llvm-project

7dbfc2bd - [lldb][AArch64][Linux] Add support for the Permission Overlay Extension (POE) (#177145)

[lldb][AArch64][Linux] Add support for the Permission Overlay Extension (POE) (#177145) This change adds initial support for managing the Permission Overlay Extension (POE). This extension allows userspace programs to change memory permissions without making a sycall. This is used to implement Linux's memory protection keys (https://docs.kernel.org/core-api/protection-keys.html) on AArch64. Overview of POE: * Page table entries have a set of permissions. To change these, a program would have to use a syscall which adds overhead. * 3 bits of the page table entry are used for a protection key 0-7. * POE adds a new register "por" (POR_EL0 in the manual) which stores 4-bit sets of permissions. * The protection key is an index into this por register. * Permissions in POR are applied on top of the page table permissions, but may only remove permissions. For example, if you overlay read/execute over read/write, the result is read. Since execute was not in the page table permissions. * This register can be modified without leaving userspace, making permission changes faster. To help debug this, I have made the following changes to LLDB: * Ability to read and write the por register. * Save and restore of por when running expressions. * Register field definitions to print the por permissions in a human readable form. * Recognition of memory protection key faults as a distinct type of SIGSEGV (this will apply to Linux on any architecture). There are a few more features to add around memory region information, that will be in follow up changes. As will documentation and release notes for all the POE features.