[RISCV] Fix AddressSanitizer heap-buffer-overflow in disassembling

Summary:
RISCVDisassembler should check number of bytes available before reading them.
Crash noticed when enabling -DLLVM_USE_SANITIZER=Address.

This bug was uncovered by a LLVM MC Disassembler Protocol Buffer Fuzzer for the RISC-V assembly language.

Reviewers: asb

Reviewed By: asb

Subscribers: rbar, johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217, zzheng, edward-jones, mgrang, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe, PkmX, jocewei, asb

Differential Revision: https://reviews.llvm.org/D51708

llvm-svn: 341686

llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp

@@ -257,11 +257,19 @@ DecodeStatus RISCVDisassembler::getInstruction(MCInst &MI, uint64_t &Size,
 
   // It's a 32 bit instruction if bit 0 and 1 are 1.
   if ((Bytes[0] & 0x3) == 0x3) {
+    if (Bytes.size() < 4) {
+      Size = 0;
+      return MCDisassembler::Fail;
+    }
     Insn = support::endian::read32le(Bytes.data());
     LLVM_DEBUG(dbgs() << "Trying RISCV32 table :\n");
     Result = decodeInstruction(DecoderTable32, MI, Insn, Address, this, STI);
     Size = 4;
   } else {
+    if (Bytes.size() < 2) {
+      Size = 0;
+      return MCDisassembler::Fail;
+    }
     Insn = support::endian::read16le(Bytes.data());
 
     if (!STI.getFeatureBits()[RISCV::Feature64Bit]) {

llvm/test/MC/Disassembler/RISCV/fuzzer-invalid.txt

@@ -0,0 +1,8 @@
+# RUN: not llvm-mc -disassemble -triple=riscv32 < %s 2>&1 | FileCheck %s
+# RUN: not llvm-mc -disassemble -triple=riscv64 < %s 2>&1 | FileCheck %s
+#
+# Test generated by a LLVM MC Disassembler Protocol Buffer Fuzzer
+# for the RISC-V assembly language.
+
+[0xf9 0x95 0xab 0x99]
+# CHECK: warning: invalid instruction encoding

llvm/test/MC/Disassembler/RISCV/lit.local.cfg

@@ -0,0 +1,3 @@
+if not 'RISCV' in config.root.targets:
+    config.unsupported = True
+