Re: [PATCH 1/4] esp: don't underflow cmdfifo if no message out/command data is present

[Alexander Bulekov]

On 210316 2330, Mark Cave-Ayland wrote:
> If a guest sends a TI (Transfer Information) command without previously 
> sending
> any message out/command phase data then cmdfifo will underflow triggering an
> assert reading the IDENTIFY byte.
> 
> Buglink: https://bugs.launchpad.net/qemu/+bug/1919035
> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>

Hi Mark,
The original reproducer no longer asserts, but I ran through the fuzz
corpus, and there is another one, that still seems to trigger the same
bug:

cat << EOF | ./qemu-system-i386 -display none -machine accel=qtest, \
-m 512M -device am53c974,id=scsi -device scsi-hd,drive=disk0 -drive \
id=disk0,if=none,file=null-co://,format=raw -nodefaults -qtest stdio
outl 0xcf8 0x80001010
outl 0xcfc 0xc000
outl 0xcf8 0x80001004
outw 0xcfc 0x01
outl 0xc008 0x0a
outl 0xc009 0x41000000
outl 0xc009 0x41000000
outl 0xc00b 0x1000
EOF

C Code testcase below.
Thanks
-Alex

/*
 * Autogenerated Fuzzer Test Case
 *
 * Copyright (c) 2021 <name of author>
 *
 * This work is licensed under the terms of the GNU GPL, version 2 or
 * later. See the COPYING file in the top-level directory.
 */

#include "qemu/osdep.h"

#include "libqos/libqtest.h"

/*
 * cat << EOF | ./qemu-system-i386 -display none -machine accel=qtest, \
 * -m 512M -device am53c974,id=scsi -device scsi-hd,drive=disk0 -drive \
 * id=disk0,if=none,file=null-co://,format=raw -nodefaults -qtest stdio
 * outl 0xcf8 0x80001010
 * outl 0xcfc 0xc000
 * outl 0xcf8 0x80001004
 * outw 0xcfc 0x01
 * outl 0xc008 0x0a
 * outl 0xc009 0x41000000
 * outl 0xc009 0x41000000
 * outl 0xc00b 0x1000
 * EOF
 */
static void test_fuzz(void)
{
    QTestState *s = qtest_init(
        "-display none , -m 512M -device am53c974,id=scsi -device "
        "scsi-hd,drive=disk0 -drive "
        "id=disk0,if=none,file=null-co://,format=raw -nodefaults ");
    qtest_outl(s, 0xcf8, 0x80001010);
    qtest_outl(s, 0xcfc, 0xc000);
    qtest_outl(s, 0xcf8, 0x80001004);
    qtest_outw(s, 0xcfc, 0x01);
    qtest_outl(s, 0xc008, 0x0a);
    qtest_outl(s, 0xc009, 0x41000000);
    qtest_outl(s, 0xc009, 0x41000000);
    qtest_outl(s, 0xc00b, 0x1000);
    qtest_quit(s);
}
int main(int argc, char **argv)
{
    const char *arch = qtest_get_arch();

    g_test_init(&argc, &argv, NULL);

    if (strcmp(arch, "i386") == 0) {
        qtest_add_func("fuzz/test_fuzz", test_fuzz);
    }

    return g_test_run();
}