* RE: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
@ 2017-10-30 11:07 ` Hatayama, Daisuke
0 siblings, 0 replies; 9+ messages in thread
From: Hatayama, Daisuke @ 2017-10-30 11:07 UTC (permalink / raw)
To: 'marcandre.lureau@redhat.com'
Cc: 'somlo@cmu.edu', 'mst@redhat.com',
linux-kernel, 'qemu-devel@nongnu.org'
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>
> Since qemu 2.9, DMA write operations are allowed. However, usage of this
> interface from kernel or user-space is strongly discouraged by the
> maintainers. This patch is meant for experimentations for now.
>
Could you (or maintainers?) tell me how experimental the DMA write
operations from kernel are?
>From some technical reason?
Or simply there has not been enough test yet so far?
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
> drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index 54b569da3257..e2f2ad1c9c0c 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
> return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> }
>
> +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject *kobj,
> + struct bin_attribute *bin_attr,
> + char *buf, loff_t pos, size_t count)
> +{
> + struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> +
> + if (!fw_cfg_dma_enabled())
> + return -ENOTSUPP;
> +
> + if (pos > entry->f.size)
> + return -EINVAL;
> +
> + if (count > entry->f.size - pos)
> + count = entry->f.size - pos;
> +
> + return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> +}
> +
> static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> - .attr = { .name = "raw", .mode = S_IRUSR },
> + .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
> .read = fw_cfg_sysfs_read_raw,
> + .write = fw_cfg_sysfs_write_raw,
> };
>
> /*
> --
> 2.14.1.146.gd35faa819
Thanks.
HATAYAMA, Daisuke
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
@ 2017-10-30 11:07 ` Hatayama, Daisuke
0 siblings, 0 replies; 9+ messages in thread
From: Hatayama, Daisuke @ 2017-10-30 11:07 UTC (permalink / raw)
To: 'marcandre.lureau@redhat.com'
Cc: 'somlo@cmu.edu', 'mst@redhat.com',
linux-kernel, 'qemu-devel@nongnu.org'
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>
> Since qemu 2.9, DMA write operations are allowed. However, usage of this
> interface from kernel or user-space is strongly discouraged by the
> maintainers. This patch is meant for experimentations for now.
>
Could you (or maintainers?) tell me how experimental the DMA write
operations from kernel are?
From some technical reason?
Or simply there has not been enough test yet so far?
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
> drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> index 54b569da3257..e2f2ad1c9c0c 100644
> --- a/drivers/firmware/qemu_fw_cfg.c
> +++ b/drivers/firmware/qemu_fw_cfg.c
> @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
> return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> }
>
> +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject *kobj,
> + struct bin_attribute *bin_attr,
> + char *buf, loff_t pos, size_t count)
> +{
> + struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> +
> + if (!fw_cfg_dma_enabled())
> + return -ENOTSUPP;
> +
> + if (pos > entry->f.size)
> + return -EINVAL;
> +
> + if (count > entry->f.size - pos)
> + count = entry->f.size - pos;
> +
> + return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> +}
> +
> static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> - .attr = { .name = "raw", .mode = S_IRUSR },
> + .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
> .read = fw_cfg_sysfs_read_raw,
> + .write = fw_cfg_sysfs_write_raw,
> };
>
> /*
> --
> 2.14.1.146.gd35faa819
Thanks.
HATAYAMA, Daisuke
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
2017-10-30 11:07 ` [Qemu-devel] " Hatayama, Daisuke
@ 2017-10-30 16:19 ` Michael S. Tsirkin
-1 siblings, 0 replies; 9+ messages in thread
From: Michael S. Tsirkin @ 2017-10-30 16:19 UTC (permalink / raw)
To: Hatayama, Daisuke
Cc: 'marcandre.lureau@redhat.com', 'somlo@cmu.edu',
linux-kernel, 'qemu-devel@nongnu.org'
On Mon, Oct 30, 2017 at 11:07:20AM +0000, Hatayama, Daisuke wrote:
> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> >
> > Since qemu 2.9, DMA write operations are allowed. However, usage of this
> > interface from kernel or user-space is strongly discouraged by the
> > maintainers. This patch is meant for experimentations for now.
> >
>
> Could you (or maintainers?) tell me how experimental the DMA write
> operations from kernel are?
>
> From some technical reason?
> Or simply there has not been enough test yet so far?
The concern is security, talking from userspace to hypervisor
might become a trivial DOS vector.
If there's need for a specific entry to be accessible from userspace,
I'd rather white-list it.
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> > drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
> > 1 file changed, 20 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> > index 54b569da3257..e2f2ad1c9c0c 100644
> > --- a/drivers/firmware/qemu_fw_cfg.c
> > +++ b/drivers/firmware/qemu_fw_cfg.c
> > @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
> > return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> > }
> >
> > +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject *kobj,
> > + struct bin_attribute *bin_attr,
> > + char *buf, loff_t pos, size_t count)
> > +{
> > + struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > +
> > + if (!fw_cfg_dma_enabled())
> > + return -ENOTSUPP;
> > +
> > + if (pos > entry->f.size)
> > + return -EINVAL;
> > +
> > + if (count > entry->f.size - pos)
> > + count = entry->f.size - pos;
> > +
> > + return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> > +}
> > +
> > static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> > - .attr = { .name = "raw", .mode = S_IRUSR },
> > + .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
> > .read = fw_cfg_sysfs_read_raw,
> > + .write = fw_cfg_sysfs_write_raw,
> > };
> >
> > /*
> > --
> > 2.14.1.146.gd35faa819
>
> Thanks.
> HATAYAMA, Daisuke
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
@ 2017-10-30 16:19 ` Michael S. Tsirkin
0 siblings, 0 replies; 9+ messages in thread
From: Michael S. Tsirkin @ 2017-10-30 16:19 UTC (permalink / raw)
To: Hatayama, Daisuke
Cc: 'marcandre.lureau@redhat.com', 'somlo@cmu.edu',
linux-kernel, 'qemu-devel@nongnu.org'
On Mon, Oct 30, 2017 at 11:07:20AM +0000, Hatayama, Daisuke wrote:
> > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> >
> > Since qemu 2.9, DMA write operations are allowed. However, usage of this
> > interface from kernel or user-space is strongly discouraged by the
> > maintainers. This patch is meant for experimentations for now.
> >
>
> Could you (or maintainers?) tell me how experimental the DMA write
> operations from kernel are?
>
> From some technical reason?
> Or simply there has not been enough test yet so far?
The concern is security, talking from userspace to hypervisor
might become a trivial DOS vector.
If there's need for a specific entry to be accessible from userspace,
I'd rather white-list it.
> > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ---
> > drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
> > 1 file changed, 20 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
> > index 54b569da3257..e2f2ad1c9c0c 100644
> > --- a/drivers/firmware/qemu_fw_cfg.c
> > +++ b/drivers/firmware/qemu_fw_cfg.c
> > @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
> > return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> > }
> >
> > +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject *kobj,
> > + struct bin_attribute *bin_attr,
> > + char *buf, loff_t pos, size_t count)
> > +{
> > + struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > +
> > + if (!fw_cfg_dma_enabled())
> > + return -ENOTSUPP;
> > +
> > + if (pos > entry->f.size)
> > + return -EINVAL;
> > +
> > + if (count > entry->f.size - pos)
> > + count = entry->f.size - pos;
> > +
> > + return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> > +}
> > +
> > static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> > - .attr = { .name = "raw", .mode = S_IRUSR },
> > + .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
> > .read = fw_cfg_sysfs_read_raw,
> > + .write = fw_cfg_sysfs_write_raw,
> > };
> >
> > /*
> > --
> > 2.14.1.146.gd35faa819
>
> Thanks.
> HATAYAMA, Daisuke
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* RE: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
2017-10-30 16:19 ` [Qemu-devel] " Michael S. Tsirkin
@ 2017-10-31 9:55 ` Hatayama, Daisuke
-1 siblings, 0 replies; 9+ messages in thread
From: Hatayama, Daisuke @ 2017-10-31 9:55 UTC (permalink / raw)
To: 'Michael S. Tsirkin'
Cc: 'marcandre.lureau@redhat.com', 'somlo@cmu.edu',
linux-kernel, 'qemu-devel@nongnu.org'
> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org
> [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Michael S. Tsirkin
> Sent: Tuesday, October 31, 2017 1:19 AM
> To: Hatayama, Daisuke <d.hatayama@jp.fujitsu.com>
> Cc: 'marcandre.lureau@redhat.com' <marcandre.lureau@redhat.com>;
> 'somlo@cmu.edu' <somlo@cmu.edu>; linux-kernel@vger.kernel.org;
> 'qemu-devel@nongnu.org' <qemu-devel@nongnu.org>
> Subject: Re: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
>
> On Mon, Oct 30, 2017 at 11:07:20AM +0000, Hatayama, Daisuke wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >
> > > Since qemu 2.9, DMA write operations are allowed. However, usage of this
> > > interface from kernel or user-space is strongly discouraged by the
> > > maintainers. This patch is meant for experimentations for now.
> > >
> >
> > Could you (or maintainers?) tell me how experimental the DMA write
> > operations from kernel are?
> >
> > From some technical reason?
> > Or simply there has not been enough test yet so far?
>
> The concern is security, talking from userspace to hypervisor
> might become a trivial DOS vector.
>
> If there's need for a specific entry to be accessible from userspace,
> I'd rather white-list it.
>
Thanks for the explanation.
If so, I guess the white-list is done in userspace qemu side,
and no additional change would be needed for this kernel-side patch set for the white-list feature.
Is this understanding correct?
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > > drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
> > > 1 file changed, 20 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/firmware/qemu_fw_cfg.c
> b/drivers/firmware/qemu_fw_cfg.c
> > > index 54b569da3257..e2f2ad1c9c0c 100644
> > > --- a/drivers/firmware/qemu_fw_cfg.c
> > > +++ b/drivers/firmware/qemu_fw_cfg.c
> > > @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp,
> struct kobject *kobj,
> > > return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> > > }
> > >
> > > +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject
> *kobj,
> > > + struct bin_attribute *bin_attr,
> > > + char *buf, loff_t pos, size_t count)
> > > +{
> > > + struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > > +
> > > + if (!fw_cfg_dma_enabled())
> > > + return -ENOTSUPP;
> > > +
> > > + if (pos > entry->f.size)
> > > + return -EINVAL;
> > > +
> > > + if (count > entry->f.size - pos)
> > > + count = entry->f.size - pos;
> > > +
> > > + return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> > > +}
> > > +
> > > static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> > > - .attr = { .name = "raw", .mode = S_IRUSR },
> > > + .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
> > > .read = fw_cfg_sysfs_read_raw,
> > > + .write = fw_cfg_sysfs_write_raw,
> > > };
> > >
> > > /*
> > > --
> > > 2.14.1.146.gd35faa819
> >
> > Thanks.
> > HATAYAMA, Daisuke
> >
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
@ 2017-10-31 9:55 ` Hatayama, Daisuke
0 siblings, 0 replies; 9+ messages in thread
From: Hatayama, Daisuke @ 2017-10-31 9:55 UTC (permalink / raw)
To: 'Michael S. Tsirkin'
Cc: 'marcandre.lureau@redhat.com', 'somlo@cmu.edu',
linux-kernel, 'qemu-devel@nongnu.org'
> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org
> [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Michael S. Tsirkin
> Sent: Tuesday, October 31, 2017 1:19 AM
> To: Hatayama, Daisuke <d.hatayama@jp.fujitsu.com>
> Cc: 'marcandre.lureau@redhat.com' <marcandre.lureau@redhat.com>;
> 'somlo@cmu.edu' <somlo@cmu.edu>; linux-kernel@vger.kernel.org;
> 'qemu-devel@nongnu.org' <qemu-devel@nongnu.org>
> Subject: Re: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
>
> On Mon, Oct 30, 2017 at 11:07:20AM +0000, Hatayama, Daisuke wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > >
> > > Since qemu 2.9, DMA write operations are allowed. However, usage of this
> > > interface from kernel or user-space is strongly discouraged by the
> > > maintainers. This patch is meant for experimentations for now.
> > >
> >
> > Could you (or maintainers?) tell me how experimental the DMA write
> > operations from kernel are?
> >
> > From some technical reason?
> > Or simply there has not been enough test yet so far?
>
> The concern is security, talking from userspace to hypervisor
> might become a trivial DOS vector.
>
> If there's need for a specific entry to be accessible from userspace,
> I'd rather white-list it.
>
Thanks for the explanation.
If so, I guess the white-list is done in userspace qemu side,
and no additional change would be needed for this kernel-side patch set for the white-list feature.
Is this understanding correct?
> > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > ---
> > > drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
> > > 1 file changed, 20 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/firmware/qemu_fw_cfg.c
> b/drivers/firmware/qemu_fw_cfg.c
> > > index 54b569da3257..e2f2ad1c9c0c 100644
> > > --- a/drivers/firmware/qemu_fw_cfg.c
> > > +++ b/drivers/firmware/qemu_fw_cfg.c
> > > @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp,
> struct kobject *kobj,
> > > return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> > > }
> > >
> > > +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject
> *kobj,
> > > + struct bin_attribute *bin_attr,
> > > + char *buf, loff_t pos, size_t count)
> > > +{
> > > + struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > > +
> > > + if (!fw_cfg_dma_enabled())
> > > + return -ENOTSUPP;
> > > +
> > > + if (pos > entry->f.size)
> > > + return -EINVAL;
> > > +
> > > + if (count > entry->f.size - pos)
> > > + count = entry->f.size - pos;
> > > +
> > > + return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> > > +}
> > > +
> > > static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> > > - .attr = { .name = "raw", .mode = S_IRUSR },
> > > + .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
> > > .read = fw_cfg_sysfs_read_raw,
> > > + .write = fw_cfg_sysfs_write_raw,
> > > };
> > >
> > > /*
> > > --
> > > 2.14.1.146.gd35faa819
> >
> > Thanks.
> > HATAYAMA, Daisuke
> >
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
2017-10-31 9:55 ` [Qemu-devel] " Hatayama, Daisuke
@ 2017-10-31 17:06 ` Michael S. Tsirkin
-1 siblings, 0 replies; 9+ messages in thread
From: Michael S. Tsirkin @ 2017-10-31 17:06 UTC (permalink / raw)
To: Hatayama, Daisuke
Cc: 'marcandre.lureau@redhat.com', 'somlo@cmu.edu',
linux-kernel, 'qemu-devel@nongnu.org'
On Tue, Oct 31, 2017 at 09:55:39AM +0000, Hatayama, Daisuke wrote:
>
>
> > -----Original Message-----
> > From: linux-kernel-owner@vger.kernel.org
> > [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Michael S. Tsirkin
> > Sent: Tuesday, October 31, 2017 1:19 AM
> > To: Hatayama, Daisuke <d.hatayama@jp.fujitsu.com>
> > Cc: 'marcandre.lureau@redhat.com' <marcandre.lureau@redhat.com>;
> > 'somlo@cmu.edu' <somlo@cmu.edu>; linux-kernel@vger.kernel.org;
> > 'qemu-devel@nongnu.org' <qemu-devel@nongnu.org>
> > Subject: Re: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
> >
> > On Mon, Oct 30, 2017 at 11:07:20AM +0000, Hatayama, Daisuke wrote:
> > > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > >
> > > > Since qemu 2.9, DMA write operations are allowed. However, usage of this
> > > > interface from kernel or user-space is strongly discouraged by the
> > > > maintainers. This patch is meant for experimentations for now.
> > > >
> > >
> > > Could you (or maintainers?) tell me how experimental the DMA write
> > > operations from kernel are?
> > >
> > > From some technical reason?
> > > Or simply there has not been enough test yet so far?
> >
> > The concern is security, talking from userspace to hypervisor
> > might become a trivial DOS vector.
> >
> > If there's need for a specific entry to be accessible from userspace,
> > I'd rather white-list it.
> >
>
> Thanks for the explanation.
>
> If so, I guess the white-list is done in userspace qemu side,
> and no additional change would be needed for this kernel-side patch set for the white-list feature.
> Is this understanding correct?
No - host side has no idea whether it's guest userspace or
kernel initiating the access.
> > > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > ---
> > > > drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
> > > > 1 file changed, 20 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/firmware/qemu_fw_cfg.c
> > b/drivers/firmware/qemu_fw_cfg.c
> > > > index 54b569da3257..e2f2ad1c9c0c 100644
> > > > --- a/drivers/firmware/qemu_fw_cfg.c
> > > > +++ b/drivers/firmware/qemu_fw_cfg.c
> > > > @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp,
> > struct kobject *kobj,
> > > > return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> > > > }
> > > >
> > > > +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject
> > *kobj,
> > > > + struct bin_attribute *bin_attr,
> > > > + char *buf, loff_t pos, size_t count)
> > > > +{
> > > > + struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > > > +
> > > > + if (!fw_cfg_dma_enabled())
> > > > + return -ENOTSUPP;
> > > > +
> > > > + if (pos > entry->f.size)
> > > > + return -EINVAL;
> > > > +
> > > > + if (count > entry->f.size - pos)
> > > > + count = entry->f.size - pos;
> > > > +
> > > > + return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> > > > +}
> > > > +
> > > > static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> > > > - .attr = { .name = "raw", .mode = S_IRUSR },
> > > > + .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
> > > > .read = fw_cfg_sysfs_read_raw,
> > > > + .write = fw_cfg_sysfs_write_raw,
> > > > };
> > > >
> > > > /*
> > > > --
> > > > 2.14.1.146.gd35faa819
> > >
> > > Thanks.
> > > HATAYAMA, Daisuke
> > >
> >
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [Qemu-devel] [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
@ 2017-10-31 17:06 ` Michael S. Tsirkin
0 siblings, 0 replies; 9+ messages in thread
From: Michael S. Tsirkin @ 2017-10-31 17:06 UTC (permalink / raw)
To: Hatayama, Daisuke
Cc: 'marcandre.lureau@redhat.com', 'somlo@cmu.edu',
linux-kernel, 'qemu-devel@nongnu.org'
On Tue, Oct 31, 2017 at 09:55:39AM +0000, Hatayama, Daisuke wrote:
>
>
> > -----Original Message-----
> > From: linux-kernel-owner@vger.kernel.org
> > [mailto:linux-kernel-owner@vger.kernel.org] On Behalf Of Michael S. Tsirkin
> > Sent: Tuesday, October 31, 2017 1:19 AM
> > To: Hatayama, Daisuke <d.hatayama@jp.fujitsu.com>
> > Cc: 'marcandre.lureau@redhat.com' <marcandre.lureau@redhat.com>;
> > 'somlo@cmu.edu' <somlo@cmu.edu>; linux-kernel@vger.kernel.org;
> > 'qemu-devel@nongnu.org' <qemu-devel@nongnu.org>
> > Subject: Re: [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
> >
> > On Mon, Oct 30, 2017 at 11:07:20AM +0000, Hatayama, Daisuke wrote:
> > > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > >
> > > > Since qemu 2.9, DMA write operations are allowed. However, usage of this
> > > > interface from kernel or user-space is strongly discouraged by the
> > > > maintainers. This patch is meant for experimentations for now.
> > > >
> > >
> > > Could you (or maintainers?) tell me how experimental the DMA write
> > > operations from kernel are?
> > >
> > > From some technical reason?
> > > Or simply there has not been enough test yet so far?
> >
> > The concern is security, talking from userspace to hypervisor
> > might become a trivial DOS vector.
> >
> > If there's need for a specific entry to be accessible from userspace,
> > I'd rather white-list it.
> >
>
> Thanks for the explanation.
>
> If so, I guess the white-list is done in userspace qemu side,
> and no additional change would be needed for this kernel-side patch set for the white-list feature.
> Is this understanding correct?
No - host side has no idea whether it's guest userspace or
kernel initiating the access.
> > > > Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> > > > ---
> > > > drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
> > > > 1 file changed, 20 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/firmware/qemu_fw_cfg.c
> > b/drivers/firmware/qemu_fw_cfg.c
> > > > index 54b569da3257..e2f2ad1c9c0c 100644
> > > > --- a/drivers/firmware/qemu_fw_cfg.c
> > > > +++ b/drivers/firmware/qemu_fw_cfg.c
> > > > @@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp,
> > struct kobject *kobj,
> > > > return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
> > > > }
> > > >
> > > > +static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject
> > *kobj,
> > > > + struct bin_attribute *bin_attr,
> > > > + char *buf, loff_t pos, size_t count)
> > > > +{
> > > > + struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
> > > > +
> > > > + if (!fw_cfg_dma_enabled())
> > > > + return -ENOTSUPP;
> > > > +
> > > > + if (pos > entry->f.size)
> > > > + return -EINVAL;
> > > > +
> > > > + if (count > entry->f.size - pos)
> > > > + count = entry->f.size - pos;
> > > > +
> > > > + return fw_cfg_write_blob(entry->f.select, buf, pos, count);
> > > > +}
> > > > +
> > > > static struct bin_attribute fw_cfg_sysfs_attr_raw = {
> > > > - .attr = { .name = "raw", .mode = S_IRUSR },
> > > > + .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
> > > > .read = fw_cfg_sysfs_read_raw,
> > > > + .write = fw_cfg_sysfs_write_raw,
> > > > };
> > > >
> > > > /*
> > > > --
> > > > 2.14.1.146.gd35faa819
> > >
> > > Thanks.
> > > HATAYAMA, Daisuke
> > >
> >
>
^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs
2017-09-22 13:24 [PATCH v3 0/5] fw_cfg: add DMA operations & etc/vmcoreinfo support marcandre.lureau
@ 2017-09-22 13:24 ` marcandre.lureau
0 siblings, 0 replies; 9+ messages in thread
From: marcandre.lureau @ 2017-09-22 13:24 UTC (permalink / raw)
To: linux-kernel; +Cc: somlo, qemu-devel, mst, Marc-André Lureau
From: Marc-André Lureau <marcandre.lureau@redhat.com>
Since qemu 2.9, DMA write operations are allowed. However, usage of this
interface from kernel or user-space is strongly discouraged by the
maintainers. This patch is meant for experimentations for now.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
drivers/firmware/qemu_fw_cfg.c | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 54b569da3257..e2f2ad1c9c0c 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -524,9 +524,28 @@ static ssize_t fw_cfg_sysfs_read_raw(struct file *filp, struct kobject *kobj,
return fw_cfg_read_blob(entry->f.select, buf, pos, count, true);
}
+static ssize_t fw_cfg_sysfs_write_raw(struct file *filp, struct kobject *kobj,
+ struct bin_attribute *bin_attr,
+ char *buf, loff_t pos, size_t count)
+{
+ struct fw_cfg_sysfs_entry *entry = to_entry(kobj);
+
+ if (!fw_cfg_dma_enabled())
+ return -ENOTSUPP;
+
+ if (pos > entry->f.size)
+ return -EINVAL;
+
+ if (count > entry->f.size - pos)
+ count = entry->f.size - pos;
+
+ return fw_cfg_write_blob(entry->f.select, buf, pos, count);
+}
+
static struct bin_attribute fw_cfg_sysfs_attr_raw = {
- .attr = { .name = "raw", .mode = S_IRUSR },
+ .attr = { .name = "raw", .mode = S_IRUSR | S_IWUSR },
.read = fw_cfg_sysfs_read_raw,
+ .write = fw_cfg_sysfs_write_raw,
};
/*
--
2.14.1.146.gd35faa819
^ permalink raw reply related [flat|nested] 9+ messages in thread
end of thread, other threads:[~2017-10-31 17:06 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-10-30 11:07 [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs Hatayama, Daisuke
2017-10-30 11:07 ` [Qemu-devel] " Hatayama, Daisuke
2017-10-30 16:19 ` Michael S. Tsirkin
2017-10-30 16:19 ` [Qemu-devel] " Michael S. Tsirkin
2017-10-31 9:55 ` Hatayama, Daisuke
2017-10-31 9:55 ` [Qemu-devel] " Hatayama, Daisuke
2017-10-31 17:06 ` Michael S. Tsirkin
2017-10-31 17:06 ` [Qemu-devel] " Michael S. Tsirkin
-- strict thread matches above, loose matches on Subject: below --
2017-09-22 13:24 [PATCH v3 0/5] fw_cfg: add DMA operations & etc/vmcoreinfo support marcandre.lureau
2017-09-22 13:24 ` [PATCH v3 5/5] RFC: fw_cfg: add DMA write operation in sysfs marcandre.lureau
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