From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754757AbaENKzA (ORCPT ); Wed, 14 May 2014 06:55:00 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44553 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753956AbaENKy7 (ORCPT ); Wed, 14 May 2014 06:54:59 -0400 Message-ID: <53734B7D.4010504@redhat.com> Date: Wed, 14 May 2014 11:54:53 +0100 From: Pedro Alves User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Anshuman Khandual CC: linux-kernel@vger.kernel.org, hpa@zytor.com, suresh.b.siddha@intel.com Subject: [PATCH v2] ptrace: Clarify PTRACE_GETREGSET/PTRACE_SETREGSET, documentation in uapi header References: <1398682853-7541-1-git-send-email-khandual@linux.vnet.ibm.com> <53625681.8010905@redhat.com> <53670F35.6010502@linux.vnet.ibm.com> <53725FF6.6060004@redhat.com> <537316DB.4060701@linux.vnet.ibm.com> In-Reply-To: <537316DB.4060701@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05/14/14 08:10, Anshuman Khandual wrote: > On 05/13/2014 11:39 PM, Pedro Alves wrote: >> On 05/05/14 05:10, Anshuman Khandual wrote: >>> On 05/01/2014 07:43 PM, Pedro Alves wrote: >> OK, then this is what I suggest instead: ... >>> Shall I resend the patch with the your proposed changes and your "Signed-off-by" and >>> moving myself as "Reported-by" ? >> >> No idea of the actual policy to follow. Feel free to do that if that's the >> standard procedure. > > Even I am not sure about this, so to preserve the correct authorship, would you > mind sending this patch ? Here you go. This is against current Linus'. Please take it from here if necessary. 8<------------------------------------------ >>From 1237f5ac5896f3910f66df83a5093bb548006188 Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Wed, 14 May 2014 11:05:07 +0100 Subject: [PATCH] ptrace: Clarify PTRACE_GETREGSET/PTRACE_SETREGSET documentation in uapi header The current comments don't explicitly state in plain words that iov.len must be set to the buffer's length prior to the ptrace call. A user might get confused and leave that uninitialized. In the ptrace_regset function (snippet below) we see that the buffer length has to be a multiple of the slot/register size for the given NT_XXX_TYPE: if (!regset || (kiov->iov_len % regset->size) != 0) return -EINVAL; Note regset->size is the size of each slot/register in the set, not the size of the whole set. And then, we see here: kiov->iov_len = min(kiov->iov_len, (__kernel_size_t) (regset->n * regset->size)); that the kernel takes care of capping the requested length to the size of the whole regset. Signed-off-by: Pedro Alves Reported-by: Anshuman Khandual --- include/uapi/linux/ptrace.h | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h index cf1019e..30836b9 100644 --- a/include/uapi/linux/ptrace.h +++ b/include/uapi/linux/ptrace.h @@ -39,12 +39,17 @@ * payload are exactly the same layout. * * This interface usage is as follows: - * struct iovec iov = { buf, len}; + * struct iovec iov = { buf, len }; * * ret = ptrace(PTRACE_GETREGSET/PTRACE_SETREGSET, pid, NT_XXX_TYPE, &iov); * - * On the successful completion, iov.len will be updated by the kernel, - * specifying how much the kernel has written/read to/from the user's iov.buf. + * On entry, iov describes the buffer's address and length. The buffer's length + * must be a multiple of the size of a single register in the register set. The + * kernel never reads or writes more than iov.len, and caps the buffer length to + * the register set's size. In other words, the kernel reads or writes + * min(iov.len, regset size). On successful completion, iov.len is updated by + * the kernel, specifying how much the kernel has read from / written to the + * user's iov.buf. */ #define PTRACE_GETREGSET 0x4204 #define PTRACE_SETREGSET 0x4205 -- 1.9.0