Name KHR_robustness Name Strings GL_KHR_robustness Contributors Daniel Koch, NVIDIA Nicolas Capens, TransGaming Contributors to ARB_robustness Contact Jon Leech (oddhack 'at' sonic.net) Greg Roth, NVIDIA (groth 'at' nvidia.com) Notice Copyright (c) 2012-2014 The Khronos Group Inc. Copyright terms at http://www.khronos.org/registry/speccopyright.html Specification Update Policy Khronos-approved extension specifications are updated in response to issues and bugs prioritized by the Khronos OpenGL and OpenGL ES Working Groups. For extensions which have been promoted to a core Specification, fixes will first appear in the latest version of that core Specification, and will eventually be backported to the extension document. This policy is described in more detail at https://www.khronos.org/registry/OpenGL/docs/update_policy.php Status Complete. Approved by the OpenGL ES Working Group on June 25, 2014. Approved by the ARB on June 26, 2014. Ratified by the Khronos Board of Promoters on August 7, 2014. Version Version 11, August 21, 2014 Number ARB Extension #170 OpenGL ES Extension #190 Dependencies OpenGL ES 2.0 or OpenGL 3.2 are required. Some features of this extension are supported by OpenGL ES only if OpenGL ES 3.0 or later is supported. EGL_EXT_create_context_robustness is used to determine if a context implementing this extension supports robust buffer access, and if it supports reset notification. This extension is written against the OpenGL ES 3.1 Specification (version of June 4, 2014) and the OpenGL ES 3.10.3 Shading Language Specification (version of June 6, 2014). Overview Several recent trends in how OpenGL ES integrates into modern computer systems have created new requirements for robustness and security for GL rendering contexts. Additionally GPU architectures now support hardware fault detection; for example, video memory supporting ECC (error correcting codes) and error detection. GL contexts should be capable of recovering from hardware faults such as uncorrectable memory errors. Along with recovery from such hardware faults, the recovery mechanism can also allow recovery from video memory access exceptions and system software failures. System software failures can be due to device changes or driver failures. GL queries that return (write) some number of bytes to a buffer indicated by a pointer parameter introduce risk of buffer overflows that might be exploitable by malware. To address this, queries with return value sizes that are not expressed directly by the parameters to the query itself are given additional API functions with an additional parameter that specifies the number of bytes in the buffer and never writing bytes beyond that limit. This is particularly useful for multi-threaded usage of GL contexts in a "share group" where one context can change objects in ways that can cause buffer overflows for another context's GL queries. The original ARB_vertex_buffer_object extension includes an issue that explicitly states program termination is allowed when out-of-bounds vertex buffer object fetches occur. Modern graphics hardware is capable of well-defined behavior in the case of out-of- bounds vertex buffer object fetches. Older hardware may require extra checks to enforce well-defined (and termination free) behavior, but this expense is warranted when processing potentially untrusted content. The intent of this extension is to address some specific robustness goals: * For all existing GL queries, provide additional "safe" APIs that limit data written to user pointers to a buffer size in bytes that is an explicit additional parameter of the query. * Provide a mechanism for a GL application to learn about graphics resets that affect the context. When a graphics reset occurs, the GL context becomes unusable and the application must create a new context to continue operation. Detecting a graphics reset happens through an inexpensive query. * Define behavior of OpenGL calls made after a graphics reset. * Provide an enable to guarantee that out-of-bounds buffer object accesses by the GPU will have deterministic behavior and preclude application instability or termination due to an incorrect buffer access. Such accesses include vertex buffer fetches of attributes and indices, and indexed reads of uniforms or parameters from buffers. New Procedures and Functions NOTE: when implemented in an OpenGL ES context, all entry points defined by this extension must have a "KHR" suffix. When implemented in an OpenGL context, all entry points must have NO suffix, as shown below. enum GetGraphicsResetStatus(); void ReadnPixels(int x, int y, sizei width, sizei height, enum format, enum type, sizei bufSize, void *data); void GetnUniformfv(uint program, int location, sizei bufSize, float *params); void GetnUniformiv(uint program, int location, sizei bufSize, int *params); void GetnUniformuiv(uint program, int location, sizei bufSize, uint *params); New Tokens NOTE: when implemented in an OpenGL ES context, all tokens defined by this extension must have a "_KHR" suffix. When implemented in an OpenGL context, all tokens must have NO suffix, as described below. Returned by GetGraphicsResetStatus: NO_ERROR 0x0000 GUILTY_CONTEXT_RESET 0x8253 INNOCENT_CONTEXT_RESET 0x8254 UNKNOWN_CONTEXT_RESET 0x8255 Accepted by the parameter of GetBooleanv, GetIntegerv, and GetFloatv: CONTEXT_ROBUST_ACCESS 0x90F3 RESET_NOTIFICATION_STRATEGY 0x8256 Returned by GetIntegerv and related simple queries when is RESET_NOTIFICATION_STRATEGY : LOSE_CONTEXT_ON_RESET 0x8252 NO_RESET_NOTIFICATION 0x8261 Returned by GetError: CONTEXT_LOST 0x0507 Additions to the OpenGL ES 3.1 Specification Add to section 2.3.1 "Errors" in the bullet list of implicit errors for GL commands on p. 14, and modify the following paragraph: * If the GL context has been reset as a result of a previous GL command, or if the context is reset as a side effect of execution of a command, a CONTEXT_LOST error is generated. The Specification attempts to explicitly describe these implicit error conditions (with the exception of OUT_OF_MEMORY [fn2] and CONTEXT_LOST [fn3]) wherever they apply. However ... [fn3] CONTEXT_LOST is not described because it occurs for reasons not directly related to the affected commands, and applies to almost all GL commands. Add to table 2.3 "Summary of GL errors" on p. 15: Error Description Offending command ignored? ------------ ----------------------- -------------------------- CONTEXT_LOST Context has been lost Except as noted for and reset by the driver specific commands Add a new subsection 2.3.1rob after 2.3.1 "GL Errors", and renumber subsequent sections accordingly: 2.3.1rob "Graphics Reset Recovery" Certain events can result in a reset of the GL context. After such an event, it is referred to as a and is unusable for almost all purposes. Recovery requires creating a new context and recreating all relevant state from the lost context. The current status of the graphics reset state is returned by enum GetGraphicsResetStatus(); The value returned indicates if the GL context has been in a reset state at any point since the last call to GetGraphicsResetStatus: * NO_ERROR indicates that the GL context has not been in a reset state since the last call. * GUILTY_CONTEXT_RESET indicates that a reset has been detected that is attributable to the current GL context. * INNOCENT_CONTEXT_RESET indicates a reset has been detected that is not attributable to the current GL context. * UNKNOWN_CONTEXT_RESET indicates a detected graphics reset whose cause is unknown. If a reset status other than NO_ERROR is returned and subsequent calls return NO_ERROR, the context reset was encountered and completed. If a reset status is repeatedly returned, the context may be in the process of resetting. Reset notification behavior is determined at context creation time, and may be queried by calling GetIntegerv with the symbolic constant RESET_NOTIFICATION_STRATEGY. If the reset notification behavior is NO_RESET_NOTIFICATION, then the implementation will never deliver notification of reset events, and GetGraphicsResetStatus will always return NO_ERROR[fn1]. [fn1: In this case it is recommended that implementations should not allow loss of context state no matter what events occur. However, this is only a recommendation, and cannot be relied upon by applications.] If the behavior is LOSE_CONTEXT_ON_RESET, a graphics reset will result in a lost context and require creating a new context as described above. In this case GetGraphicsResetStatus will return an appropriate value from those described above. If a graphics reset notification occurs in a context, a notification must also occur in all other contexts which share objects with that context[fn2]. [fn2: The values returned by GetGraphicsResetStatus in the different contexts may differ.] After a graphics reset has occurred on a context, subsequent GL commands on that context (or any context which shares with that context) will generate a CONTEXT_LOST error. Such commands will not have side effects (in particular, they will not modify memory passed by pointer for query results), and may not block indefinitely or cause termination of the application. Exceptions to this behavior include: * GetError and GetGraphicsResetStatus behave normally following a graphics reset, so that the application can determine a reset has occurred, and when it is safe to destroy and recreate the context. * Any commands which might cause a polling application to block indefinitely will generate a CONTEXT_LOST error, but will also return a value indicating completion to the application. Such commands include: + GetSynciv with SYNC_STATUS ignores the other parameters and returns SIGNALED in . + GetQueryObjectuiv with QUERY_RESULT_AVAILABLE ignores the other parameters and returns TRUE in . Modify section 7.12 "Shader, Program, and Program Pipeline Queries" on p. 125 to add the GetnUniform* commands: The commands [enumerate existing GetUniform*v commands, then add] void GetnUniformfv(uint program, int location, sizei bufSize, float *params); void GetnUniformiv(uint program, int location, sizei bufSize, int *params); void GetnUniformuiv(uint program, int location, sizei bufSize, uint *params); return the value or values of the uniform at location of the default uniform block for program object in the array . The type of the uniform at determines the number of values returned. Calling GetnUniform*v ensures that no more than bytes are written into . Add to the Errors section for Get*Uniform* on p. 126: An INVALID_OPERATION error is generated by GetnUniform* if the buffer size required to store the requested data is greater than Add subsection 10.3.1.1rob prior to section 10.3.2 "Vertex Attribute Divisors" on p. 241: 10.3.1.1rob Robust Buffer Access Behavior Robust buffer access is enabled by creating a context with robust access enabled through the window system binding APIs. When enabled, indices within the element array that reference vertex data that lies outside the enabled attribute's vertex buffer object [for OpenGL ES] result in undefined values [for OpenGL] result in reading zero for the corresponding attributes, but cannot result in application failure. Robust buffer access behavior may be queried by calling GetIntegerv with the symbolic constant CONTEXT_ROBUST_ACCESS. Modify section 16.1.2 "ReadPixels" on p. 332 to add the ReadnPixels command: Pixels are read using void ReadPixels(int x, int y, sizei width, sizei height, enum format, enum type, void *data); void ReadnPixels(int x, int y, sizei width, sizei height, enum format, enum type, sizei bufSize, void *data); The arguments after and to ReadPixels ... are summarized in table 16.1. ReadnPixels behaves identically to ReadPixels except that it does not write more than bytes into . Add to the Errors section for ReadPixels and ReadnPixels: An INVALID_OPERATION error is generated by ReadnPixels if the buffer size required to store the requested data is greater than . Additions to The OpenGL ES Shading Language Specification, Version 3.10 Modify the first paragraph of section 4.1.9 "Arrays" on p. 30: Variables of the same type ... Undefined behavior results from indexing an array with a non-constant expression that is greater than or equal to the array size or less than 0. If robust buffer access is enabled (see section 10.3.1.1rob of the OpenGL ES 3.1 API Specification), such indexing must not result in abnormal program termination. The results are still undefined, but implementations are encouraged to produce zero values for such accesses. Arrays only have a single dimension ... Dependencies on OpenGL ES For implementations against OpenGL ES, if OpenGL ES 3.0 or a later version is not supported, remove all references to GetnUniformuiv and remove the exceptional behavior of GetSynciv and GetQueryObjectuiv for lost contexts. Interactions with EGL_EXT_create_context_robustness If the EGL window-system binding API is used to create a context, the EGL_EXT_create_context_robustness extension is supported, and the attribute EGL_CONTEXT_OPENGL_ROBUST_ACCESS_EXT is set to EGL_TRUE when eglCreateContext is called, the resulting context will perform robust buffer access as described above in section 10.3.1.1rob, and the CONTEXT_ROBUST_ACCESS query will return GL_TRUE. If the EGL window-system binding API is used to create a context and the EGL_EXT_create_context_robustness extension is supported, then the value of attribute EGL_CONTEXT_RESET_NOTIFICATION_STRATEGY_EXT determines the reset notification behavior and the value of RESET_NOTIFICATION_STRATEGY, as described in section 2.3.1rob. New Implementation Dependent State Get Value Type Get Command Minimum Value Description Sec. Attribute --------------------------- ---- ----------- ----------------- --------------------------- ----------- --------- CONTEXT_ROBUST_ACCESS B GetIntegerv - Robust access enabled 10.3.1.1rob - RESET_NOTIFICATION_STRATEGY Z_2 GetIntegerv See sec. 2.3.1rob Reset notification behavior 2.3.1rob - Issues (Issues 2-8 are identical to those in the base EXT_robustness extension). 1. What should this extension be called? RESOLVED: KHR_robustness This is just the OpenGL ES EXT_robustness extension (itself based on ARB_robustness) promoted to KHR status, with consistency with OpenGL 4.5 behavior and phrasing included. 2. How does this extension differ from Desktop GL's ARB_robustness? RESOLVED: Because EGL_EXT_create_context_robustness uses a separate attribute to enable robust buffer access, a corresponding query is added here. Also see issue 12. 3. Should we provide a context creation mechanism to enable this extension? RESOLVED. Yes. Currently, EGL_EXT_create_context_robustness provides this mechanism via two unique attributes. These attributes differ from those specified by KHR_create_context to allow for differences in what functionality those attributes define. 4. What can cause a graphics reset? Either user or implementor errors may result in a graphics reset. If the application attempts to perform a rendering that takes too long whether due to an infinite loop in a shader or even just a rendering operation that takes too long on the given hardware. Implementation errors may produce badly formed hardware commands. Memory access errors may result from user or implementor mistakes. On some systems, power management events such as system sleep, screen saver activation, or pre-emption may also context resets to occur. Any of these events may result in a graphics reset event that will be detectable by the mechanism described in this extension. 5. How should the application react to a reset context event? RESOLVED: For this extension, the application is expected to query the reset status until NO_ERROR is returned. If a reset is encountered, at least one *RESET* status will be returned. Once NO_ERROR is again encountered, the application can safely destroy the old context and create a new one. After a reset event, apps should not use a context for any purpose other than determining its reset status (using either GetError to identify a CONTEXT_LOST error, or GetGraphicsResetStatus()), and then destroying it. If a context receives a reset event, all other contexts in its share group will also receive reset events, and should be destroyed and recreated. Apps should be cautious in interpreting the GUILTY and INNOCENT reset statuses. These are guidelines to the immediate cause of a reset, but not guarantees of the ultimate cause. 6. If a graphics reset occurs in a shared context, what happens in shared contexts? RESOLVED: A reset in one context will result in a reset in all other contexts in its share group. 7. How can an application query for robust buffer access support, since this is now determined at context creation time? RESOLVED. The application can query the value of CONTEXT_ROBUST_ACCESS using GetIntegerv. If true, this functionality is enabled. 8. How is the reset notification behavior controlled? RESOLVED: Reset notification behavior is determined at context creation time using EGL/GLX/WGL/etc. mechanisms. In order that shared objects be handled predictably, a context cannot share with another context unless both have the same reset notification behavior. 9. How does this extension differ from EXT_robustness? RESOLVED: By adding the new CONTEXT_LOST error, removing support for ES 1.1 (for logistical reasons), and changing suffixes from EXT to KHR (for ES) or no suffix (for GL). 10. How should this extension be enabled via EGL? PROPOSED: Either by using EGL 1.5 context creation APIs (see section 3.7.1.5 of the EGL 1.5 spec), or EGL_EXT_create_context_robustness. This interaction will be noted in both the EGL 1.5 spec and the extension spec by allowing at least one, and possibly both of GL_EXT_robustness and GL_KHR_robustness to be supported by contexts created via these mechanisms. If a context supporting GL_KHR_robustness is created, it will optionally support GL_KHR_robust_buffer_access_behavior as well (see issue 5 of that extension). 11. What should the behavior of GL calls made after a context is lost be? This can be expected to occur when the context has been lost, but the app hasn't polled the reset status yet. RESOLVED: Set a new CONTEXT_LOST error on all GL calls (except GetError and GetGraphicsReset). DISCUSSION: GetError and GetGraphicsResetStatus must continue to work at least to the extent of their interactions with robustness features, so that apps can determine a context was lost and see the effect on other commands. Commands which might block indefinitely or cause the app to block indefinitely while polling are defined to return immediately, with values which should end a polling loop. Such commands include sync and query object queries for completion. Special handling of these commands is defined to return values which should not cause blocking, but also to generate the CONTEXT_LOST error. This is intended to deal well both with apps that are polling on a query value, and apps that may test for the error immediately after each command (such as debuggers). There has been no pushback against We believe there are no other commands requiring this special handling in the core API. ClientWaitSync and WaitSync were also proposed, but with the current language (which specifies that commands on a lost context may not block) should not need exceptional handling. REJECTED OPTIONS: A) GL will try to handle the call as best as possible. Depending on the call this may use GPU resources which may now have undefined contents. B) GL calls become no-ops. This would be like having a null-dispatch table installed when you don't have a current context. The problem with this approach is that any call that has return parameters won't fill them in and the application won't be able to detect that a value was not returned. REJECTED SUB-FEATURES: We discussed using OUT_OF_MEMORY or INVALID_OPERATION. Both are misleading and don't uniquely identify the problem as a runtime error out of scope of anything the app did. We discussed allowing all commands to have side effects in addition to generating CONTEXT_LOST, such as putting a "safe" value into return parameters. Without compelling reason to allow this behavior, it is cleaner to define the spec to leave results unchanged aside from the exceptional cases intended to prevent hanging on polling loops. 12. What changed in promoting OES_robustness to KHR_robustness? What remains to be done for consistency between GL and ES? DISCUSSION: The ARB agreed to support robustness and robust_buffer_access_behavior as a KHR extension, with the following chnages and issues to be resolved during the ratification period (none are IP-related): a) As was done for KHR_debug, the extension is defined to have KHR suffixes only in ES implementations. GL implementations do not have suffixes. This is so KHR_robustness can be used as a backwards-compatibility extension for OpenGL 4.5. b) Minor spec language tweaks were done for consistency with OpenGL 4.5, to eliminate redundancy. None are functional with the exception of a change in section 10.3.1.1rob, which imposes stronger requirements on out-of-bounds indexed attribute access for GL (returns zero) relative to ES (undefined return values). c) The ARB wants to add these commands to the extension, as defined in OpenGL 4.5. They would be only be supported in GL contexts: GetnUniformdv GetnTexImage GetnCompressedTexImage We do not think we need to add the compatibility-mode Getn* queries defined by ARB_robustness. d) OpenGL 4.5 exposes support for robustness by setting CONTEXT_FLAG_ROBUST_ACCESS_BIT in the CONTEXT_FLAGS query. ES (and this extension) expose it with the CONTEXT_ROBUST_ACCESS query. Jon proposes we resolve this by only defining the CONTEXT_FLAGS query for GL, but defining the CONTEXT_ROBUST_ACCESS query for both GL and ES, and aliasing the flag bit with the access boolean. This will result in minor changes to both GL 4.5 and this extension. e) This extension modifies the Shading Language specification in section 4.1.9 to restrict behavior of out of bounds array accesses. GLSL 4.50 has a considerably broader section 5.11 "Out-of-Bounds Accesses" which restricts behavior of arrays, vectors, structs, etc. We will want to include that language in KHR_robustness at least as GLSL-specific language; if ES wants to adopt the broader language for GLSL-ES that might still be doable. Revision History Rev. Date Author Changes ---- ------------ --------- ------------------------------------------ 11 2014/08/21 Jon Leech Fix typo. 10 2014/06/26 Jon Leech Change from OES to KHR. Update issues 1 and 9; add issue 12 on ES / GL differences. 9 2014/06/26 Jon Leech Minor phrasing fixes to be more consistent with equivalent GL functionality. 8 2014/06/24 Jon Leech Fix typos & mention GetError in issue 5. Reorder API spec edits in section order. Resolve issues 9-11 (Bug 12104 comments #42-45). Assign CONTEXT_LOST enum. 7 2014/06/02 Jon Leech Remove "safe" return value behavior for queries when contexts are lost (Bug 12104 comment #27). 6 2014/06/02 Jon Leech Rebase extension on OpenGL ES 3.1 specs and reflow paragraphs (no functionality changes are made in this version). 5 2014/05/16 Jon Leech Add CONTEXT_LOST error and exceptional behavior for potentially-blocking commands (Bug 8411). 4 2014/05/14 Jon Leech Add issue 11 on behavior of GL calls made after a context is lost. 3 2014/05/07 Jon Leech Add GetnUniformuivOES for ES 3.0. 2 2014/04/26 Jon Leech Updates based on Ken's comments in bug 12104 and to reference EGL 1.5. 1 2014/04/23 Jon Leech Branch from EXT_robustness version 3 and promote to OES suffixes. Add issues 9-10.