[Backport] Security Bug 919572

Enfore valid register for SignExtendWord8ToInt32.

On ia32, the instruction selector uses movsx_b to compile the wasm
SignExtendWord8ToInt32 instruction. movsx_b requires a byte register
as input. However, not all allocatable registers on ia32 are. As we
cannot currently express constraints on subsets of registers, this
change now forces the input to movsx_b into eax.

Bug: chromium:919572
Change-Id: I40b128958b5994bdcba5c313a8d5f1986565fa64
Reviewed-by: Michael Brüning <michael.bruning@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

1 files changed, 5 insertions, 1 deletions

diff --git a/chromium/v8/src/compiler/ia32/instruction-selector-ia32.cc b/chromium/v8/src/compiler/ia32/instruction-selector-ia32.cc
index c827c68a5ff..01d0babf7dc 100644
--- a/chromium/v8/src/compiler/ia32/instruction-selector-ia32.cc
+++ b/chromium/v8/src/compiler/ia32/instruction-selector-ia32.cc
@@ -169,7 +169,11 @@ namespace {
 
 void VisitRO(InstructionSelector* selector, Node* node, ArchOpcode opcode) {
   IA32OperandGenerator g(selector);
-  selector->Emit(opcode, g.DefineAsRegister(node), g.Use(node->InputAt(0)));
+  Node* input = node->InputAt(0);
+  // We have to use a byte register as input to movsxb.
+  InstructionOperand input_op =
+      opcode == kIA32Movsxbl ? g.UseFixed(input, eax) : g.Use(input);
+  selector->Emit(opcode, g.DefineAsRegister(node), input_op);
 }