| Message ID | 20200716193141.4068476-2-krisman@collabora.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Syscall User Redirection | expand |
On Thu, Jul 16, 2020 at 03:31:40PM -0400, Gabriel Krisman Bertazi wrote: > selector is an optional pointer to a char-sized userspace memory region > that has a key switch for the mechanism. This key switch is set to > either PR_SYS_DISPATCH_ON, PR_SYS_DISPATCH_OFF to enable and disable the > redirection without calling the kernel. > > The feature is meant to be set per-thread and it is disabled on > fork/clone/execv. Disabled on exec. Disabled in the child on clone/fork (and vfork, I think). That means we don't need to worry about it interacting badly with a setuid program, right?
On Thu, Jul 16, 2020 at 10:06:01PM +0100, Matthew Wilcox wrote: > On Thu, Jul 16, 2020 at 03:31:40PM -0400, Gabriel Krisman Bertazi wrote: > > selector is an optional pointer to a char-sized userspace memory region > > that has a key switch for the mechanism. This key switch is set to > > either PR_SYS_DISPATCH_ON, PR_SYS_DISPATCH_OFF to enable and disable the > > redirection without calling the kernel. > > > > The feature is meant to be set per-thread and it is disabled on > > fork/clone/execv. > > Disabled on exec. Disabled in the child on clone/fork (and vfork, I > think). > > That means we don't need to worry about it interacting badly with > a setuid program, right? Right, that's the intention.
On Thu, Jul 16, 2020 at 12:31 PM Gabriel Krisman Bertazi <krisman@collabora.com> wrote: > This is quite nice. I have a few comments, though: You mentioned rt_sigreturn(). Should this automatically exempt the kernel-provided signal restorer on architectures (e.g. x86_32) that provide one? The amount of syscall entry wiring that arches need to do is IMO already a bit out of hand. Should we instead rename TIF_SECCOMP to TIF_SYSCALL_INTERCEPTION and have one generic callback that handles seccomp and this new thing? > +int do_syscall_user_dispatch(struct pt_regs *regs) > +{ > + struct syscall_user_dispatch *sd = ¤t->syscall_dispatch; > + unsigned long ip = instruction_pointer(regs); > + char state; > + > + if (likely(ip >= sd->dispatcher_start && ip <= sd->dispatcher_end)) > + return 0; > + > + if (likely(sd->selector)) { > + if (unlikely(__get_user(state, sd->selector))) > + do_exit(SIGSEGV); > + > + if (likely(state == 0)) > + return 0; > + > + if (state != 1) > + do_exit(SIGSEGV); This seems a bit extreme and hard to debug if it ever happens.
Andy Lutomirski <luto@kernel.org> writes: > On Thu, Jul 16, 2020 at 12:31 PM Gabriel Krisman Bertazi > <krisman@collabora.com> wrote: >> > > This is quite nice. I have a few comments, though: > > You mentioned rt_sigreturn(). Should this automatically exempt the > kernel-provided signal restorer on architectures (e.g. x86_32) that > provide one? That seems reasonable. Not sure how easy it is to do it, though. > The amount of syscall entry wiring that arches need to do is IMO > already a bit out of hand. Should we instead rename TIF_SECCOMP to > TIF_SYSCALL_INTERCEPTION and have one generic callback that handles > seccomp and this new thing? Considering the previous suggestion from Kees to hide it inside the tracehook and Thomas rework of this path, I'm not sure what is the best solution here, but some rework of these flags is due. Thomas suggested expanding these flags to 64 bits and having some arch specific and arch-agnostic flags. With the storage expansion and arch-agnostic flags, would this still be desirable? >> +int do_syscall_user_dispatch(struct pt_regs *regs) >> +{ >> + struct syscall_user_dispatch *sd = ¤t->syscall_dispatch; >> + unsigned long ip = instruction_pointer(regs); >> + char state; >> + >> + if (likely(ip >= sd->dispatcher_start && ip <= sd->dispatcher_end)) >> + return 0; >> + >> + if (likely(sd->selector)) { >> + if (unlikely(__get_user(state, sd->selector))) >> + do_exit(SIGSEGV); >> + >> + if (likely(state == 0)) >> + return 0; >> + >> + if (state != 1) >> + do_exit(SIGSEGV); > > This seems a bit extreme and hard to debug if it ever happens. Makes sense, but I don't see a better way to return the error here. Maybe a SIGSYS with a different si_errno? Alternatively, we could revert to the previous behavior of allowing syscalls on state != 0, that existed in v1. What do you think?
On Thu, Jul 16, 2020 at 7:15 PM Gabriel Krisman Bertazi <krisman@collabora.com> wrote: > > Andy Lutomirski <luto@kernel.org> writes: > > > On Thu, Jul 16, 2020 at 12:31 PM Gabriel Krisman Bertazi > > <krisman@collabora.com> wrote: > >> > > > > This is quite nice. I have a few comments, though: > > > > You mentioned rt_sigreturn(). Should this automatically exempt the > > kernel-provided signal restorer on architectures (e.g. x86_32) that > > provide one? > > That seems reasonable. Not sure how easy it is to do it, though. For better or for worse, it's currently straightforward because the code is: __kernel_sigreturn: .LSTART_sigreturn: popl %eax /* XXX does this mean it needs unwind info? */ movl $__NR_sigreturn, %eax SYSCALL_ENTER_KERNEL and SYSCALL_ENTER_KERNEL is hardwired as int $0x80. (The latter is probably my fault, for better or for worse.) So this would change to: __vdso32_sigreturn_syscall: SYSCALL_ENTER_KERNEL and vdso2c would wire up __vdso32_sigreturn_syscall. Then there would be something like: bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs); and that would be that. Does anyone have an opinion as to whether this is a good idea? Modern glibc shouldn't be using this mechanism, I think, but I won't swear to it. > > > The amount of syscall entry wiring that arches need to do is IMO > > already a bit out of hand. Should we instead rename TIF_SECCOMP to > > TIF_SYSCALL_INTERCEPTION and have one generic callback that handles > > seccomp and this new thing? > > Considering the previous suggestion from Kees to hide it inside the > tracehook and Thomas rework of this path, I'm not sure what is the best > solution here, but some rework of these flags is due. Thomas suggested > expanding these flags to 64 bits and having some arch specific and > arch-agnostic flags. With the storage expansion and arch-agnostic flags, > would this still be desirable? I think it would be desirable to consolidate this to avoid having multiple arches need to separately wire up all of these mechanisms. I'm not sure that the initial upstream implementation needs this, but it might be nice to support this out of the box on all arches with seccomp support. > > >> +int do_syscall_user_dispatch(struct pt_regs *regs) > >> +{ > >> + struct syscall_user_dispatch *sd = ¤t->syscall_dispatch; > >> + unsigned long ip = instruction_pointer(regs); > >> + char state; > >> + > >> + if (likely(ip >= sd->dispatcher_start && ip <= sd->dispatcher_end)) > >> + return 0; > >> + > >> + if (likely(sd->selector)) { > >> + if (unlikely(__get_user(state, sd->selector))) > >> + do_exit(SIGSEGV); > >> + > >> + if (likely(state == 0)) > >> + return 0; > >> + > >> + if (state != 1) > >> + do_exit(SIGSEGV); > > > > This seems a bit extreme and hard to debug if it ever happens. > > Makes sense, but I don't see a better way to return the error here. > Maybe a SIGSYS with a different si_errno? Alternatively, we could > revert to the previous behavior of allowing syscalls on state != 0, that > existed in v1. What do you think? > I don't have a strong opinion. SIGSYS with different si_errno is probably reasonable. --Andy
Andy Lutomirski <luto@kernel.org> writes: > On Thu, Jul 16, 2020 at 12:31 PM Gabriel Krisman Bertazi > <krisman@collabora.com> wrote: > The amount of syscall entry wiring that arches need to do is IMO > already a bit out of hand. Should we instead rename TIF_SECCOMP to > TIF_SYSCALL_INTERCEPTION and have one generic callback that handles > seccomp and this new thing? The right way to go is to consolidate all the stupidly different entry/exit work handling implementations and have exactly one in generic code, i.e. what I posted a few days ago. Then we can make new features only available in the generic version by hiding the new functionality in the core code and not exposing the functions to architecture implementations. Making it easy for architectures to keep their own variant forever just proliferates the mess we have right now. Thanks, tglx
On Mon, Jul 20, 2020 at 11:23:13AM +0200, Thomas Gleixner wrote: > Andy Lutomirski <luto@kernel.org> writes: > > On Thu, Jul 16, 2020 at 12:31 PM Gabriel Krisman Bertazi > > <krisman@collabora.com> wrote: > > The amount of syscall entry wiring that arches need to do is IMO > > already a bit out of hand. Should we instead rename TIF_SECCOMP to > > TIF_SYSCALL_INTERCEPTION and have one generic callback that handles > > seccomp and this new thing? > > The right way to go is to consolidate all the stupidly different > entry/exit work handling implementations and have exactly one in generic > code, i.e. what I posted a few days ago. > > Then we can make new features only available in the generic version by > hiding the new functionality in the core code and not exposing the > functions to architecture implementations. > > Making it easy for architectures to keep their own variant forever just > proliferates the mess we have right now. Couldn't agree more. We recently added PTRACE_SYSEMU to arm64 and I deeply regret doing that now that yet another way to rewrite the syscall number has come along. I only just untangled some of the mess in our entry code for that, so I can't say I'm looking forward to opening it right back up to support this new feature. Much better to do it in the core code instead. Will
Gabriel, Gabriel Krisman Bertazi <krisman@collabora.com> writes: > Introduce a mechanism to quickly disable/enable syscall handling for a > specific process and redirect to userspace via SIGSYS. This is useful > for processes with parts that require syscall redirection and parts that > don't, but who need to perform this boundary crossing really fast, > without paying the cost of a system call to reconfigure syscall handling > on each boundary transition. This is particularly important for Windows > games running over Wine. > > The proposed interface looks like this: > > prctl(PR_SET_SYSCALL_USER_DISPATCH, <op>, <start_addr>, <end_addr>, [selector]) > > The range [<start_addr>,<end_addr>] is a part of the process memory map > that is allowed to by-pass the redirection code and dispatch syscalls > directly, such that in fast paths a process doesn't need to disable the > trap nor the kernel has to check the selector. This is essential to > return from SIGSYS to a blocked area without triggering another SIGSYS > from rt_sigreturn. Why isn't rt_sigreturn() exempt from that redirection in the first place? > --- > arch/Kconfig | 20 ++++++ > arch/x86/Kconfig | 1 + > arch/x86/entry/common.c | 5 ++ > arch/x86/include/asm/thread_info.h | 4 +- > arch/x86/kernel/signal_compat.c | 2 +- > fs/exec.c | 2 + > include/linux/sched.h | 3 + > include/linux/syscall_user_dispatch.h | 50 +++++++++++++++ > include/uapi/asm-generic/siginfo.h | 3 +- > include/uapi/linux/prctl.h | 5 ++ > kernel/Makefile | 1 + > kernel/fork.c | 1 + > kernel/sys.c | 5 ++ > kernel/syscall_user_dispatch.c | 92 +++++++++++++++++++++++++++ A big combo patch is not how we do that. Please split it up into the core part and a patch enabling it for a particular architexture. As I said in my reply to Andy, this wants to go on top of the generic entry/exit work stuff: https://lore.kernel.org/r/20200716182208.180916541@linutronix.de and then syscall_user_dispatch.c ends up in kernel/entry/ and the dispatching function is not exposed outside of that directory. I'm going to post a new version later today. Will cc you. > --- a/arch/x86/include/asm/thread_info.h > +++ b/arch/x86/include/asm/thread_info.h > @@ -93,6 +93,7 @@ struct thread_info { > #define TIF_NOTSC 16 /* TSC is not accessible in userland */ > #define TIF_IA32 17 /* IA32 compatibility process */ > #define TIF_SLD 18 /* Restore split lock detection on context switch */ > +#define TIF_SYSCALL_USER_DISPATCH 19 /* Redirect syscall for userspace handling */ There are two other things out there which compete about the last TIF bits on x86, so we need to clean that up first. > +static void trigger_sigsys(struct pt_regs *regs) > +{ > + struct kernel_siginfo info; > + > + clear_siginfo(&info); > + info.si_signo = SIGSYS; > + info.si_code = SYS_USER_DISPATCH; > + info.si_call_addr = (void __user *)KSTK_EIP(current); > + info.si_errno = 0; > + info.si_arch = syscall_get_arch(current); > + info.si_syscall = syscall_get_nr(current, regs); > + > + force_sig_info(&info); > +} > + > +int do_syscall_user_dispatch(struct pt_regs *regs) > +{ > + struct syscall_user_dispatch *sd = ¤t->syscall_dispatch; > + unsigned long ip = instruction_pointer(regs); > + char state; > + > + if (likely(ip >= sd->dispatcher_start && ip <= sd->dispatcher_end)) > + return 0; > + > + if (likely(sd->selector)) { > + if (unlikely(__get_user(state, sd->selector))) __get_user() mandates an explicit access_ok() which happened in the prctl(). So this wants a comment why there is none right here. > + do_exit(SIGSEGV); > + > + if (likely(state == 0)) > + return 0; > + > + if (state != 1) > + do_exit(SIGSEGV); If that happens its going to be quite interesting to debug. Also please use proper defines which are exposed to user space instead of 0/1. > + } > + > + syscall_rollback(current, regs); > + trigger_sigsys(regs); > + > + return 1; > +} > + > +int set_syscall_user_dispatch(int mode, unsigned long dispatcher_start, > + unsigned long dispatcher_end, char __user *selector) > +{ > + switch (mode) { > + case PR_SYS_DISPATCH_OFF: > + if (dispatcher_start || dispatcher_end || selector) > + return -EINVAL; > + break; > + case PR_SYS_DISPATCH_ON: > + /* > + * Validate the direct dispatcher region just for basic > + * sanity. If the user is able to submit a syscall from > + * an address, that address is obviously valid. > + */ > + if (dispatcher_end < dispatcher_start) > + return -EINVAL; > + > + if (selector && !access_ok(selector, 1)) sizeof(*selector) Thanks, tglx
Hi Thomas, Thanks for the valuable feedback! Thomas Gleixner <tglx@linutronix.de> writes: > Gabriel Krisman Bertazi <krisman@collabora.com> writes: >> Introduce a mechanism to quickly disable/enable syscall handling for a >> specific process and redirect to userspace via SIGSYS. This is useful >> for processes with parts that require syscall redirection and parts that >> don't, but who need to perform this boundary crossing really fast, >> without paying the cost of a system call to reconfigure syscall handling >> on each boundary transition. This is particularly important for Windows >> games running over Wine. >> >> The proposed interface looks like this: >> >> prctl(PR_SET_SYSCALL_USER_DISPATCH, <op>, <start_addr>, <end_addr>, [selector]) >> >> The range [<start_addr>,<end_addr>] is a part of the process memory map >> that is allowed to by-pass the redirection code and dispatch syscalls >> directly, such that in fast paths a process doesn't need to disable the >> trap nor the kernel has to check the selector. This is essential to >> return from SIGSYS to a blocked area without triggering another SIGSYS >> from rt_sigreturn. > > Why isn't rt_sigreturn() exempt from that redirection in the first > place? This was actually a design decision for me. The main use case I'm considering is emulation of applications written for other OSs (games over wine), which means this dispatcher code is exposed to applications built against different ABIs, who trigger syscalls with bogus parameters (from a linux perspective) In this emulation scenario, I cannot really trust the syscall number means rt_sigreturn, so I try to only base the dispatcher decision on the memory region and selector variable. I think the best we can do is what Andy said: to exempt rt_sigreturn when it comes from the vdso, for architectures that do it that way. > >> --- >> arch/Kconfig | 20 ++++++ >> arch/x86/Kconfig | 1 + >> arch/x86/entry/common.c | 5 ++ >> arch/x86/include/asm/thread_info.h | 4 +- >> arch/x86/kernel/signal_compat.c | 2 +- >> fs/exec.c | 2 + >> include/linux/sched.h | 3 + >> include/linux/syscall_user_dispatch.h | 50 +++++++++++++++ >> include/uapi/asm-generic/siginfo.h | 3 +- >> include/uapi/linux/prctl.h | 5 ++ >> kernel/Makefile | 1 + >> kernel/fork.c | 1 + >> kernel/sys.c | 5 ++ >> kernel/syscall_user_dispatch.c | 92 +++++++++++++++++++++++++++ > > A big combo patch is not how we do that. Please split it up into the > core part and a patch enabling it for a particular architexture. > > As I said in my reply to Andy, this wants to go on top of the generic > entry/exit work stuff: > > https://lore.kernel.org/r/20200716182208.180916541@linutronix.de > > and then syscall_user_dispatch.c ends up in kernel/entry/ and the > dispatching function is not exposed outside of that directory. > > I'm going to post a new version later today. Will cc you. Thanks. Will do!
On Thu, Jul 16, 2020 at 09:48:50PM -0700, Andy Lutomirski wrote: > On Thu, Jul 16, 2020 at 7:15 PM Gabriel Krisman Bertazi > <krisman@collabora.com> wrote: > > > > Andy Lutomirski <luto@kernel.org> writes: > > > > > On Thu, Jul 16, 2020 at 12:31 PM Gabriel Krisman Bertazi > > > <krisman@collabora.com> wrote: > > >> > > > > > > This is quite nice. I have a few comments, though: > > > > > > You mentioned rt_sigreturn(). Should this automatically exempt the > > > kernel-provided signal restorer on architectures (e.g. x86_32) that > > > provide one? > > > > That seems reasonable. Not sure how easy it is to do it, though. > > For better or for worse, it's currently straightforward because the code is: > > __kernel_sigreturn: > .LSTART_sigreturn: > popl %eax /* XXX does this mean it needs unwind info? */ > movl $__NR_sigreturn, %eax > SYSCALL_ENTER_KERNEL > > and SYSCALL_ENTER_KERNEL is hardwired as int $0x80. (The latter is > probably my fault, for better or for worse.) So this would change to: > > __vdso32_sigreturn_syscall: > SYSCALL_ENTER_KERNEL > > and vdso2c would wire up __vdso32_sigreturn_syscall. Then there would > be something like: > > bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs); > > and that would be that. Does anyone have an opinion as to whether > this is a good idea? Modern glibc shouldn't be using this mechanism, > I think, but I won't swear to it. On arm64 sigreturn is always through the vdso, so IIUC we'd certainly need something like this. Otherwise it'd be the user's responsibility to register the vdso sigtramp range when making the prctl, and flip the selector in each signal handler, which sounds both painful and fragile. Mark.
diff --git a/arch/Kconfig b/arch/Kconfig index 8cc35dc556c7..0ebd971d0d8f 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -465,6 +465,26 @@ config SECCOMP_FILTER See Documentation/userspace-api/seccomp_filter.rst for details. +config HAVE_ARCH_SYSCALL_USER_DISPATCH + bool + help + An arch should select this symbol if it provides all of these things: + - TIF_SYSCALL_USER_DISPATCH + - syscall_get_arch + - syscall_rollback + - syscall_get_nr + - SIGSYS siginfo_t support + +config SYSCALL_USER_DISPATCH + bool "Support syscall redirection to userspace dispatcher" + depends on HAVE_ARCH_SYSCALL_USER_DISPATCH + help + Enable tasks to ask the kernel to redirect syscalls not + issued from a predefined dispatcher back to userspace, + depending on a userspace memory selector. + + This option is useful to optimize games running over Wine. + config HAVE_ARCH_STACKLEAK bool help diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 883da0abf779..466a3a9c0708 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -149,6 +149,7 @@ config X86 select HAVE_ARCH_COMPAT_MMAP_BASES if MMU && COMPAT select HAVE_ARCH_PREL32_RELOCATIONS select HAVE_ARCH_SECCOMP_FILTER + select HAVE_ARCH_SYSCALL_USER_DISPATCH select HAVE_ARCH_THREAD_STRUCT_WHITELIST select HAVE_ARCH_STACKLEAK select HAVE_ARCH_TRACEHOOK diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index bd3f14175193..6c1360a7f260 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -138,6 +138,11 @@ static long syscall_trace_enter(struct pt_regs *regs) return -1L; } + if (work & _TIF_SYSCALL_USER_DISPATCH) { + if (do_syscall_user_dispatch(regs)) + return -1L; + } + #ifdef CONFIG_SECCOMP /* * Do seccomp after ptrace, to catch any tracer changes. diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h index 8de8ceccb8bc..b26a9f2f0491 100644 --- a/arch/x86/include/asm/thread_info.h +++ b/arch/x86/include/asm/thread_info.h @@ -93,6 +93,7 @@ struct thread_info { #define TIF_NOTSC 16 /* TSC is not accessible in userland */ #define TIF_IA32 17 /* IA32 compatibility process */ #define TIF_SLD 18 /* Restore split lock detection on context switch */ +#define TIF_SYSCALL_USER_DISPATCH 19 /* Redirect syscall for userspace handling */ #define TIF_MEMDIE 20 /* is terminating due to OOM killer */ #define TIF_POLLING_NRFLAG 21 /* idle is polling for TIF_NEED_RESCHED */ #define TIF_IO_BITMAP 22 /* uses I/O bitmap */ @@ -123,6 +124,7 @@ struct thread_info { #define _TIF_NOTSC (1 << TIF_NOTSC) #define _TIF_IA32 (1 << TIF_IA32) #define _TIF_SLD (1 << TIF_SLD) +#define _TIF_SYSCALL_USER_DISPATCH (1 << TIF_SYSCALL_USER_DISPATCH) #define _TIF_POLLING_NRFLAG (1 << TIF_POLLING_NRFLAG) #define _TIF_IO_BITMAP (1 << TIF_IO_BITMAP) #define _TIF_FORCED_TF (1 << TIF_FORCED_TF) @@ -136,7 +138,7 @@ struct thread_info { /* Work to do before invoking the actual syscall. */ #define _TIF_WORK_SYSCALL_ENTRY \ (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | _TIF_SYSCALL_AUDIT | \ - _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT) + _TIF_SECCOMP | _TIF_SYSCALL_TRACEPOINT | _TIF_SYSCALL_USER_DISPATCH) /* flags to check in __switch_to() */ #define _TIF_WORK_CTXSW_BASE \ diff --git a/arch/x86/kernel/signal_compat.c b/arch/x86/kernel/signal_compat.c index 9ccbf0576cd0..210aecc6eab9 100644 --- a/arch/x86/kernel/signal_compat.c +++ b/arch/x86/kernel/signal_compat.c @@ -31,7 +31,7 @@ static inline void signal_compat_build_tests(void) BUILD_BUG_ON(NSIGBUS != 5); BUILD_BUG_ON(NSIGTRAP != 5); BUILD_BUG_ON(NSIGCHLD != 6); - BUILD_BUG_ON(NSIGSYS != 1); + BUILD_BUG_ON(NSIGSYS != 2); /* This is part of the ABI and can never change in size: */ BUILD_BUG_ON(sizeof(compat_siginfo_t) != 128); diff --git a/fs/exec.c b/fs/exec.c index e6e8a9a70327..849f618ed790 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1386,6 +1386,8 @@ int begin_new_exec(struct linux_binprm * bprm) flush_thread(); me->personality &= ~bprm->per_clear; + clear_tsk_syscall_user_dispatch(me); + /* * We have to apply CLOEXEC before we change whether the process is * dumpable (in setup_new_exec) to avoid a race with a process in userspace diff --git a/include/linux/sched.h b/include/linux/sched.h index 692e327d7455..407b868146e1 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -32,6 +32,7 @@ #include <linux/posix-timers.h> #include <linux/rseq.h> #include <linux/kcsan.h> +#include <linux/syscall_user_dispatch.h> /* task_struct member predeclarations (sorted alphabetically): */ struct audit_context; @@ -953,6 +954,8 @@ struct task_struct { #endif struct seccomp seccomp; + struct syscall_user_dispatch syscall_dispatch; + /* Thread group tracking: */ u64 parent_exec_id; u64 self_exec_id; diff --git a/include/linux/syscall_user_dispatch.h b/include/linux/syscall_user_dispatch.h new file mode 100644 index 000000000000..a49e2de93705 --- /dev/null +++ b/include/linux/syscall_user_dispatch.h @@ -0,0 +1,50 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Copyright (C) 2020 Collabora Ltd. + */ +#ifndef _SYSCALL_USER_DISPATCH_H +#define _SYSCALL_USER_DISPATCH_H + +struct task_struct; +static void clear_tsk_thread_flag(struct task_struct *tsk, int flag); + +#ifdef CONFIG_SYSCALL_USER_DISPATCH +struct syscall_user_dispatch { + char __user *selector; + unsigned long dispatcher_start; + unsigned long dispatcher_end; +}; + +int do_syscall_user_dispatch(struct pt_regs *regs); +int set_syscall_user_dispatch(int mode, unsigned long dispatcher_start, + unsigned long dispatcher_end, + char __user *selector); + +static inline void clear_tsk_syscall_user_dispatch(struct task_struct *tsk) +{ + clear_tsk_thread_flag(tsk, TIF_SYSCALL_USER_DISPATCH); +} + +#else +struct syscall_user_dispatch {}; + +static inline int set_syscall_user_dispatch(int mode, unsigned long dispatcher_start, + unsigned long dispatcher_end, + char __user *selector) +{ + return -EINVAL; +} + +static inline int do_syscall_user_dispatch(struct pt_regs *regs) +{ + WARN_ON_ONCE(1); + return 0; +} + +static inline void clear_tsk_syscall_user_dispatch(struct task_struct *tsk) +{ +} + +#endif /* CONFIG_SYSCALL_USER_DISPATCH */ + +#endif /* _SYSCALL_USER_DISPATCH_H */ diff --git a/include/uapi/asm-generic/siginfo.h b/include/uapi/asm-generic/siginfo.h index cb3d6c267181..37741908b846 100644 --- a/include/uapi/asm-generic/siginfo.h +++ b/include/uapi/asm-generic/siginfo.h @@ -284,7 +284,8 @@ typedef struct siginfo { * SIGSYS si_codes */ #define SYS_SECCOMP 1 /* seccomp triggered */ -#define NSIGSYS 1 +#define SYS_USER_DISPATCH 2 /* syscall user dispatch triggered */ +#define NSIGSYS 2 /* * SIGEMT si_codes diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index 07b4f8131e36..96265246383d 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -238,4 +238,9 @@ struct prctl_mm_map { #define PR_SET_IO_FLUSHER 57 #define PR_GET_IO_FLUSHER 58 +/* Dispatch syscalls to a userspace handler */ +#define PR_SET_SYSCALL_USER_DISPATCH 59 +# define PR_SYS_DISPATCH_OFF 0 +# define PR_SYS_DISPATCH_ON 1 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/Makefile b/kernel/Makefile index f3218bc5ec69..158b8c61592f 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -92,6 +92,7 @@ obj-$(CONFIG_DETECT_HUNG_TASK) += hung_task.o obj-$(CONFIG_LOCKUP_DETECTOR) += watchdog.o obj-$(CONFIG_HARDLOCKUP_DETECTOR_PERF) += watchdog_hld.o obj-$(CONFIG_SECCOMP) += seccomp.o +obj-$(CONFIG_SYSCALL_USER_DISPATCH) += syscall_user_dispatch.o obj-$(CONFIG_RELAY) += relay.o obj-$(CONFIG_SYSCTL) += utsname_sysctl.o obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o diff --git a/kernel/fork.c b/kernel/fork.c index 142b23645d82..c6b64a849fec 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -921,6 +921,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node) clear_user_return_notifier(tsk); clear_tsk_need_resched(tsk); set_task_stack_end_magic(tsk); + clear_tsk_syscall_user_dispatch(tsk); #ifdef CONFIG_STACKPROTECTOR tsk->stack_canary = get_random_canary(); diff --git a/kernel/sys.c b/kernel/sys.c index 00a96746e28a..d85880873c92 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -42,6 +42,7 @@ #include <linux/syscore_ops.h> #include <linux/version.h> #include <linux/ctype.h> +#include <linux/syscall_user_dispatch.h> #include <linux/compat.h> #include <linux/syscalls.h> @@ -2527,6 +2528,10 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, error = (current->flags & PR_IO_FLUSHER) == PR_IO_FLUSHER; break; + case PR_SET_SYSCALL_USER_DISPATCH: + error = set_syscall_user_dispatch((int) arg2, arg3, arg4, + (char __user *) arg5); + break; default: error = -EINVAL; break; diff --git a/kernel/syscall_user_dispatch.c b/kernel/syscall_user_dispatch.c new file mode 100644 index 000000000000..39ee29c2b91f --- /dev/null +++ b/kernel/syscall_user_dispatch.c @@ -0,0 +1,92 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2020 Collabora Ltd. + */ +#include <linux/sched.h> +#include <linux/prctl.h> +#include <linux/syscall_user_dispatch.h> +#include <linux/uaccess.h> +#include <linux/signal.h> + +#include <asm/syscall.h> + +#include <linux/sched/signal.h> +#include <linux/sched/task_stack.h> + +static void trigger_sigsys(struct pt_regs *regs) +{ + struct kernel_siginfo info; + + clear_siginfo(&info); + info.si_signo = SIGSYS; + info.si_code = SYS_USER_DISPATCH; + info.si_call_addr = (void __user *)KSTK_EIP(current); + info.si_errno = 0; + info.si_arch = syscall_get_arch(current); + info.si_syscall = syscall_get_nr(current, regs); + + force_sig_info(&info); +} + +int do_syscall_user_dispatch(struct pt_regs *regs) +{ + struct syscall_user_dispatch *sd = ¤t->syscall_dispatch; + unsigned long ip = instruction_pointer(regs); + char state; + + if (likely(ip >= sd->dispatcher_start && ip <= sd->dispatcher_end)) + return 0; + + if (likely(sd->selector)) { + if (unlikely(__get_user(state, sd->selector))) + do_exit(SIGSEGV); + + if (likely(state == 0)) + return 0; + + if (state != 1) + do_exit(SIGSEGV); + } + + syscall_rollback(current, regs); + trigger_sigsys(regs); + + return 1; +} + +int set_syscall_user_dispatch(int mode, unsigned long dispatcher_start, + unsigned long dispatcher_end, char __user *selector) +{ + switch (mode) { + case PR_SYS_DISPATCH_OFF: + if (dispatcher_start || dispatcher_end || selector) + return -EINVAL; + break; + case PR_SYS_DISPATCH_ON: + /* + * Validate the direct dispatcher region just for basic + * sanity. If the user is able to submit a syscall from + * an address, that address is obviously valid. + */ + if (dispatcher_end < dispatcher_start) + return -EINVAL; + + if (selector && !access_ok(selector, 1)) + return -EFAULT; + + break; + default: + return -EINVAL; + } + + current->syscall_dispatch.selector = selector; + current->syscall_dispatch.dispatcher_start = dispatcher_start; + current->syscall_dispatch.dispatcher_end = dispatcher_end; + + if (mode == PR_SYS_DISPATCH_ON) + set_tsk_thread_flag(current, TIF_SYSCALL_USER_DISPATCH); + else + clear_tsk_thread_flag(current, TIF_SYSCALL_USER_DISPATCH); + + return 0; +}