When using Arm Cortex-M Security Extensions (CMSE), Secure stack contents can be leaked to Non-secure state via floating-point registers when a Secure to Non-secure function call is made that returns a floating-point value and when this is the first use of floating-point since entering Secure state. This allows an attacker to read a limited quantity of Secure stack contents with an impact on confidentiality. This issue is specific to code generated using LLVM-based compilers.
The product releases a resource such as memory or a file so that it can be made available for reuse, but it does not clear or “zeroize” the information contained in the resource before the product performs a critical state transition or makes the resource available for reuse by other entities.
When resources are released, they can be made available for reuse. For example, after memory is de-allocated, an operating system may make the memory available to another process, or disk space may be reallocated when a file is deleted. As removing information requires time and additional resources, operating systems do not usually clear the previously written information. Even when the resource is reused by the same process, this weakness can arise when new data is not as large as the old data, which leaves portions of the old data still available. Equivalent errors can occur in other situations where the length of data is variable but the associated data structure is not. If memory is not cleared after use, the information may be read by less trustworthy parties when the memory is reallocated. This weakness can apply in hardware, such as when a device or system switches between power, sleep, or debug states during normal operation, or when execution changes to different users or privilege levels.