hw/scsi/lsi53c895a.c | 23 +++++++++++++++------ tests/qtest/fuzz-lsi53c895a-test.c | 33 ++++++++++++++++++++++++++++++ 2 files changed, 50 insertions(+), 6 deletions(-)
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();
}
--
2.31.1On 230522 1110, Thomas Huth wrote: > 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> Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
On Mon, 22 May 2023 at 05:11, Thomas Huth <thuth@redhat.com> wrote: > > 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(-) Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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