[PATCH v2] hw/scsi/lsi53c895a: Fix reentrancy issues in the LSI controller (CVE-2023-0330)

[Thomas Huth <thuth@redhat.com>]

We cannot use the generic reentrancy guard in the LSI code, so
we have to manually prevent endless reentrancy here. The problematic
lsi_execute_script() function has already a way to detect whether
too many instructions have been executed - we just have to slightly
change the logic here that it also takes into account if the function
has been called too often in a reentrant way.

The code in fuzz-lsi53c895a-test.c has been taken from an earlier
patch by Mauro Matteo Cascella.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1563
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 v2: Add a comment about the reentrancy problem to the source code

 hw/scsi/lsi53c895a.c               | 23 +++++++++++++++------
 tests/qtest/fuzz-lsi53c895a-test.c | 33 ++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/hw/scsi/lsi53c895a.c b/hw/scsi/lsi53c895a.c
index 048436352b..f7d45b0b20 100644
--- a/hw/scsi/lsi53c895a.c
+++ b/hw/scsi/lsi53c895a.c
@@ -1134,15 +1134,24 @@ static void lsi_execute_script(LSIState *s)
     uint32_t addr, addr_high;
     int opcode;
     int insn_processed = 0;
+    static int reentrancy_level;
+
+    reentrancy_level++;
 
     s->istat1 |= LSI_ISTAT1_SRUN;
 again:
-    if (++insn_processed > LSI_MAX_INSN) {
-        /* Some windows drivers make the device spin waiting for a memory
-           location to change.  If we have been executed a lot of code then
-           assume this is the case and force an unexpected device disconnect.
-           This is apparently sufficient to beat the drivers into submission.
-         */
+    /*
+     * Some windows drivers make the device spin waiting for a memory location
+     * to change. If we have executed more than LSI_MAX_INSN instructions then
+     * assume this is the case and force an unexpected device disconnect. This
+     * is apparently sufficient to beat the drivers into submission.
+     *
+     * Another issue (CVE-2023-0330) can occur if the script is programmed to
+     * trigger itself again and again. Avoid this problem by stopping after
+     * being called multiple times in a reentrant way (8 is an arbitrary value
+     * which should be enough for all valid use cases).
+     */
+    if (++insn_processed > LSI_MAX_INSN || reentrancy_level > 8) {
         if (!(s->sien0 & LSI_SIST0_UDC)) {
             qemu_log_mask(LOG_GUEST_ERROR,
                           "lsi_scsi: inf. loop with UDC masked");
@@ -1596,6 +1605,8 @@ again:
         }
     }
     trace_lsi_execute_script_stop();
+
+    reentrancy_level--;
 }
 
 static uint8_t lsi_reg_readb(LSIState *s, int offset)
diff --git a/tests/qtest/fuzz-lsi53c895a-test.c b/tests/qtest/fuzz-lsi53c895a-test.c
index 2012bd54b7..1b55928b9f 100644
--- a/tests/qtest/fuzz-lsi53c895a-test.c
+++ b/tests/qtest/fuzz-lsi53c895a-test.c
@@ -8,6 +8,36 @@
 #include "qemu/osdep.h"
 #include "libqtest.h"
 
+/*
+ * This used to trigger a DMA reentrancy issue
+ * leading to memory corruption bugs like stack
+ * overflow or use-after-free
+ * https://gitlab.com/qemu-project/qemu/-/issues/1563
+ */
+static void test_lsi_dma_reentrancy(void)
+{
+    QTestState *s;
+
+    s = qtest_init("-M q35 -m 512M -nodefaults "
+                   "-blockdev driver=null-co,node-name=null0 "
+                   "-device lsi53c810 -device scsi-cd,drive=null0");
+
+    qtest_outl(s, 0xcf8, 0x80000804); /* PCI Command Register */
+    qtest_outw(s, 0xcfc, 0x7);        /* Enables accesses */
+    qtest_outl(s, 0xcf8, 0x80000814); /* Memory Bar 1 */
+    qtest_outl(s, 0xcfc, 0xff100000); /* Set MMIO Address*/
+    qtest_outl(s, 0xcf8, 0x80000818); /* Memory Bar 2 */
+    qtest_outl(s, 0xcfc, 0xff000000); /* Set RAM Address*/
+    qtest_writel(s, 0xff000000, 0xc0000024);
+    qtest_writel(s, 0xff000114, 0x00000080);
+    qtest_writel(s, 0xff00012c, 0xff000000);
+    qtest_writel(s, 0xff000004, 0xff000114);
+    qtest_writel(s, 0xff000008, 0xff100014);
+    qtest_writel(s, 0xff10002f, 0x000000ff);
+
+    qtest_quit(s);
+}
+
 /*
  * This used to trigger a UAF in lsi_do_msgout()
  * https://gitlab.com/qemu-project/qemu/-/issues/972
@@ -124,5 +154,8 @@ int main(int argc, char **argv)
     qtest_add_func("fuzz/lsi53c895a/lsi_do_msgout_cancel_req",
                    test_lsi_do_msgout_cancel_req);
 
+    qtest_add_func("fuzz/lsi53c895a/lsi_dma_reentrancy",
+                   test_lsi_dma_reentrancy);
+
     return g_test_run();
 }
-- 
2.31.1