[llvm] r358478 - Asan use-after-scope: don't poison allocas if there were untraced lifetime intrinsics in the function (PR41481)

[Hans Wennborg via llvm-commits]

Author: hans
Date: Tue Apr 16 00:54:20 2019
New Revision: 358478

URL: http://llvm.org/viewvc/llvm-project?rev=358478&view=rev
Log:
Asan use-after-scope: don't poison allocas if there were untraced lifetime intrinsics in the function (PR41481)

If there are any intrinsics that cannot be traced back to an alloca, we
might have missed the start of a variable's scope, leading to false
error reports if the variable is poisoned at function entry. Instead, if
there are some intrinsics that can't be traced, fail safe and don't
poison the variables in that function.

Differential revision: https://reviews.llvm.org/D60686

Modified:
    llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
    llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-and-lifetime.ll

Modified: llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp?rev=358478&r1=358477&r2=358478&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Instrumentation/AddressSanitizer.cpp Tue Apr 16 00:54:20 2019
@@ -884,6 +884,7 @@ struct FunctionStackPoisoner : public In
   };
   SmallVector<AllocaPoisonCall, 8> DynamicAllocaPoisonCallVec;
   SmallVector<AllocaPoisonCall, 8> StaticAllocaPoisonCallVec;
+  bool HasUntracedLifetimeIntrinsic = false;
 
   SmallVector<AllocaInst *, 1> DynamicAllocaVec;
   SmallVector<IntrinsicInst *, 1> StackRestoreVec;
@@ -918,6 +919,14 @@ struct FunctionStackPoisoner : public In
 
     initializeCallbacks(*F.getParent());
 
+    if (HasUntracedLifetimeIntrinsic) {
+      // If there are lifetime intrinsics which couldn't be traced back to an
+      // alloca, we may not know exactly when a variable enters scope, and
+      // therefore should "fail safe" by not poisoning them.
+      StaticAllocaPoisonCallVec.clear();
+      DynamicAllocaPoisonCallVec.clear();
+    }
+
     processDynamicAllocas();
     processStaticAllocas();
 
@@ -1040,8 +1049,12 @@ struct FunctionStackPoisoner : public In
     // Find alloca instruction that corresponds to llvm.lifetime argument.
     AllocaInst *AI =
         llvm::findAllocaForValue(II.getArgOperand(1), AllocaForValue);
+    if (!AI) {
+      HasUntracedLifetimeIntrinsic = true;
+      return;
+    }
     // We're interested only in allocas we can handle.
-    if (!AI || !ASan.isInterestingAlloca(*AI))
+    if (!ASan.isInterestingAlloca(*AI))
       return;
     bool DoPoison = (ID == Intrinsic::lifetime_end);
     AllocaPoisonCall APC = {&II, AI, SizeValue, DoPoison};

Modified: llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-and-lifetime.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-and-lifetime.ll?rev=358478&r1=358477&r2=358478&view=diff
==============================================================================
--- llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-and-lifetime.ll (original)
+++ llvm/trunk/test/Instrumentation/AddressSanitizer/stack-poisoning-and-lifetime.ll Tue Apr 16 00:54:20 2019
@@ -209,6 +209,42 @@ entry:
   ; CHECK: ret void
 }
 
+declare void @foo(i32*)
+define void @PR41481(i1 %b) sanitize_address {
+; CHECK-LABEL: @PR41481
+entry:
+  %p1 = alloca i32
+  %p2 = alloca i32
+  %q1 = bitcast i32* %p1 to i8*
+  %q2 = bitcast i32* %p2 to i8*
+  br label %bb1
+
+  ; Since we cannot account for all lifetime intrinsics in this function, we
+  ; might have missed a lifetime.start one and therefore shouldn't poison the
+  ; allocas at function entry.
+  ; ENTRY: store i64 -935356719533264399
+  ; ENTRY-UAS: store i64 -935356719533264399
+
+bb1:
+  %p = select i1 %b, i32* %p1, i32* %p2
+  %q = select i1 %b, i8*  %q1, i8*  %q2
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* %q)
+  call void @foo(i32* %p)
+  br i1 %b, label %bb2, label %bb3
+
+bb2:
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %q1)
+  br label %end
+
+bb3:
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* %q2)
+  br label %end
+
+end:
+  ret void
+}
+
+
 declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
 declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)