From mboxrd@z Thu Jan 1 00:00:00 1970 From: takahiro.akashi@linaro.org (AKASHI Takahiro) Date: Wed, 27 Aug 2014 14:32:44 +0900 Subject: [PATCH v6 1/6] arm64: ptrace: add PTRACE_SET_SYSCALL In-Reply-To: <20140826174637.GC23445@arm.com> References: <1408611405-8943-1-git-send-email-takahiro.akashi@linaro.org> <1408611405-8943-2-git-send-email-takahiro.akashi@linaro.org> <53F68C81.6020807@linaro.org> <20140826174637.GC23445@arm.com> Message-ID: <53FD6D7C.8030700@linaro.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Kees, On 08/27/2014 02:46 AM, Will Deacon wrote: > On Fri, Aug 22, 2014 at 01:19:13AM +0100, AKASHI Takahiro wrote: >> On 08/22/2014 01:47 AM, Kees Cook wrote: >>> On Thu, Aug 21, 2014 at 3:56 AM, 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). >>>> >>>> Signed-off-by: AKASHI Takahiro >>> >>> Thanks, I like having this on both arm and arm64. >> >> Yeah, having this simplified the code of syscall_trace_enter() a bit, but >> also imposes some restriction on arm64, too. >> >> > I wonder if other archs should add this option too. >> >> Do you think so? I assumed that SET_SYSCALL is to be avoided if possible. >> >> I also think that SET_SYSCALL should take an extra argument for a return value >> just in case of -1 (or we have SKIP_SYSCALL?). > > I think we should propose this as a new request in the generic ptrace code. > We can have an architecture-hook for actually setting the syscall, and allow > architectures to define their own implementation of the request so they can > be moved over one by one. What do you think about this request? -Takahiro AKASHI > Will >