From f7fcffc429b0271115d50f594a6ae7a83e888958 Mon Sep 17 00:00:00 2001
From: Matthew LeVan <matthew@coeli.network>
Date: Fri, 19 Jan 2024 16:46:09 -0500
Subject: [PATCH] wip: friday

---
 rust/ares_guard/build.rs      | 16 +++----
 rust/ares_guard/c-src/guard.c | 80 ++++++++++++++++++++---------------
 2 files changed, 53 insertions(+), 43 deletions(-)

diff --git a/rust/ares_guard/build.rs b/rust/ares_guard/build.rs
index a67919d..8205747 100644
--- a/rust/ares_guard/build.rs
+++ b/rust/ares_guard/build.rs
@@ -37,17 +37,17 @@ fn main() {
         .flag("-g3")
         .flag("-Wall")
         .flag("-Wextra")
-        .flag("-Wgnu-pointer-arith")
-        .flag("-Wpointer-arith")
-        .flag("-Wpedantic")
         .flag("-Wformat=2")
-        .flag("-Wno-unused-parameter")
+        .flag("-Wmissing-include-dirs")
+        .flag("-Wnested-externs")
+        .flag("-Wold-style-definition")
+        .flag("-Wpedantic")
+        .flag("-Wredundant-decls")
         .flag("-Wshadow")
         .flag("-Wwrite-strings")
-        .flag("-Wold-style-definition")
-        .flag("-Wredundant-decls")
-        .flag("-Wnested-externs")
-        .flag("-Wmissing-include-dirs")
+        .flag("-Wno-unused-parameter")
+        .flag("-Wno-pointer-arith")
+        .flag("-Wno-strict-prototypes")
         .try_compile("guard");
 
     if let Err(err) = res {
diff --git a/rust/ares_guard/c-src/guard.c b/rust/ares_guard/c-src/guard.c
index 508f207..6e77b14 100644
--- a/rust/ares_guard/c-src/guard.c
+++ b/rust/ares_guard/c-src/guard.c
@@ -7,7 +7,8 @@
 #include "guard.h"
 
 
-#define GD_PAGESZ 16384
+#define GD_PAGEBITS 14ULL
+#define GD_PAGESIZE (1ULL << GD_PAGEBITS) /* 16K */
 
 static void *guard_p = NULL;
 static void *stack_p = NULL;
@@ -19,45 +20,60 @@ typedef enum {
   guard_weird = 2, // strange state
   guard_spent = 3, // out of memory (bail:meme)
   guard_erupt = 4, // sigint
-} guard_err_t;
+} guard_error;
 
 volatile sig_atomic_t guard_err = guard_sound;
 
 
-guard_err_t _focus_guard(void *si_addr) {
+// Center the guard page.
+guard_error _focus_guard() {
   // Check for strange situations.
-  if (stack_p == NULL || alloc_p == NULL || si_addr == NULL) {
+  if (stack_p == NULL || alloc_p == NULL) {
     return guard_weird;
   }
 
-  // Re-center the guard page if the fault address falls within it.
-  if (si_addr >= guard_p && si_addr < guard_p + GD_PAGESZ) {
-    // Unmark the old guard page.
-    void *old_guard_pg = guard_p;
-    if (mprotect(old_guard_pg, GD_PAGESZ, PROT_READ | PROT_WRITE) == -1) {
+  // Unmark the old guard page.
+  void *old_guard_p = guard_p;
+  if (mprotect(old_guard_p, GD_PAGESIZE, PROT_READ | PROT_WRITE) == -1) {
+    return guard_armor;
+  }
+
+  // Place the new guard page in the center.
+  if (stack_p > alloc_p) {
+    guard_p = stack_p - ((stack_p - alloc_p) / 2);
+  }
+  else if (stack_p < alloc_p) {
+    guard_p = stack_p + ((alloc_p - stack_p) / 2);
+  }
+  else {
+    return guard_weird;
+  }
+  guard_p = (void *)((uintptr_t)guard_p & ~(GD_PAGESIZE - 1));
+
+  // Mark the new guard page.
+  if (guard_p != old_guard_p) {
+    if (mprotect(guard_p, GD_PAGESIZE, PROT_NONE) == -1) {
       return guard_armor;
     }
-
-    // Place the new guard page in the center.
-    guard_p = stack_p + ((alloc_p - stack_p) / 2);
-    // TODO: Ensure the guard_p is page-aligned.
-    // guard_p = (void *)((uintptr_t)guard_p & ~(GD_PAGESZ - 1));
-    if (guard_p != old_guard_pg) {
-      if (mprotect(guard_p, GD_PAGESZ, PROT_NONE) == -1) {
-        return guard_armor;
-      }
-    } else {
-      return guard_spent;
-    }
+  } else {
+    return guard_spent;
   }
 
   return guard_sound;
 }
 
+guard_error _slash_guard(void *si_addr) {
+  if (si_addr >= guard_p && si_addr < guard_p + GD_PAGESIZE) {
+    return _focus_guard();
+  }
+
+  return guard_weird;
+}
+
 void _signal_handler(int sig, siginfo_t *si, void *unused) {
   switch (sig) {
     case SIGSEGV:
-      guard_err = _focus_guard(si->si_addr);
+      guard_err = _slash_guard(si->si_addr);
       break;
     case SIGINT:
       guard_err = guard_erupt;
@@ -67,37 +83,31 @@ void _signal_handler(int sig, siginfo_t *si, void *unused) {
   }
 }
 
-guard_err_t _register_handler() {
-  guard_err_t err = guard_sound;
+guard_error _register_handler() {
   struct sigaction sa;
 
   sa.sa_flags = SA_SIGINFO;
   sa.sa_sigaction = _signal_handler;
   sa.sa_mask = 0;
 
-  if (sigaction(SIGSEGV, &sa, NULL)) {
-    err = guard_weird;
+  if (sigaction(SIGSEGV, &sa, NULL) || sigaction(SIGINT, &sa, NULL)) {
+    return guard_weird;
   }
 
-  return guard_err;
+  return guard_sound;
 }
 
 void guard(void *(*f)(void *), void *arg, void **stack, void **alloc, void **ret) {
-  guard_err_t err;
   stack_p = *stack;
   alloc_p = *alloc;
 
   if (_register_handler() != guard_sound) {
-    err = guard_weird;
+    guard_err = guard_weird;
     goto fail;
   }
 
-  if (guard_p == NULL) {
-    guard_p = stack_p + ((alloc_p - stack_p) / 2);
-    if (mprotect(guard_p, GD_PAGESZ, PROT_NONE) == -1) {
-      err = guard_armor;
-      goto fail;
-    }
+  if (guard_p == NULL && (guard_err = _focus_guard()) != guard_sound) {
+    goto fail;
   }
 
   *ret = f(arg);