Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932480AbaDXRIl (ORCPT ); Thu, 24 Apr 2014 13:08:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:17309 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932410AbaDXRIh (ORCPT ); Thu, 24 Apr 2014 13:08:37 -0400 From: Denys Vlasenko To: linux-kernel@vger.kernel.org Cc: Denys Vlasenko , Oleg Nesterov Subject: [PATCH] uprobes/x86: Refuse to attach uprobe to "word-sized" branch insns Date: Thu, 24 Apr 2014 19:08:24 +0200 Message-Id: <1398359304-26472-1-git-send-email-dvlasenk@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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/