Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758741AbaDXRdy (ORCPT ); Thu, 24 Apr 2014 13:33:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:62336 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758534AbaDXRds (ORCPT ); Thu, 24 Apr 2014 13:33:48 -0400 Date: Thu, 24 Apr 2014 19:33:33 +0200 From: Oleg Nesterov To: Denys Vlasenko Cc: linux-kernel@vger.kernel.org, Masami Hiramatsu , Jim Keniston , Ingo Molnar Subject: Re: [PATCH] uprobes/x86: Refuse to attach uprobe to "word-sized" branch insns Message-ID: <20140424173333.GA416@redhat.com> References: <1398359304-26472-1-git-send-email-dvlasenk@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1398359304-26472-1-git-send-email-dvlasenk@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Thanks! Masami, Jim, any acks? On 04/24, Denys Vlasenko wrote: > > All branch insns on x86 can be prefixed with the operand-size > override prefix, 0x66. It was only ever useful for performing > jumps to 32-bit offsets in 16-bit code segments. > > In 32-bit code, such instructions are useless since > they cause IP truncation to 16 bits, and in case of call insns, > they save only 16 bits of return address and misalign > the stack pointer as a "bonus". > > In 64-bit code, such instructions are treated differently by Intel > and AMD CPUs: Intel ignores the prefix altogether, > AMD treats them the same as in 32-bit mode. > > Before this patch, the emulation code would execute > the instructions as if they have no 0x66 prefix. > > With this patch, we refuse to attach uprobes to such insns. > > Signed-off-by: Denys Vlasenko > Cc: Oleg Nesterov > --- > arch/x86/kernel/uprobes.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c > index ace2291..29b152d 100644 > --- a/arch/x86/kernel/uprobes.c > +++ b/arch/x86/kernel/uprobes.c > @@ -582,6 +582,7 @@ static struct uprobe_xol_ops branch_xol_ops = { > /* Returns -ENOSYS if branch_xol_ops doesn't handle this insn */ > static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn) > { > + int i; > u8 opc1 = OPCODE1(insn); > > /* has the side-effect of processing the entire instruction */ > @@ -612,6 +613,17 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn) > return -ENOSYS; > } > > + /* > + * 16-bit overrides such as CALLW (66 e8 nn nn) are not supported. > + * Intel and AMD behavior differ in 64-bit mode: Intel ignores 66 prefix. > + * No one uses these insns. > + * Reject any branch insns with such prefix. > + */ > + for (i = 0; i < insn->prefixes.nbytes; i++) { > + if (insn->prefixes.bytes[i] == 0x66) > + return -ENOTSUPP; > + } > + > auprobe->branch.opc1 = opc1; > auprobe->branch.ilen = insn->length; > auprobe->branch.offs = insn->immediate.value; > -- > 1.8.1.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/