[libunwind] Support new frame layout of rtld-c18n #732
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This commit adds support for backtrace and exception handling in libunwind when the process is running with the compartmentalization runtime linker. The unwinding process remains the same until a trampoline is encountered as the return address. This means that we are crossing compartment boundaries and we need to gather the unwind information from the runtime linker. We do this by reading information from the executive stack that the runtime linker populates for us in unw_getcontext. It also adds a new class, CompartmentInfo, which is responsible for abstracting away the details of c18n compartments. Currently, it is only used to define the constants relating to the trusted frame layout. There are two ways to compile this code: - LIBUNWIND_SANDBOX_OTYPES only; - LIBUNWIND_SANDBOX_OTYPES and LIBUNWIND_SANDBOX_HARDENED. When LIBUNWIND_SANDBOX_HARDENED is specified, every stack pointer, frame pointer and callee-saved register will be sealed in the unwind register context. This is to prevent leakage of capabilities through the register context as much as possible. There are two exceptions to this: - When unw_set_reg() is called from a libunwind consumer, the caller might expect to be able to retrieve the capability it stored in the context, and sealing it will break the API semantics; - When the capability that is in the context is a sentry. These can't be sealed using an otype. The otype allocated to libunwind is given to libunwind by the runtime linker via the _rtld_unw_getsealer function. This functionality only works on Morello right now.
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This is now merged and squashed into a clean history |
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This updates the unwinder to support the changes in CTSRD-CHERI/cheribsd#2079.