On Wed, 29 Jun 2022, Mark Yacoub <markyacoub@xxxxxxxxxxxx> wrote: > Hi Jani, let me know if you need more info or more changes are needed. Thanks! Sorry, I really haven't had the time to think this through. At a glance, I'm unable to find the hdcp key property that this is being used with. Am I missing something? Where's that created and used in the kernel? BR, Jani. > > On Wed, May 25, 2022 at 3:31 PM Mark Yacoub <markyacoub@xxxxxxxxxxxx> wrote: >> >> Hi Jani, thanks for your review. I got all the user space >> implementation ready to see it in context. >> >> libdrm patch to wrap this functionality: >> https://www.spinics.net/lists/dri-devel/msg347318.html >> >> Chromium user space implementation making direct use of the new prop flag: >> crrev.com/c/3655850 >> The first call made to such functionality is in >> https://chromium-review.googlesource.com/c/chromium/src/+/3655850/2/ui/display/manager/content_protection_key_manager.cc#137 >> where the call stack flows to the libdrm wrapper call at >> https://chromium-review.googlesource.com/c/chromium/src/+/3655850/2/ui/ozone/platform/drm/gpu/drm_display.cc#203 >> >> I also wrote an IGT test to verify the intended behavior: >> https://patchwork.freedesktop.org/patch/487331/?series=104373&rev=1 >> >> Let me know if I would need to update the commit message with any of >> the aforementioned context. >> >> Thanks! >> -Mark Yacoub >> >> On Tue, May 17, 2022 at 3:53 AM Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx> wrote: >> > >> > On Tue, 10 May 2022, Mark Yacoub <markyacoub@xxxxxxxxxxxx> wrote: >> > > [Why] >> > > User space might need to inject data into the kernel without allowing it >> > > to be read again by any user space. >> > > An example of where this is particularly useful is secret keys fetched >> > > by user space and injected into the kernel to enable content protection. >> > >> > I think we're going to need more than an example in the commit >> > message. See Documentation/gpu/drm-uapi.rst. >> > >> > BR, >> > Jani. >> > >> > >> > > >> > > [How] >> > > Create a DRM_MODE_CREATE_BLOB_WRITE_ONLY flag used by user space to >> > > create a blob and mark the blob as write only. >> > > On reading back the blob, data will be not be copied if it's a write >> > > only blob >> > > >> > > Signed-off-by: Mark Yacoub <markyacoub@xxxxxxxxxxxx> >> > > >> > > --- >> > > drivers/gpu/drm/drm_property.c | 3 ++- >> > > include/drm/drm_property.h | 2 ++ >> > > include/uapi/drm/drm_mode.h | 6 ++++++ >> > > 3 files changed, 10 insertions(+), 1 deletion(-) >> > > >> > > diff --git a/drivers/gpu/drm/drm_property.c b/drivers/gpu/drm/drm_property.c >> > > index dfec479830e4..afedf7109d00 100644 >> > > --- a/drivers/gpu/drm/drm_property.c >> > > +++ b/drivers/gpu/drm/drm_property.c >> > > @@ -765,7 +765,7 @@ int drm_mode_getblob_ioctl(struct drm_device *dev, >> > > if (!blob) >> > > return -ENOENT; >> > > >> > > - if (out_resp->length == blob->length) { >> > > + if (out_resp->length == blob->length && !blob->is_write_only) { >> > > if (copy_to_user(u64_to_user_ptr(out_resp->data), >> > > blob->data, >> > > blob->length)) { >> > > @@ -800,6 +800,7 @@ int drm_mode_createblob_ioctl(struct drm_device *dev, >> > > ret = -EFAULT; >> > > goto out_blob; >> > > } >> > > + blob->is_write_only = out_resp->flags & DRM_MODE_CREATE_BLOB_WRITE_ONLY; >> > > >> > > /* Dropping the lock between create_blob and our access here is safe >> > > * as only the same file_priv can remove the blob; at this point, it is >> > > diff --git a/include/drm/drm_property.h b/include/drm/drm_property.h >> > > index 65bc9710a470..700782f021b9 100644 >> > > --- a/include/drm/drm_property.h >> > > +++ b/include/drm/drm_property.h >> > > @@ -205,6 +205,7 @@ struct drm_property { >> > > * &drm_mode_config.property_blob_list. >> > > * @head_file: entry on the per-file blob list in &drm_file.blobs list. >> > > * @length: size of the blob in bytes, invariant over the lifetime of the object >> > > + * @is_write_only: user space can't read the blob data. >> > > * @data: actual data, embedded at the end of this structure >> > > * >> > > * Blobs are used to store bigger values than what fits directly into the 64 >> > > @@ -219,6 +220,7 @@ struct drm_property_blob { >> > > struct list_head head_global; >> > > struct list_head head_file; >> > > size_t length; >> > > + bool is_write_only; >> > > void *data; >> > > }; >> > > >> > > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h >> > > index 0a0d56a6158e..de192d3813e9 100644 >> > > --- a/include/uapi/drm/drm_mode.h >> > > +++ b/include/uapi/drm/drm_mode.h >> > > @@ -1107,6 +1107,9 @@ struct drm_format_modifier { >> > > __u64 modifier; >> > > }; >> > > >> > > +#define DRM_MODE_CREATE_BLOB_WRITE_ONLY \ >> > > + (1 << 0) /* data of the blob can't be read by user space */ >> > > + >> > > /** >> > > * struct drm_mode_create_blob - Create New blob property >> > > * >> > > @@ -1120,6 +1123,9 @@ struct drm_mode_create_blob { >> > > __u32 length; >> > > /** @blob_id: Return: new property ID. */ >> > > __u32 blob_id; >> > > + /** Flags for special handling. */ >> > > + __u32 flags; >> > > + __u32 pad; >> > > }; >> > > >> > > /** >> > >> > -- >> > Jani Nikula, Intel Open Source Graphics Center -- Jani Nikula, Intel Open Source Graphics Center
