.vm.add_args('-bios', self.workdir + '/pegasos2_new.rom')
+        self.vm.launch()
+        wait_for_console_pattern(self, 'Releasing IDE reset')
+
+        # set $pc = 0 and expect crash
+
+
+if __name__ == '__main__':
+    QemuSystemTest.main()
-- 
2.45.3

[PATCH qemu 0/2] Bugfix: TCG cross-page overflow for 32 bit guest

[~percival_foss]

The bug being resolved is that the current code in mmu_lookup() assumes
a valid 64-bit address space. If a guest has a 32-bit address space, a
page translation that crosses beyond the last page in the address space
will overflow out of the allocated guest virtual memory space in the
QEMU application and cause it to crash. In this case the first page will
be the last of the 32-bit address space (for example 0xFFFFF000 for 4K
page sizes) and the second page will overflow to a page beyond the
32-bit address space (0x100000000 in the very same example). An invalid
translation will be added to the cpu translation table from the second
page. Thought the translation will be for page address 0x100000000,
checks in other parts of the codebase actually enforce using only 32
bits, and will match this translation. Part of the stored translation is
the effective address, and another part is the addend to be used to
offset into the QEMU process's virtual memory space. The addend will
incorporate the 0x100000000 and offset into likely invalid virtual
address space.

The fix in the diff checks if the target is 32 bits and wraps the second
page address to the beginning of the memory space. Along with this we
have submitted a test to show this using Pegasos2

Singed off by: Percival Engineering <foss@percivalemg.com>

foss@percivaleng.com (2):
  Fix: TCG cross-page overflow for 32 bit guest
  Added TCG cross-page overflow test

 accel/tcg/cputlb.c                    |  7 +++
 tests/functional/meson.build          |  1 +
 tests/functional/test_ppc_pegasos2.py | 69 +++++++++++++++++++++++++++
 3 files changed, 77 insertions(+)
 create mode 100755 tests/functional/test_ppc_pegasos2.py

-- 
2.45.3