Hi Michael,
On 4/14/25 9:32 AM, Michael S. Tsirkin wrote:
> On Wed, Apr 02, 2025 at 11:29:54PM -0700, Dongli Zhang wrote:
>> Since long time ago, the only user of vq->log is vhost-net. The concern is
>> to add support for more devices (i.e. vhost-scsi or vsock) may reveals
>> unknown issue in the vhost API. Add a WARNING.
>>
>> Suggested-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
>> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
>
>
> Userspace can trigger this I think, this is a problem since
> people run with reboot on warn.
I think it will be a severe kernel bug (page fault) if userspace can trigger this.
If (*log_num >= vq->dev->iov_limit), the next line will lead to an out-of-bound
memory access:
log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
I could not propose a case to trigger the WARNING from userspace. Would you mind
helping explain if that can happen?
> Pls grammar issues in comments... I don't think so.
I did an analysis of code and so far I could not identify any case to trigger
(*log_num >= vq->dev->iov_limit).
The objective of the patch is to add a WARNING to double confirm the case won't
happen.
Regarding "I don't think so", would you mean we don't need this patch/WARNING
because the code is robust enough?
Thank you very much!
Dongli Zhang
>
>> ---
>> drivers/vhost/vhost.c | 18 ++++++++++++++++++
>> 1 file changed, 18 insertions(+)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 494b3da5423a..b7d51d569646 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -2559,6 +2559,15 @@ static int get_indirect(struct vhost_virtqueue *vq,
>> if (access == VHOST_ACCESS_WO) {
>> *in_num += ret;
>> if (unlikely(log && ret)) {
>> + /*
>> + * Since long time ago, the only user of
>> + * vq->log is vhost-net. The concern is to
>> + * add support for more devices (i.e.
>> + * vhost-scsi or vsock) may reveals unknown
>> + * issue in the vhost API. Add a WARNING.
>> + */
>> + WARN_ON_ONCE(*log_num >= vq->dev->iov_limit);
>> +
>> log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
>> log[*log_num].len = vhost32_to_cpu(vq, desc.len);
>> ++*log_num;
>> @@ -2679,6 +2688,15 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
>> * increment that count. */
>> *in_num += ret;
>> if (unlikely(log && ret)) {
>> + /*
>> + * Since long time ago, the only user of
>> + * vq->log is vhost-net. The concern is to
>> + * add support for more devices (i.e.
>> + * vhost-scsi or vsock) may reveals unknown
>> + * issue in the vhost API. Add a WARNING.
>> + */
>> + WARN_ON_ONCE(*log_num >= vq->dev->iov_limit);
>> +
>> log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
>> log[*log_num].len = vhost32_to_cpu(vq, desc.len);
>> ++*log_num;
>> --
>> 2.39.3
>
