From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756163AbaJHONZ (ORCPT ); Wed, 8 Oct 2014 10:13:25 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:43707 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753074AbaJHONY (ORCPT ); Wed, 8 Oct 2014 10:13:24 -0400 Date: Wed, 8 Oct 2014 15:13:06 +0100 From: Will Deacon To: AKASHI Takahiro Cc: "keescook@chromium.org" , Catalin Marinas , "dsaxena@linaro.org" , "arndb@arndb.de" , "linux-arm-kernel@lists.infradead.org" , "linaro-kernel@lists.linaro.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v7 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL Message-ID: <20141008141306.GQ26140@arm.com> References: <1412243176-16192-1-git-send-email-takahiro.akashi@linaro.org> <1412243176-16192-2-git-send-email-takahiro.akashi@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1412243176-16192-2-git-send-email-takahiro.akashi@linaro.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Akashi, On Thu, Oct 02, 2014 at 10:46:11AM +0100, AKASHI Takahiro wrote: > To allow tracer to be able to change/skip a system call by re-writing > a syscall number, there are several approaches: > > (1) modify x8 register with ptrace(PTRACE_SETREGSET), and handle this case > later on in syscall_trace_enter(), or > (2) support ptrace(PTRACE_SET_SYSCALL) as on arm > > Thinking of the fact that user_pt_regs doesn't expose 'syscallno' to > tracer as well as that secure_computing() expects a changed syscall number > to be visible, especially case of -1, before this function returns in > syscall_trace_enter(), we'd better take (2). > > Reviewed-by: Kees Cook > Signed-off-by: AKASHI Takahiro > --- > arch/arm64/include/uapi/asm/ptrace.h | 1 + > arch/arm64/kernel/ptrace.c | 14 +++++++++++++- > 2 files changed, 14 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h > index 6913643..49c6174 100644 > --- a/arch/arm64/include/uapi/asm/ptrace.h > +++ b/arch/arm64/include/uapi/asm/ptrace.h > @@ -23,6 +23,7 @@ > > #include > > +#define PTRACE_SET_SYSCALL 23 > > /* > * PSR bits > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c > index fe63ac5..2842f9f 100644 > --- a/arch/arm64/kernel/ptrace.c > +++ b/arch/arm64/kernel/ptrace.c > @@ -1082,7 +1082,19 @@ const struct user_regset_view *task_user_regset_view(struct task_struct *task) > long arch_ptrace(struct task_struct *child, long request, > unsigned long addr, unsigned long data) > { > - return ptrace_request(child, request, addr, data); > + int ret; > + > + switch (request) { > + case PTRACE_SET_SYSCALL: > + task_pt_regs(child)->syscallno = data; > + ret = 0; > + break; > + default: > + ret = ptrace_request(child, request, addr, data); > + break; > + } > + > + return ret; > } I still don't understand why this needs to be in arch-specific code. Can't we implement this in generic code and get architectures to implement something like syscall_set_nr if they want the generic interface? Will