Abstract: Several features pertain to processors equipped for speculative execution of processor code following a branch prediction. As described herein, asymmetric conditional branch instructions are provided for use by programmers and/or compilers to block speculation along one branch pathway while allowing speculation along another pathway. That is, a new type of branch instruction is described in which the encoding specifies that it is asymmetrically speculative (or asymmetrically nonspeculative). Techniques are also described for protecting sensitive information from certain types of malicious attacks, such as side-channel attacks, by employing asymmetrically speculative/nonspeculative conditional branching. For example, an asymmetric branch instruction may be used to block speculation along a vulnerable branch that exposes sensitive information to a side-channel attack, while nevertheless allowing speculation along another branch.

Abstract: In an aspect, an apparatus defines a group of registers that includes at least one of a plurality of registers in an integrated circuit. Each of the plurality of registers in the integrated circuit may be constrained to one of a plurality of fixed groups of registers. The apparatus applies a first set of access control rules to the group of registers, the first set of access control rules configured to override any of a second set of access control rules applied to the one or more fixed groups of registers.

Abstract: Several features pertain to computing systems equipped to perform speculative processing and configured to access device memory (e.g. non-speculative or unspeculatable memory) and non-device memory (e.g. speculative or speculatable memory). Malicious attacks may seek to obtain sensitive information from such systems by exploiting speculative code execution. Herein, techniques are described whereby sensitive data is protected from such attacks by placing the data in a page of memory not ordinarily used as device memory, and then designating or marking the page as device memory (e.g. marking the page as unspeculatable). By designating the page as unspeculatable device memory, the processor does not speculatively access the sensitive information (e.g. speculation stops once a branch is invoked that would access the page) and so certain types of attacks can be mitigated.