From: Will Deacon <will.deacon@arm.com> To: Kees Cook <keescook@chromium.org> Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>, Roman Peniaev <r.peniaev@gmail.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Marc Zyngier <Marc.Zyngier@arm.com>, Catalin Marinas <Catalin.Marinas@arm.com>, Sekhar Nori <nsekhar@ti.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "stable@vger.kernel.org" <stable@vger.kernel.org>, Christoffer Dall <christoffer.dall@linaro.org>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH 1/2] ARM: entry-common: fix forgotten set of thread_info->syscall Date: Mon, 19 Jan 2015 09:20:03 +0000 [thread overview] Message-ID: <20150119092002.GA32131@arm.com> (raw) In-Reply-To: <CAGXu5j+9p1T29NoHnCNywd0T=H2mzWhCou5nSRfXZktEOC7_=A@mail.gmail.com> On Fri, Jan 16, 2015 at 11:54:45PM +0000, Kees Cook wrote: > On Fri, Jan 16, 2015 at 11:57 AM, Kees Cook <keescook@chromium.org> wrote: > > On Fri, Jan 16, 2015 at 8:17 AM, Russell King - ARM Linux > > <linux@arm.linux.org.uk> wrote: > >> On Sat, Jan 17, 2015 at 01:08:11AM +0900, Roman Peniaev wrote: > >>> On Sat, Jan 17, 2015 at 12:59 AM, Russell King - ARM Linux > >>> <linux@arm.linux.org.uk> wrote: > >>> > On Sat, Jan 17, 2015 at 12:57:02AM +0900, Roman Peniaev wrote: > >>> >> On Fri, Jan 16, 2015 at 7:54 AM, Kees Cook <keescook@chromium.org> wrote: > >>> >> > One interesting thing I noticed (which is unchanged by this series), > >>> >> > but pulling ARM_r7 during the seccomp ptrace event shows __NR_poll, > >>> >> > not __NR_restart_syscall, even though it was a __NR_restart_syscall > >>> >> > trap from seccomp. Is there a better place to see the actual syscall? > >>> >> > >>> >> As I understand we do not push new r7 to the stack, and ptrace uses the > >>> >> old value. > >>> > > >>> > And why should we push r7 to the stack? ptrace should be using the > >>> > recorded system call number, rather than poking about on the stack > >>> > itself. > >>> > >>> Probably we should not, but the behaviour comparing arm to x86 is different. > >> > >> We definitely should not, because changing the stacked value changes the > >> value in r7 after the syscall has returned. We have guaranteed that the > >> value will be preserved across syscalls for years, so we really should > >> not be changing that. > > > > Yeah, we can't mess with the registers. I was just asking for > > clarification on how this is visible to userspace. > > > >> > >>> Also there is no any way from userspace to figure out what syscall was > >>> restarted, if you do not trace each syscall enter and exit from the > >>> very beginning. > >> > >> Thinking about ptrace, that's been true for years. > >> > >> It really depends whether you consider the restart syscall a userspace > >> thing or a kernelspace thing. When you consider that the vast majority > >> of syscall restarts are done internally in the kernel, and we just > >> re-issue the syscall, it immediately brings up the question "why is > >> the restart block method different?" and "should the restart block > >> method be visible to userspace?" > >> > >> IMHO, it is prudent not to expose kernel internals to userspace unless > >> there is a real reason to, otherwise they become part of the userspace > >> API. > > > > I couldn't agree more, but restart_syscall is already visible to > > userspace: it can be called directly, for example. And it's visible to > > tracers. > > > > Unfortunately, the difference here is the visibility during trace > > trap. On x86, it's exposed but on ARM, there's no way (that I can > > find) to query the "true" syscall, even though the true syscall is > > what triggers the tracer. The syscall number isn't provided by any > > element of the ptrace event system, nor through siginfo, and must be > > examined on a per-arch basis from registers. > > > > Seccomp does, however, provide a mechanism to pass arbitrary event > > data on a TRACE event, so poll vs restart_syscall can be distinguished > > that way. > > > > It seems even strace doesn't know how to find this information. For example: > > > > x86: > > poll([{fd=3, events=POLLIN}], 1, 4294967295 > > ) = ? ERESTART_RESTARTBLOCK (Interrupted by signal) > > --- SIGSTOP {si_signo=SIGSTOP, si_code=SI_USER, si_pid=994, si_uid=1000} --- > > --- stopped by SIGSTOP --- > > --- SIGCONT {si_signo=SIGCONT, si_code=SI_USER, si_pid=994, si_uid=1000} --- > > restart_syscall(<... resuming interrupted call ...> > > > > ARM: > > poll([{fd=3, events=POLLIN}], 1, -1 > > ) = ? ERESTART_RESTARTBLOCK (Interrupted by signal) > > --- SIGSTOP {si_signo=SIGSTOP, si_code=SI_USER, si_pid=20563, si_uid=0} --- > > --- stopped by SIGSTOP --- > > --- SIGCONT {si_signo=SIGCONT, si_code=SI_USER, si_pid=20563, si_uid=0} --- > > poll([{fd=3, events=POLLIN}], 1, -1 > > > > Would it make sense to add REGSET_SYSTEM_CALL to ARM? (Though this > > begs the question, "Is restart_syscall visible during a trace on > > arm64?", which I'll have to go check...) > > So, some further testing: > - native arm64 presents "poll" again even to seccomp when > restart_syscall is triggered (both via regs[8] and > NT_ARM_SYSTEM_CALL). I'm fine either way for the native case, but we should stick with whetever we end up with. Being compatible with ARM is probably a good idea. Do you have a preference? > - compat mode on arm64 _does_ show syscall_restart (via ARM_r7). That sounds like a bug, then. Any chance you could look into a patch? Will
WARNING: multiple messages have this Message-ID (diff)
From: will.deacon@arm.com (Will Deacon) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 1/2] ARM: entry-common: fix forgotten set of thread_info->syscall Date: Mon, 19 Jan 2015 09:20:03 +0000 [thread overview] Message-ID: <20150119092002.GA32131@arm.com> (raw) In-Reply-To: <CAGXu5j+9p1T29NoHnCNywd0T=H2mzWhCou5nSRfXZktEOC7_=A@mail.gmail.com> On Fri, Jan 16, 2015 at 11:54:45PM +0000, Kees Cook wrote: > On Fri, Jan 16, 2015 at 11:57 AM, Kees Cook <keescook@chromium.org> wrote: > > On Fri, Jan 16, 2015 at 8:17 AM, Russell King - ARM Linux > > <linux@arm.linux.org.uk> wrote: > >> On Sat, Jan 17, 2015 at 01:08:11AM +0900, Roman Peniaev wrote: > >>> On Sat, Jan 17, 2015 at 12:59 AM, Russell King - ARM Linux > >>> <linux@arm.linux.org.uk> wrote: > >>> > On Sat, Jan 17, 2015 at 12:57:02AM +0900, Roman Peniaev wrote: > >>> >> On Fri, Jan 16, 2015 at 7:54 AM, Kees Cook <keescook@chromium.org> wrote: > >>> >> > One interesting thing I noticed (which is unchanged by this series), > >>> >> > but pulling ARM_r7 during the seccomp ptrace event shows __NR_poll, > >>> >> > not __NR_restart_syscall, even though it was a __NR_restart_syscall > >>> >> > trap from seccomp. Is there a better place to see the actual syscall? > >>> >> > >>> >> As I understand we do not push new r7 to the stack, and ptrace uses the > >>> >> old value. > >>> > > >>> > And why should we push r7 to the stack? ptrace should be using the > >>> > recorded system call number, rather than poking about on the stack > >>> > itself. > >>> > >>> Probably we should not, but the behaviour comparing arm to x86 is different. > >> > >> We definitely should not, because changing the stacked value changes the > >> value in r7 after the syscall has returned. We have guaranteed that the > >> value will be preserved across syscalls for years, so we really should > >> not be changing that. > > > > Yeah, we can't mess with the registers. I was just asking for > > clarification on how this is visible to userspace. > > > >> > >>> Also there is no any way from userspace to figure out what syscall was > >>> restarted, if you do not trace each syscall enter and exit from the > >>> very beginning. > >> > >> Thinking about ptrace, that's been true for years. > >> > >> It really depends whether you consider the restart syscall a userspace > >> thing or a kernelspace thing. When you consider that the vast majority > >> of syscall restarts are done internally in the kernel, and we just > >> re-issue the syscall, it immediately brings up the question "why is > >> the restart block method different?" and "should the restart block > >> method be visible to userspace?" > >> > >> IMHO, it is prudent not to expose kernel internals to userspace unless > >> there is a real reason to, otherwise they become part of the userspace > >> API. > > > > I couldn't agree more, but restart_syscall is already visible to > > userspace: it can be called directly, for example. And it's visible to > > tracers. > > > > Unfortunately, the difference here is the visibility during trace > > trap. On x86, it's exposed but on ARM, there's no way (that I can > > find) to query the "true" syscall, even though the true syscall is > > what triggers the tracer. The syscall number isn't provided by any > > element of the ptrace event system, nor through siginfo, and must be > > examined on a per-arch basis from registers. > > > > Seccomp does, however, provide a mechanism to pass arbitrary event > > data on a TRACE event, so poll vs restart_syscall can be distinguished > > that way. > > > > It seems even strace doesn't know how to find this information. For example: > > > > x86: > > poll([{fd=3, events=POLLIN}], 1, 4294967295 > > ) = ? ERESTART_RESTARTBLOCK (Interrupted by signal) > > --- SIGSTOP {si_signo=SIGSTOP, si_code=SI_USER, si_pid=994, si_uid=1000} --- > > --- stopped by SIGSTOP --- > > --- SIGCONT {si_signo=SIGCONT, si_code=SI_USER, si_pid=994, si_uid=1000} --- > > restart_syscall(<... resuming interrupted call ...> > > > > ARM: > > poll([{fd=3, events=POLLIN}], 1, -1 > > ) = ? ERESTART_RESTARTBLOCK (Interrupted by signal) > > --- SIGSTOP {si_signo=SIGSTOP, si_code=SI_USER, si_pid=20563, si_uid=0} --- > > --- stopped by SIGSTOP --- > > --- SIGCONT {si_signo=SIGCONT, si_code=SI_USER, si_pid=20563, si_uid=0} --- > > poll([{fd=3, events=POLLIN}], 1, -1 > > > > Would it make sense to add REGSET_SYSTEM_CALL to ARM? (Though this > > begs the question, "Is restart_syscall visible during a trace on > > arm64?", which I'll have to go check...) > > So, some further testing: > - native arm64 presents "poll" again even to seccomp when > restart_syscall is triggered (both via regs[8] and > NT_ARM_SYSTEM_CALL). I'm fine either way for the native case, but we should stick with whetever we end up with. Being compatible with ARM is probably a good idea. Do you have a preference? > - compat mode on arm64 _does_ show syscall_restart (via ARM_r7). That sounds like a bug, then. Any chance you could look into a patch? Will
next prev parent reply other threads:[~2015-01-19 9:20 UTC|newest] Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-01-11 14:32 [PATCH 0/2] ARM: set thread_info->syscall just before sys_* execution Roman Pen 2015-01-11 14:32 ` Roman Pen 2015-01-11 14:32 ` [PATCH 1/2] ARM: entry-common: fix forgotten set of thread_info->syscall Roman Pen 2015-01-11 14:32 ` Roman Pen 2015-01-12 18:39 ` Will Deacon 2015-01-12 18:39 ` Will Deacon 2015-01-12 18:39 ` Will Deacon 2015-01-13 8:35 ` Roman Peniaev 2015-01-13 8:35 ` Roman Peniaev 2015-01-13 8:35 ` Roman Peniaev 2015-01-14 2:23 ` Roman Peniaev 2015-01-14 2:23 ` Roman Peniaev 2015-01-14 2:23 ` Roman Peniaev 2015-01-14 20:51 ` Kees Cook 2015-01-14 20:51 ` Kees Cook 2015-01-14 20:51 ` Kees Cook 2015-01-15 1:54 ` Roman Peniaev 2015-01-15 1:54 ` Roman Peniaev 2015-01-15 1:54 ` Roman Peniaev 2015-01-15 22:54 ` Kees Cook 2015-01-15 22:54 ` Kees Cook 2015-01-15 22:54 ` Kees Cook 2015-01-16 15:57 ` Roman Peniaev 2015-01-16 15:57 ` Roman Peniaev 2015-01-16 15:57 ` Roman Peniaev 2015-01-16 15:59 ` Russell King - ARM Linux 2015-01-16 15:59 ` Russell King - ARM Linux 2015-01-16 15:59 ` Russell King - ARM Linux 2015-01-16 16:08 ` Roman Peniaev 2015-01-16 16:08 ` Roman Peniaev 2015-01-16 16:08 ` Roman Peniaev 2015-01-16 16:17 ` Russell King - ARM Linux 2015-01-16 16:17 ` Russell King - ARM Linux 2015-01-16 16:17 ` Russell King - ARM Linux 2015-01-16 19:57 ` Kees Cook 2015-01-16 19:57 ` Kees Cook 2015-01-16 19:57 ` Kees Cook 2015-01-16 23:54 ` Kees Cook 2015-01-16 23:54 ` Kees Cook 2015-01-16 23:54 ` Kees Cook 2015-01-19 5:58 ` Roman Peniaev 2015-01-19 5:58 ` Roman Peniaev 2015-01-19 5:58 ` Roman Peniaev 2015-01-20 18:56 ` Kees Cook 2015-01-20 18:56 ` Kees Cook 2015-01-20 18:56 ` Kees Cook 2015-01-19 9:20 ` Will Deacon [this message] 2015-01-19 9:20 ` Will Deacon 2015-01-19 9:20 ` Will Deacon 2015-01-20 18:31 ` Kees Cook 2015-01-20 18:31 ` Kees Cook 2015-01-20 18:31 ` Kees Cook 2015-01-20 22:45 ` Russell King - ARM Linux 2015-01-20 22:45 ` Russell King - ARM Linux 2015-01-20 22:45 ` Russell King - ARM Linux 2015-01-20 23:04 ` Russell King - ARM Linux 2015-01-20 23:04 ` Russell King - ARM Linux 2015-01-20 23:04 ` Russell King - ARM Linux 2015-01-21 23:32 ` Kees Cook 2015-01-21 23:32 ` Kees Cook 2015-01-21 23:32 ` Kees Cook 2015-01-22 1:24 ` Roman Peniaev 2015-01-22 1:24 ` Roman Peniaev 2015-01-22 1:24 ` Roman Peniaev 2015-01-22 18:07 ` Kees Cook 2015-01-22 18:07 ` Kees Cook 2015-01-22 18:07 ` Kees Cook 2015-01-23 4:17 ` Roman Peniaev 2015-01-23 4:17 ` Roman Peniaev 2015-01-23 4:17 ` Roman Peniaev 2015-01-11 14:32 ` [PATCH 2/2] ARM: entry-common,ptrace: do not pass scno to syscall_trace_enter Roman Pen 2015-01-11 14:32 ` [PATCH 2/2] ARM: entry-common, ptrace: " Roman Pen 2015-01-13 20:08 ` [PATCH 2/2] ARM: entry-common,ptrace: " Kees Cook 2015-01-13 20:08 ` [PATCH 2/2] ARM: entry-common, ptrace: " Kees Cook 2015-01-13 23:21 ` [PATCH 2/2] ARM: entry-common,ptrace: " Roman Peniaev 2015-01-13 23:21 ` [PATCH 2/2] ARM: entry-common, ptrace: " Roman Peniaev 2015-01-13 23:43 ` [PATCH 2/2] ARM: entry-common,ptrace: " Kees Cook 2015-01-13 23:43 ` [PATCH 2/2] ARM: entry-common, ptrace: " Kees Cook
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