[msan] Check qsort input.

Summary:
Qsort interceptor suppresses all checks by unpoisoning the data in the
wrapper of a comparator function, and then unpoisoning the output array
as well.

This change adds an explicit run of the comparator on all elements of
the input array to catch any sanitizer bugs.

Reviewers: vitalybuka

Subscribers: #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D71780

Author: eugenis

compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc

@@ -9665,6 +9665,15 @@ INTERCEPTOR(void, qsort, void *base, SIZE_T nmemb, SIZE_T size,
             qsort_compar_f compar) {
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, qsort, base, nmemb, size, compar);
+  // Run the comparator over all array elements to detect any memory issues.
+  for (SIZE_T i = 0; i < nmemb; ++i) {
+    void *p = (void *)((char *)base + i * size);
+    COMMON_INTERCEPTOR_UNPOISON_PARAM(2);
+    // Compare each element with itself to trigger an equality check, which
+    // typically requires the comparator to look as many of the object fields as
+    // possible.
+    compar(p, p);
+  }
   qsort_compar_f old_compar = qsort_compar;
   qsort_compar = compar;
   SIZE_T old_size = qsort_size;
@@ -9694,6 +9703,15 @@ INTERCEPTOR(void, qsort_r, void *base, SIZE_T nmemb, SIZE_T size,
             qsort_r_compar_f compar, void *arg) {
   void *ctx;
   COMMON_INTERCEPTOR_ENTER(ctx, qsort_r, base, nmemb, size, compar, arg);
+  // Run the comparator over all array elements to detect any memory issues.
+  for (SIZE_T i = 0; i < nmemb; ++i) {
+    void *p = (void *)((char *)base + i * size);
+    COMMON_INTERCEPTOR_UNPOISON_PARAM(3);
+    // Compare each element with itself to trigger an equality check, which
+    // typically requires the comparator to look as many of the object fields as
+    // possible.
+    compar(p, p, arg);
+  }
   qsort_r_compar_f old_compar = qsort_r_compar;
   qsort_r_compar = compar;
   SIZE_T old_size = qsort_r_size;

compiler-rt/test/msan/qsort.cpp

@@ -1,4 +1,5 @@
 // RUN: %clangxx_msan -O0 -g %s -o %t && %run %t
+// RUN: %clangxx_msan -DPOISON -O0 -g %s -o %t && not %run %t 2>&1 | FileCheck %s
 
 #include <assert.h>
 #include <errno.h>
@@ -65,6 +66,10 @@ int main(int argc, char *argv[]) {
   for (int i = 0; i < kSize1; ++i)
     p[i] = i * 2 + (i % 3 - 1) * 3;
   poison_stack_and_param();
+#ifdef POISON
+  __msan_poison(p + 1, sizeof(long));
+  // CHECK: Uninitialized bytes in __msan_check_mem_is_initialized at offset 0 inside [{{.*}}, 8)
+#endif
   qsort(p, kSize1, sizeof(long), compar1);
   __msan_check_mem_is_initialized(p, sizeof(long) * kSize1);
   assert(seen2);