From: P J P <ppandit@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Fam Zheng" <fam@euphon.net>,
"Marcelo Tosatti" <mtosatti@redhat.com>,
"Mark Cave-Ayland" <mark.cave-ayland@ilande.co.uk>,
"QEMU Developers" <qemu-devel@nongnu.org>,
"Bugs SysSec" <bugs-syssec@rub.de>,
"Philippe Mathieu-Daudé" <philmd@redhat.com>,
"Stefano Garzarella" <sgarzare@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v3 1/2] scsi: lsi: exit infinite loop while executing script (CVE-2019-12068)
Date: Wed, 14 Aug 2019 15:55:41 +0530 (IST) [thread overview]
Message-ID: <nycvar.YSQ.7.76.1908141450520.30613@xnncv> (raw)
In-Reply-To: <3a48e557-985d-7274-81d9-fe963f74e59a@redhat.com>
+-- On Tue, 13 Aug 2019, Paolo Bonzini wrote --+
| After the first instruction is processed, "again" is only reached if
| s->waiting == LSI_NOWAIT. Therefore, we could move the Windows hack to the
| beginning and remove the s->waiting condition. The only change would be
| that it would also be triggered by all zero instructions, like this:
|
| diff --git a/hw/scsi/lsi53c895a.c b/hw/scsi/lsi53c895a.c
| index 10468c1..9d714af 100644
| --- a/hw/scsi/lsi53c895a.c
| +++ b/hw/scsi/lsi53c895a.c
| @@ -185,6 +185,9 @@ static const char *names[] = {
| /* Flag set if this is a tagged command. */
| #define LSI_TAG_VALID (1 << 16)
|
| +/* Maximum instructions to process. */
| +#define LSI_MAX_INSN 10000
| +
| typedef struct lsi_request {
| SCSIRequest *req;
| uint32_t tag;
| @@ -1132,7 +1135,19 @@ static void lsi_execute_script(LSIState *s)
|
| s->istat1 |= LSI_ISTAT1_SRUN;
| again:
| - insn_processed++;
| + 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.
| + */
| + if (!(s->sien0 & LSI_SIST0_UDC)) {
| + qemu_log_mask(LOG_GUEST_ERROR,
| + "lsi_scsi: inf. loop with UDC masked");
| + }
| + lsi_script_scsi_interrupt(s, LSI_SIST0_UDC, 0);
| + lsi_disconnect(s);
...
|
| Does it make sense?
Yes, this'd also work, but need to return after lsi_disconnect(s), otherwise
loop would continue.
Should I send a revised patch? (with above change)
Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
47AF CE69 3A90 54AA 9045 1053 DD13 3D32 FE5B 041F
next prev parent reply other threads:[~2019-08-14 10:27 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-09 6:38 [Qemu-devel] [PATCH v3 0/2] scsi: lsi: break infinite loop after 10k instructions P J P
2019-08-09 6:38 ` [Qemu-devel] [PATCH v3 1/2] scsi: lsi: exit infinite loop while executing script (CVE-2019-12068) P J P
2019-08-13 10:05 ` P J P
2019-08-13 10:31 ` Philippe Mathieu-Daudé
2019-08-13 14:33 ` Paolo Bonzini
2019-08-14 10:25 ` P J P [this message]
2019-08-14 10:38 ` Paolo Bonzini
2019-08-14 12:08 ` P J P
2019-08-09 6:38 ` [Qemu-devel] [PATCH v3 2/2] scsi: lsi: use macro LSI_MAX_INSN instead of a magic number P J P
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