From: Nadav Amit Date: Thu, 2 Oct 2014 22:10:04 +0000 (+0300) Subject: KVM: x86: Decoding guest instructions which cross page boundary may fail X-Git-Tag: v3.18-rc2~6^2~6 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=08da44aedba0f493e10695fa334348a7a4f72eb3;p=linux.git 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. Cc: stable@vger.kernel.org Fixes: 5cfc7e0f5e5e1adf998df94f8e36edaf5d30d38e Signed-off-by: Nadav Amit Signed-off-by: Paolo Bonzini --- diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index c0deaff8d9f0..02c8ea804aaf 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -778,8 +778,10 @@ static int __do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, int op_size) static __always_inline int do_insn_fetch_bytes(struct x86_emulate_ctxt *ctxt, unsigned size) { - if (unlikely(ctxt->fetch.end - ctxt->fetch.ptr < size)) - return __do_insn_fetch_bytes(ctxt, size); + unsigned done_size = ctxt->fetch.end - ctxt->fetch.ptr; + + if (unlikely(done_size < size)) + return __do_insn_fetch_bytes(ctxt, size - done_size); else return X86EMUL_CONTINUE; }