[compiler-rt] [sanitizer] Add re-execution on FreeBSD when ASLR is detected (PR #73439)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Dimitry Andric (DimitryAndric)

<details>
<summary>Changes</summary>

In the FreeBSD base system, re-executing the main binary when ASLR is detected was implemented in the following commits:

* freebsd/freebsd-src@<!-- -->7cafe89f9ce33
* freebsd/freebsd-src@<!-- -->96fe7c8ab0f65
* freebsd/freebsd-src@<!-- -->930a7c2ac67e1
* freebsd/freebsd-src@<!-- -->0a736f0a6aeb0
* freebsd/freebsd-src@<!-- -->4c9a0adad1826

Squash all these to bring them into upstream compiler-rt.

When ASLR is detected to be enabled, this first force-disables ASLR for the current process, then calls ReExec(). The ReExec() function gets a FreeBSD specific implementation for finding the path of the executed program, via the ELF auxiliary vector. This is done without calling into the regular elf_aux_info(3) function, as that makes use of several already-intercepted functions.

---
Full diff: https://github.com/llvm/llvm-project/pull/73439.diff


2 Files Affected:

- (modified) compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp (+6-3) 
- (modified) compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp (+11-1) 


``````````diff
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp
index d2b3b63f3a7a3bd..8759d96609e567c 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux.cpp
@@ -2323,9 +2323,12 @@ void CheckASLR() {
     return;
   }
   if ((aslr_status & PROC_ASLR_ACTIVE) != 0) {
-    Printf("This sanitizer is not compatible with enabled ASLR "
-           "and binaries compiled with PIE\n");
-    Die();
+    VReport(1, "This sanitizer is not compatible with enabled ASLR "
+               "and binaries compiled with PIE\n"
+               "ASLR will be disabled and the program re-executed.\n");
+    int aslr_ctl = PROC_ASLR_FORCE_DISABLE;
+    CHECK_NE(internal_procctl(P_PID, 0, PROC_ASLR_CTL, &aslr_ctl), -1);
+    ReExec();
   }
 #  elif SANITIZER_PPC64V2
   // Disable ASLR for Linux PPC64LE.
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
index fcfaa0c36c2251b..ea816eacd980249 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
@@ -47,13 +47,16 @@
 
 #if SANITIZER_FREEBSD
 #include <pthread_np.h>
+#include <stdlib.h>
 #include <osreldate.h>
+#include <sys/auxv.h>
 #include <sys/sysctl.h>
 #define pthread_getattr_np pthread_attr_get_np
 // The MAP_NORESERVE define has been removed in FreeBSD 11.x, and even before
 // that, it was never implemented. So just define it to zero.
 #undef MAP_NORESERVE
 #define MAP_NORESERVE 0
+extern const Elf_Auxinfo *__elf_aux_vector;
 #endif
 
 #if SANITIZER_NETBSD
@@ -941,7 +944,14 @@ u64 MonotonicNanoTime() {
 void ReExec() {
   const char *pathname = "/proc/self/exe";
 
-#if SANITIZER_NETBSD
+#if SANITIZER_FREEBSD
+  for (const auto *aux = __elf_aux_vector; aux->a_type != AT_NULL; aux++) {
+    if (aux->a_type == AT_EXECPATH) {
+      pathname = static_cast<const char *>(aux->a_un.a_ptr);
+      break;
+    }
+  }
+#elif SANITIZER_NETBSD
   static const int name[] = {
       CTL_KERN,
       KERN_PROC_ARGS,

``````````

</details>


https://github.com/llvm/llvm-project/pull/73439