KVM: x86: Decoding guest instructions which cross page boundary may fail

Once an instruction crosses a page boundary, the size read from the second page disregards the common case that part of the operand resides on the first page. As a result, fetch of long insturctions may fail, and thereby cause the decoding to fail as well.

Nadav Amit committed 12 years ago

Commit 08da44a1 parent 2bc19dc1 file · +4 −2Browse files

Unified · Split

arch/x86/kvm/emulate.c+4−2

@@ -778,8 +778,10 @@ static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size) · 777 unmodified lines
778	static __always_inline int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt,	778	static __always_inline int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt,
779	unsigned size)	779	unsigned size)
780	{	780	{
781	if (unlikely(ctxt->fetch.end - ctxt->fetch.ptr < size))	781	unsigned done_size = ctxt->fetch.end - ctxt->fetch.ptr;
782	return __do_insn_fetch_bytes(ctxt, size);	782
		783	if (unlikely(done_size < size))
		784	return __do_insn_fetch_bytes(ctxt, size - done_size);
783	else	785	else
784	return X86EMUL_CONTINUE;	786	return X86EMUL_CONTINUE;
785	}	787	}