[hwasan] Fix rare false negative (zero tag) in two more test cases (#69491)

stack-uas.c and stack-history-length.c both have
-hwasan-record-stack-history=libcall, which makes the stack base
tag fully randomized. They may therefore sometimes have a zero tag
for a stack allocated variable, resulting in a false negative

(#69221 (comment)).

This patch applies the same workaround as used for deep-recursion.c

(aa4dfd3)
and stack-uar.c

(ddf1de2):
have two adjacent stack-allocated variables, and use whichever is not
zero-tagged.

These are the last remaining test cases that use
-hwasan-record-stack-history=libcall.

stack-uas flakiness spotted in the wild:
https://lab.llvm.org/buildbot/#/builders/269/builds/549/steps/11/logs/stdio
stack-history-length:
https://lab.llvm.org/buildbot/#/builders/269/builds/537

Co-authored-by: Thurston Dang <[email protected]>

Author: thurstond

compiler-rt/test/hwasan/TestCases/stack-history-length.c

@@ -11,6 +11,8 @@
 // Stack histories are currently not recorded on x86.
 // XFAIL: target=x86_64{{.*}}
 
+#include <assert.h>
+#include <sanitizer/hwasan_interface.h>
 #include <stdlib.h>
 
 void USE(void *x) { // pretend_to_do_something(void *x)
@@ -20,7 +22,24 @@ void USE(void *x) { // pretend_to_do_something(void *x)
 volatile int four = 4;
 __attribute__((noinline)) void FUNC0() { int x[4]; USE(&x[0]); }
 __attribute__((noinline)) void FUNC() { int x[4]; USE(&x[0]); }
-__attribute__((noinline)) void OOB() { int x[4]; x[four] = 0; USE(&x[0]); }
+__attribute__((noinline)) void OOB() {
+  int x[4];
+  int y[4];
+  // With -hwasan-generate-tags-with-calls=false, stack tags can occasionally
+  // be zero, leading to a false negative
+  // (https://github.com/llvm/llvm-project/issues/69221). Work around it by
+  // using the neighboring variable, which is guaranteed by
+  // -hwasan-generate-tags-with-calls=false to have a different (hence
+  // non-zero) tag.
+  if (__hwasan_tag_pointer(x, 0) == x) {
+    assert(__hwasan_tag_pointer(y, 0) != y);
+    y[four] = 0;
+  } else {
+    x[four] = 0;
+  }
+  USE(&x[0]);
+  USE(&y[0]);
+}
 
 int main(int argc, char **argv) {
   int X = argc == 2 ? atoi(argv[1]) : 10;

compiler-rt/test/hwasan/TestCases/stack-uas.c

@@ -13,6 +13,10 @@
 // Stack histories currently are not recorded on x86.
 // XFAIL: target=x86_64{{.*}}
 
+#include <assert.h>
+#include <sanitizer/hwasan_interface.h>
+#include <stdio.h>
+
 void USE(void *x) { // pretend_to_do_something(void *x)
   __asm__ __volatile__(""
                        :
@@ -36,8 +40,20 @@ __attribute__((noinline)) void Unrelated3() {
 __attribute__((noinline)) char buggy() {
   char *volatile p;
   {
-    char zzz[0x1000] = {};
-    p = zzz;
+    char zzz[0x800] = {};
+    char yyy[0x800] = {};
+    // With -hwasan-generate-tags-with-calls=false, stack tags can occasionally
+    // be zero, leading to a false negative
+    // (https://github.com/llvm/llvm-project/issues/69221). Work around it by
+    // using the neighboring variable, which is guaranteed by
+    // -hwasan-generate-tags-with-calls=false to have a different (hence
+    // non-zero) tag.
+    if (__hwasan_tag_pointer(zzz, 0) == zzz) {
+      assert(__hwasan_tag_pointer(yyy, 0) != yyy);
+      p = yyy;
+    } else {
+      p = zzz;
+    }
   }
   return *p;
 }
@@ -53,7 +69,7 @@ int main() {
   // CHECK: Cause: stack tag-mismatch
   // CHECK: is located in stack of thread
   // CHECK: Potentially referenced stack objects:
-  // CHECK-NEXT: zzz in buggy {{.*}}stack-uas.c:[[@LINE-17]]
+  // CHECK-NEXT: {{zzz|yyy}} in buggy {{.*}}stack-uas.c:
   // CHECK-NEXT: Memory tags around the buggy address
 
   // NOSYM: Previously allocated frames: