hs_pow: Add CompiledProofOfWorkHash torrc option

This exposes the new fallback behavior in hashx via a new AUTOBOOL
configuration option, available to both clients and services. The
default should be fine for nearly everyone, but it might be necessary
to enable or disable the compiler manually for diagnostic purposes.

Signed-off-by: Micah Elizabeth Scott <beth@torproject.org>

3 files changed, 26 insertions, 5 deletions

diff --git a/src/feature/hs/hs_client.c b/src/feature/hs/hs_client.c
index 0e4b3ca0c3..2bb59f078e 100644
--- a/src/feature/hs/hs_client.c
+++ b/src/feature/hs/hs_client.c
@@ -750,7 +750,8 @@ consider_sending_introduce1(origin_circuit_t *intro_circ,
    */
   if (have_module_pow() && desc->encrypted_data.pow_params) {
     hs_pow_solver_inputs_t pow_inputs = {
-      .effort = desc->encrypted_data.pow_params->suggested_effort
+      .effort = desc->encrypted_data.pow_params->suggested_effort,
+      .CompiledProofOfWorkHash = get_options()->CompiledProofOfWorkHash
     };
     ed25519_pubkey_copy(&pow_inputs.service_blinded_id,
                         &desc->plaintext_data.blinded_pubkey);
diff --git a/src/feature/hs/hs_pow.c b/src/feature/hs/hs_pow.c
index 27d09cb0b4..5cee3b00d7 100644
--- a/src/feature/hs/hs_pow.c
+++ b/src/feature/hs/hs_pow.c
@@ -175,9 +175,24 @@ unpack_equix_solution(const uint8_t *bytes_in,
   }
 }
 
+/** Helper: Map the CompiledProofOfWorkHash configuration option to its
+ * corresponding equix_ctx_flags bit. */
+static equix_ctx_flags
+hs_pow_equix_option_flags(int CompiledProofOfWorkHash)
+{
+  if (CompiledProofOfWorkHash == 0) {
+    return 0;
+  } else if (CompiledProofOfWorkHash == 1) {
+    return EQUIX_CTX_MUST_COMPILE;
+  } else {
+    tor_assert_nonfatal(CompiledProofOfWorkHash == -1);
+    return EQUIX_CTX_TRY_COMPILE;
+  }
+}
+
 /** Solve the EquiX/blake2b PoW scheme using the parameters in pow_params, and
  * store the solution in pow_solution_out. Returns 0 on success and -1
- * otherwise. Called by a client. */
+ * otherwise. Called by a client, from a cpuworker thread. */
 int
 hs_pow_solve(const hs_pow_solver_inputs_t *pow_inputs,
              hs_pow_solution_t *pow_solution_out)
@@ -198,7 +213,10 @@ hs_pow_solve(const hs_pow_solver_inputs_t *pow_inputs,
   challenge = build_equix_challenge(&pow_inputs->service_blinded_id,
                                     pow_inputs->seed, nonce, effort);
 
-  ctx = equix_alloc(EQUIX_CTX_SOLVE | EQUIX_CTX_TRY_COMPILE);
+  /* This runs on a cpuworker, let's not access global get_options().
+   * Instead, the particular options we need are captured in pow_inputs. */
+  ctx = equix_alloc(EQUIX_CTX_SOLVE |
+    hs_pow_equix_option_flags(pow_inputs->CompiledProofOfWorkHash));
   if (!ctx) {
     goto end;
   }
@@ -339,7 +357,8 @@ hs_pow_verify(const ed25519_public_key_t *service_blinded_id,
     goto done;
   }
 
-  ctx = equix_alloc(EQUIX_CTX_VERIFY | EQUIX_CTX_TRY_COMPILE);
+  ctx = equix_alloc(EQUIX_CTX_VERIFY |
+    hs_pow_equix_option_flags(get_options()->CompiledProofOfWorkHash));
   if (!ctx) {
     goto done;
   }
@@ -428,7 +447,6 @@ pow_worker_threadfn(void *state_, void *work_)
   job->pow_solution_out = tor_malloc_zero(sizeof(hs_pow_solution_t));
 
   if (hs_pow_solve(&job->pow_inputs, job->pow_solution_out)) {
-    log_warn(LD_REND, "Failed to run the proof of work solver");
     tor_free(job->pow_solution_out);
     job->pow_solution_out = NULL; /* how we signal that we came up empty */
   }
diff --git a/src/feature/hs/hs_pow.h b/src/feature/hs/hs_pow.h
index b5949b7916..d47eba82ab 100644
--- a/src/feature/hs/hs_pow.h
+++ b/src/feature/hs/hs_pow.h
@@ -84,6 +84,8 @@ typedef struct hs_pow_solver_inputs_t {
   /** Effort chosen by the client. May be higher or lower than
    * suggested_effort in the descriptor. */
   uint32_t effort;
+  /** Configuration option, choice of hash implementation. AUTOBOOL. */
+  int CompiledProofOfWorkHash;
 } hs_pow_solver_inputs_t;
 
 /** State and parameters of PoW defenses, stored in the service state. */