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

[Stefan Hajnoczi]

On Tue, 16 May 2023 at 06:20, 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>
> ---
>  hw/scsi/lsi53c895a.c               |  7 ++++++-
>  tests/qtest/fuzz-lsi53c895a-test.c | 33 ++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+), 1 deletion(-)
>
> diff --git a/hw/scsi/lsi53c895a.c b/hw/scsi/lsi53c895a.c
> index 048436352b..8b34199ab8 100644
> --- a/hw/scsi/lsi53c895a.c
> +++ b/hw/scsi/lsi53c895a.c
> @@ -1134,10 +1134,13 @@ 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) {
> +    if (++insn_processed > LSI_MAX_INSN || reentrancy_level > 8) {

Why 8 and not some other number?

>          /* 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.
> @@ -1596,6 +1599,8 @@ 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
>
>