From mboxrd@z Thu Jan 1 00:00:00 1970 From: luto@amacapital.net (Andy Lutomirski) Date: Wed, 23 Jul 2014 20:54:00 -0700 Subject: [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations In-Reply-To: <1406020499-5537-2-git-send-email-takahiro.akashi@linaro.org> References: <1406020499-5537-1-git-send-email-takahiro.akashi@linaro.org> <1406020499-5537-2-git-send-email-takahiro.akashi@linaro.org> Message-ID: <53D08358.4020902@amacapital.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 07/22/2014 02:14 AM, AKASHI Takahiro wrote: > Arm64 holds a syscall number in w8(x8) register. Ptrace tracer may change > its value either to: > * any valid syscall number to alter a system call, or > * -1 to skip a system call > > This patch implements this behavior by reloading that value into syscallno > in struct pt_regs after tracehook_report_syscall_entry() or > secure_computing(). In case of '-1', a return value of system call can also > be changed by the tracer setting the value to x0 register, and so > sys_ni_nosyscall() should not be called. > > See also: > 42309ab4, ARM: 8087/1: ptrace: reload syscall number after > secure_computing() check > > Signed-off-by: AKASHI Takahiro > --- > arch/arm64/kernel/entry.S | 2 ++ > arch/arm64/kernel/ptrace.c | 13 +++++++++++++ > 2 files changed, 15 insertions(+) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 5141e79..de8bdbc 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -628,6 +628,8 @@ ENDPROC(el0_svc) > __sys_trace: > mov x0, sp > bl syscall_trace_enter > + cmp w0, #-1 // skip syscall? > + b.eq ret_to_user Does this mean that skipped syscalls will cause exit tracing to be skipped? If so, then you risk (at least) introducing a nice user-triggerable OOPS if audit is enabled. This bug existed for *years* on x86_32, and it amazes me that no one ever triggered it by accident. (Grr, audit.) --Andy From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934159AbaGXDyJ (ORCPT ); Wed, 23 Jul 2014 23:54:09 -0400 Received: from mail-pa0-f43.google.com ([209.85.220.43]:44192 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934119AbaGXDyE (ORCPT ); Wed, 23 Jul 2014 23:54:04 -0400 Message-ID: <53D08358.4020902@amacapital.net> Date: Wed, 23 Jul 2014 20:54:00 -0700 From: Andy Lutomirski User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: AKASHI Takahiro , wad@chromium.org, catalin.marinas@arm.com, will.deacon@arm.com, keescook@chromium.org CC: dsaxena@linaro.org, linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/3] arm64: ptrace: reload a syscall number after ptrace operations References: <1406020499-5537-1-git-send-email-takahiro.akashi@linaro.org> <1406020499-5537-2-git-send-email-takahiro.akashi@linaro.org> In-Reply-To: <1406020499-5537-2-git-send-email-takahiro.akashi@linaro.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/22/2014 02:14 AM, AKASHI Takahiro wrote: > Arm64 holds a syscall number in w8(x8) register. Ptrace tracer may change > its value either to: > * any valid syscall number to alter a system call, or > * -1 to skip a system call > > This patch implements this behavior by reloading that value into syscallno > in struct pt_regs after tracehook_report_syscall_entry() or > secure_computing(). In case of '-1', a return value of system call can also > be changed by the tracer setting the value to x0 register, and so > sys_ni_nosyscall() should not be called. > > See also: > 42309ab4, ARM: 8087/1: ptrace: reload syscall number after > secure_computing() check > > Signed-off-by: AKASHI Takahiro > --- > arch/arm64/kernel/entry.S | 2 ++ > arch/arm64/kernel/ptrace.c | 13 +++++++++++++ > 2 files changed, 15 insertions(+) > > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S > index 5141e79..de8bdbc 100644 > --- a/arch/arm64/kernel/entry.S > +++ b/arch/arm64/kernel/entry.S > @@ -628,6 +628,8 @@ ENDPROC(el0_svc) > __sys_trace: > mov x0, sp > bl syscall_trace_enter > + cmp w0, #-1 // skip syscall? > + b.eq ret_to_user Does this mean that skipped syscalls will cause exit tracing to be skipped? If so, then you risk (at least) introducing a nice user-triggerable OOPS if audit is enabled. This bug existed for *years* on x86_32, and it amazes me that no one ever triggered it by accident. (Grr, audit.) --Andy