1886563 - [meta] Make the location of immediate constants uncertain

Status: NEW

(Core :: JavaScript Engine: JIT, task, P3)

Description

[Nicolas B. Pierron [:nbp]]

Immediate constants are unavoidable, and moving all of them in a data-section might also be undesirable for performance and security reasons.

Also, register allocations and instruction opcodes might be a source of entropy that we would have to mitigate and that cannot easily be moved out of the code-section.

Thus we should add a MacroAssembler wrapping mechanism capable of relocating a section of code during the link-phase of the compilation.
The intent if to have a fixed-size assembly code generation where the linker will alternate between locations where the code might be relocated. The non-allocated location should be forged to cause a catastrophic failure of the program.

Thus, even if the generated content is known, the location would be uncertain, making JIT Spraying unreliable without reading the executable content.