[PATCH] D51334: SafeStack: Prevent OOB reads with mem intrinsics

[Vlad Tsyrklevich via Phabricator via llvm-commits]

vlad.tsyrklevich created this revision.
vlad.tsyrklevich added a reviewer: eugenis.
Herald added a subscriber: llvm-commits.

Currently, the SafeStack analysis disallows out-of-bounds writes but not
out-of-bounds reads for mem intrinsics like llvm.memcpy. This could
cause leaks of pointers to the safe stack by leaking spilled registers/
frame pointers. Check for allocas used as source or destination pointers
to mem intrinsics.


Repository:
  rL LLVM

https://reviews.llvm.org/D51334

Files:
  lib/CodeGen/SafeStack.cpp
  test/Transforms/SafeStack/X86/memintrinsic-oob-read.ll


Index: test/Transforms/SafeStack/X86/memintrinsic-oob-read.ll
===================================================================
--- /dev/null
+++ test/Transforms/SafeStack/X86/memintrinsic-oob-read.ll
@@ -0,0 +1,14 @@
+; RUN: opt -safe-stack -S -mtriple=i386-pc-linux-gnu < %s -o - | FileCheck %s
+; RUN: opt -safe-stack -S -mtriple=x86_64-pc-linux-gnu < %s -o - | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture writeonly, i8* nocapture readonly, i64, i1)
+
+; CHECK: __safestack_unsafe_stack_ptr
+define void @oob_read(i8* %ptr) safestack {
+  %1 = alloca i8
+  call void @llvm.memcpy.p0i8.p0i8.i64(i8* align 1 %ptr, i8* align 1 %1, i64 4, i1 false)
+  ret void
+}
Index: lib/CodeGen/SafeStack.cpp
===================================================================
--- lib/CodeGen/SafeStack.cpp
+++ lib/CodeGen/SafeStack.cpp
@@ -260,8 +260,14 @@
 bool SafeStack::IsMemIntrinsicSafe(const MemIntrinsic *MI, const Use &U,
                                    const Value *AllocaPtr,
                                    uint64_t AllocaSize) {
-  // All MemIntrinsics have destination address in Arg0 and size in Arg2.
-  if (MI->getRawDest() != U) return true;
+  if (auto MTI = dyn_cast<MemTransferInst>(MI)) {
+    if (MTI->getRawSource() != U && MTI->getRawDest() != U)
+      return true;
+  } else {
+    if (MI->getRawDest() != U)
+      return true;
+  }
+
   const auto *Len = dyn_cast<ConstantInt>(MI->getLength());
   // Non-constant size => unsafe. FIXME: try SCEV getRange.
   if (!Len) return false;


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