From nobody Sun May 10 09:55:06 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DCE62C433EF for ; Tue, 10 May 2022 19:08:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245674AbiEJTIi (ORCPT ); Tue, 10 May 2022 15:08:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233947AbiEJTIf (ORCPT ); Tue, 10 May 2022 15:08:35 -0400 Received: from mail-qk1-x72f.google.com (mail-qk1-x72f.google.com [IPv6:2607:f8b0:4864:20::72f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D95001FD870 for ; Tue, 10 May 2022 12:08:32 -0700 (PDT) Received: by mail-qk1-x72f.google.com with SMTP id j6so66271qkp.9 for ; Tue, 10 May 2022 12:08:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=4jRHmDRiTYtUVm3F2TV/cnHc4gTZpNzxAskWEMeHjb0=; b=ijenj0F+shWYlWKOKoPsXSieljDL6aNFFf7PrQL/Ej9MqigLI+I6PoyAgdCgspqEi+ KaYJt1YKojvXmOyLRcurUzYjQNByqWE5QGLU4tFziqofD8iwTfE++UmBGqlM9vGMECpc kSbky1WTM4ldI7ijbwPOiqKJtJFWLDuHt7BmA= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=4jRHmDRiTYtUVm3F2TV/cnHc4gTZpNzxAskWEMeHjb0=; b=KUtPDJK5CATNP7aU6csTOuLV3Gt2na4kkPXLCPfO3eHz0f++9oDwshFs2NTKF6+a0J 67kgQdlDu4oY1aYg4QVks4yv7LBaBuoB8uNcbgRgSxwCiacd+vpzkJtkGLAApKvojXMK V8edlkM9pEKKhufuaUHJ/JBSW0UHTsp3q+IK+5NkEvLeCCdBn+HvcOYSQJxnuJ6amowG vyC4Y4iHRzk9roIYAub9Vps+bAwbqVmJzVqLGmD3sTDhvx8gItloqT82lzfH9jg5xt7S OQvEyIzZ2SfWukr/ylVpaH75S2dKjLoELszzSLDz/Rl829vOFZ4Fr+rG4GT/ajSR+vGq iZBw== X-Gm-Message-State: AOAM530FJIA7bRu43EKjNGK/0FkH7YAJdzsZbmn9RNI0WgWFWzIJ9Y70 3u+XUFaeC8wFw7VJSACBqTOMvQ== X-Google-Smtp-Source: ABdhPJxhZMWvFMdDp5OOtpLRcQsMnI7cLWD8+vbJIItoETMs2u7GJzxM3szzCaPCWDdg9jrbJat/WA== X-Received: by 2002:a05:620a:4083:b0:6a0:9d07:5127 with SMTP id f3-20020a05620a408300b006a09d075127mr7404455qko.51.1652209711777; Tue, 10 May 2022 12:08:31 -0700 (PDT) Received: from markyacoub.nyc.corp.google.com ([2620:0:1003:314:141d:f589:29f6:2a25]) by smtp.gmail.com with ESMTPSA id x8-20020ac87a88000000b002f39b99f6b1sm9590931qtr.75.2022.05.10.12.08.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 10 May 2022 12:08:31 -0700 (PDT) From: Mark Yacoub Cc: seanpaul@chromium.org, markyacoub@google.com, markyacoub@chromium.org, Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Daniel Vetter , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH] drm: Create support for Write-Only property blob Date: Tue, 10 May 2022 15:08:21 -0400 Message-Id: <20220510190823.1552920-1-markyacoub@chromium.org> X-Mailer: git-send-email 2.36.0.512.ge40c2bad7a-goog MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable To: unlisted-recipients:; (no To-header on input) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" [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. [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 --- 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; =20 - if (out_resp->length =3D=3D blob->length) { + if (out_resp->length =3D=3D 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 =3D -EFAULT; goto out_blob; } + blob->is_write_only =3D out_resp->flags & DRM_MODE_CREATE_BLOB_WRITE_ONLY; =20 /* 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; }; =20 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; }; =20 +#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; }; =20 /** --=20 2.36.0.512.ge40c2bad7a-goog