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This directory contains the Coq mechanization accompanying the submission "Efficient and Provable Local Capability Revocation using Uninitialized Capabilities".

Building and browsing the proofs

You need to have opam >= 2.0 installed. If this is the first time you install opam, you additionally need to run opam init.

Then, let us create a fresh local opam switch with everything needed. This will install coq and iris in a local _opam directory:

   opam switch create -y --repositories=default,coq-released=https://coq.inria.fr/opam/released . ocaml-base-compiler.4.08.1
   eval $(opam env)
   opam install coqide  # optional, but useful to browse the proofs

Then, build the development:

make -jN  # replace N with the number of CPU cores of your machine

We recommend that you have 32Gb of RAM+swap. Please be aware that the development takes around 1h to compile. In particular, the files theories/examples/awkward_example{,_u}.v can each take up to 25 minutes to compile.

It is possible to run make fundamental to only build files up to the Fundamental Theorem. This usually takes up 20 minutes.

After building, one can use coqide to browse the proofs (ProofGeneral works as well):

coqide theories/fundamental.v  # for instance

Troubleshooting

If the opam invocation fails at some point, either remove the _opam directory and re-run the command (this will redo everything), or do eval $(opam env) and then opam install -y . (this will continue from where it failed).

Cleanup

It is enough to remove the _opam directory to get rid of everything that has been installed for building the proofs.

To additionally get rid of anything opam-related in general, additionally remove ~/.opam (if you just installed opam and do not plan on using it further).

Documentation

After building the development, documentation generated using Coqdoc can be created using make html.

Then, browse the html/toc.html file.

Note that we have included a copy of the generated html files as a supplemental material.

Organization

First is a lookup table for the definitions in the paper.

paper file or folder name
Machine words, machine state and instructions (Fig 1) machine_base.v
Permission and locality hierarchy (Fig 2) machine_base.v PermFlowsTo - LocalityFlowsTo
Operational semantics: reduction steps (Fig 3) cap_lang.v prim_step
Operational semantics: instruction semantics (Fig 4) cap_lang.v exec
Separation Logic Specifications (Fig 6) rules/* e.g. rules_Store.v\wp_store_success_reg
rclear Specification (Fig 6) examples/stack_macros.v rclear_spec
Safety with Revocation (Fig 9) logrel.v
Expression relation (Fig 9) logrel.v interp_expr
Register relation (Fig 9) logrel.v interp_reg
Value relation (Fig 9) logrel.v interp1 (and its fixpoint interp)
State relation (Fig 9) logrel.v region_state_*
Standard State Transition System (Fig 10) region_invariants.v region_type with std_rel_pub and std_rel_priv
Standard Resources (Fig 11) region_invariants.v inlined in region_map_def
Mstd sts.v sts_full_std, with the global gname (γs_std)
Mcus sts.v sts_full, with the global gnames (γs_loc,γr_loc)
stsCollection sts.v sts_full_world
sharedResources region_invariants.v region
Fundamental Theorem of Logical Relations (Theorem 6.1) fundamental.v fundamental_from_interp
Awkward Example: g1 (Fig 13) examples/awkward_example_preamble.v awkward_preamble_instrs
Awkward Example: f1 (Fig 13) examples/awkward_example_u.v awkward_instrs
Lemma 6.2 examples/awkward_example_preamble.v awkward_preamble_spec
Theorem 6.3 examples/awkward_example_adequacy.v awkward_example_adequacy

Next we describe the file organization of the implementation.

The organization of the theories/ folder is as follows.

Operational semantics

  • addr_reg.v: Defines registers and the set of (finite) memory addresses.

  • machine_base.v: Contains the syntax (permissions, capability, instructions, ...) of the capability machine.

  • machine_parameters.v: Defines a number of "settings" for the machine, that parameterize the whole development (e.g. the specific encoding scheme for instructions, etc.).

  • cap_lang.v: Defines the operational semantics of the machine, and the embedding of the capability machine language into Iris.

  • machine_run.v: Defines an executable version of the operational semantics, allowing to use them as an interpreter to run a concrete machine configuration.

Program logic

  • monocmra.v, mono_ref.v: Definition of monotonic references in Iris, used to define the points-to predicate for memory addresses.

  • region.v: Auxiliary definitions to reason about consecutive range of addresses and memory words.

  • rules_base.v: Contains some of the core resource algebras for the program logic, namely the definition for points to predicates with permissions.

  • rules.v: Imports all the Hoare triple rules for each instruction. These rules are separated into separate files (located in the rules/ folder).

Logical relation

  • multiple_updates.v: Auxiliary definitions to reason about multiple updates to a world.

  • region_invariants.v: Definitions for standard resources, and the shared resources map sharedResources. Contains some lemmas for "opening" and "closing" the map, akin to opening and closing invariants.

  • region_invariants_revocation.v: Lemmas for revoking standard resources (setting Temporary invariants to a Revoked state).

  • region_invariants_static.v: Lemmas for manipulating frozen standard resources.

  • region_invariants_uninitialized.v: Lemmas for manipulating frozen standard singleton resources. These are specifically for manipulating the resources that are related to the interpretation of uninitialized capabilities.

  • sts.v: The definition of stsCollection, and associated lemmas.

  • logrel.v: The definition of the logical relation.

  • monotone.v: Proof of the monotonicity of the value relation with regards to public future worlds, and private future worlds for non local words.

  • fundamental.v: Contains Theorem 6.1: fundamental theorem of logical relations. Each case (one for each instruction) is proved in a separate file (located in the ftlr/ folder), which are all imported and applied in this file.

Case studies

In the examples folder:

  • stack_macros.v and stack_macros_u.v: Specifications for some useful macros, the former for a RWLX stack and the latter for a URWLX stack.

  • scall.v, scall_u.v: Specification of a safe calling convention for a RWLX and URWLX stack respectively. Each specification is split up into two parts: the prologue is the specification for the code before the jump, the epilogue is the specification for the activation record.

  • lse.v : A small and simple example that relies on local state encapsulation.

  • malloc.v: A simple malloc implementation, and its specification.

  • awkward_example.v, awkward_example_u.v: The proof of safety for the body of the awkward example (the former using scall with stack clearing, the latter using scallU without stack clearing).

  • awkward_example_preamble.v: Proof of safety of the preamble to the awkward example (in which a closure to the body of the awkward example is dynamically allocated). This corresponds to Lemma 6.2.

  • awkward_example_adequacy.v: Proof of correctness of the awkward example against the operational semantics of the machine, Theorem 6.3.

  • awkward_example_concrete.v: A concrete instantiation of the correctness theorem of the awkward example on a concrete machine, linked with a concrete "adversarial program". Then, we also prove that this concrete machine configurations indeed runs and gracefully halts.

Differences with the paper

Some definitions have different names from the paper.

name in paper => name in mechanization

In the operational semantics:

name in paper name in mechanization
SingleStep Instr Executable
Done Standby Instr NextI
Done Halted Instr Halted
Done Failed Instr Failed
Repeat _ Seq _

In the model:

name in paper name in mechanization
Frozen Static
stsCollection full_sts_world
sharedResources region

In scall.v and scall_u.v : the scall macro is in both cases slightly unfolded, as it does not include the part of the calling convention which stores local state on the stack. That part is inlined into the awkward examples.

In awkward_example_u.v: in the mechanized version of the awkward example (uninitialized version), we clear the local stack frame in two stages: before the second call, we clear the part of the frame which is frozen during the first call, but passed to the adversary during the second call (i.e. a single address at the top of the first local stack frame), and before returning to the caller we clear the rest of the local stack frame (see Section 4.2 for further detail on clearing the local stack frame upon returning to an adversary call).

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Formalisation of stack safety properties on a capability machine with local and uninitialized capabilities

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