From 5bfde967dcbbfae884e343425da1fc069a9c4b86 Mon Sep 17 00:00:00 2001
From: Gabe Black <gabeblack@google.com>
Date: Fri, 16 Nov 2018 17:07:42 -0800
Subject: base: Set up a guard page for fiber stacks.

This will help detect stack overflow for fibers.

Change-Id: Iff2b102120ec351709e495291d6bead597f8d10c
Reviewed-on: https://gem5-review.googlesource.com/c/14395
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Gabe Black <gabeblack@google.com>
---
 src/base/fiber.cc | 39 ++++++++++++++++++++++++++++-----------
 src/base/fiber.hh |  4 +++-
 2 files changed, 31 insertions(+), 12 deletions(-)

diff --git a/src/base/fiber.cc b/src/base/fiber.cc
index eac1d9394..af63216da 100644
--- a/src/base/fiber.cc
+++ b/src/base/fiber.cc
@@ -33,7 +33,11 @@
 #include <valgrind/valgrind.h>
 #endif
 
+#include <sys/mman.h>
+#include <unistd.h>
+
 #include <cerrno>
+#include <cstdio>
 #include <cstring>
 
 #include "base/logging.hh"
@@ -71,28 +75,41 @@ Fiber::entryTrampoline()
     startingFiber->start();
 }
 
-Fiber::Fiber(size_t stack_size) :
-    link(primaryFiber()),
-    stack(stack_size ? new uint8_t[stack_size] : nullptr),
-    stackSize(stack_size), started(false), _finished(false)
+Fiber::Fiber(size_t stack_size) : Fiber(primaryFiber(), stack_size)
+{}
+
+Fiber::Fiber(Fiber *link, size_t stack_size) :
+    link(link), stack(nullptr), stackSize(stack_size), guardPage(nullptr),
+    guardPageSize(sysconf(_SC_PAGE_SIZE)), started(false), _finished(false)
 {
+    if (stack_size) {
+        guardPage = mmap(nullptr, guardPageSize + stack_size,
+                         PROT_READ | PROT_WRITE,
+                         MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
+        if (guardPage == (void *)MAP_FAILED) {
+            perror("mmap");
+            fatal("Could not mmap %d byte fiber stack.\n", stack_size);
+        }
+        stack = (void *)((uint8_t *)guardPage + guardPageSize);
+        if (mprotect(guardPage, guardPageSize, PROT_NONE)) {
+            perror("mprotect");
+            fatal("Could not forbid access to fiber stack guard page.");
+        }
+    }
 #if HAVE_VALGRIND
-    valgrindStackId = VALGRIND_STACK_REGISTER(stack, stack + stack_size);
+    valgrindStackId = VALGRIND_STACK_REGISTER(
+            stack, (uint8_t *)stack + stack_size);
 #endif
 }
 
-Fiber::Fiber(Fiber *link, size_t stack_size) :
-    link(link), stack(stack_size ? new uint8_t[stack_size] : nullptr),
-    stackSize(stack_size), started(false), _finished(false)
-{}
-
 Fiber::~Fiber()
 {
     panic_if(stack && _currentFiber == this, "Fiber stack is in use.");
 #if HAVE_VALGRIND
     VALGRIND_STACK_DEREGISTER(valgrindStackId);
 #endif
-    delete [] stack;
+    if (guardPage)
+        munmap(guardPage, guardPageSize + stackSize);
 }
 
 void
diff --git a/src/base/fiber.hh b/src/base/fiber.hh
index 3d82075f0..4d95e032b 100644
--- a/src/base/fiber.hh
+++ b/src/base/fiber.hh
@@ -106,8 +106,10 @@ class Fiber
     Fiber *link;
 
     // The stack for this context, or a nullptr if allocated elsewhere.
-    uint8_t *stack;
+    void *stack;
     size_t stackSize;
+    void *guardPage;
+    size_t guardPageSize;
 #if HAVE_VALGRIND
     unsigned valgrindStackId;
 #endif
-- 
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