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![Elvira Khabirova](/assets/img/avatar_default.png)
PTRACE_GET_SYSCALL_INFO is a generic ptrace API that lets ptracer obtain
details of the syscall the tracee is blocked in.
There are two reasons for a special syscall-related ptrace request.
Firstly, with the current ptrace API there are cases when ptracer cannot
retrieve necessary information about syscalls. Some examples include:
* The notorious int-0x80-from-64-bit-task issue. See [1] for details.
In short, if a 64-bit task performs a syscall through int 0x80, its
tracer has no reliable means to find out that the syscall was, in
fact, a compat syscall, and misidentifies it.
* Syscall-enter-stop and syscall-exit-stop look the same for the
tracer. Common practice is to keep track of the sequence of
ptrace-stops in order not to mix the two syscall-stops up. But it is
not as simple as it looks; for example, strace had a (just recently
fixed) long-standing bug where attaching strace to a tracee that is
performing the execve system call led to the tracer identifying the
following syscall-exit-stop as syscall-enter-stop, which messed up
all the state tracking.
* Since the introduction of commit 84d77d3f06
("ptrace: Don't allow
accessing an undumpable mm"), both PTRACE_PEEKDATA and
process_vm_readv become unavailable when the process dumpable flag is
cleared. On such architectures as ia64 this results in all syscall
arguments being unavailable for the tracer.
Secondly, ptracers also have to support a lot of arch-specific code for
obtaining information about the tracee. For some architectures, this
requires a ptrace(PTRACE_PEEKUSER, ...) invocation for every syscall
argument and return value.
ptrace(2) man page:
long ptrace(enum __ptrace_request request, pid_t pid,
void *addr, void *data);
...
PTRACE_GET_SYSCALL_INFO
Retrieve information about the syscall that caused the stop.
The information is placed into the buffer pointed by "data"
argument, which should be a pointer to a buffer of type
"struct ptrace_syscall_info".
The "addr" argument contains the size of the buffer pointed to
by "data" argument (i.e., sizeof(struct ptrace_syscall_info)).
The return value contains the number of bytes available
to be written by the kernel.
If the size of data to be written by the kernel exceeds the size
specified by "addr" argument, the output is truncated.
[ldv@altlinux.org: selftests/seccomp/seccomp_bpf: update for PTRACE_GET_SYSCALL_INFO]
Link: http://lkml.kernel.org/r/20190708182904.GA12332@altlinux.org
Link: http://lkml.kernel.org/r/20190510152842.GF28558@altlinux.org
Signed-off-by: Elvira Khabirova <lineprinter@altlinux.org>
Co-developed-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: Eugene Syromyatnikov <esyr@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Greentime Hu <greentime@andestech.com>
Cc: Helge Deller <deller@gmx.de> [parisc]
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: kbuild test robot <lkp@intel.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Richard Kuo <rkuo@codeaurora.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vincent Chen <deanbo422@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
201 lines
7.3 KiB
C
201 lines
7.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0-only */
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/*
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* Tracing hooks
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*
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* Copyright (C) 2008-2009 Red Hat, Inc. All rights reserved.
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*
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* This file defines hook entry points called by core code where
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* user tracing/debugging support might need to do something. These
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* entry points are called tracehook_*(). Each hook declared below
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* has a detailed kerneldoc comment giving the context (locking et
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* al) from which it is called, and the meaning of its return value.
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*
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* Each function here typically has only one call site, so it is ok
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* to have some nontrivial tracehook_*() inlines. In all cases, the
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* fast path when no tracing is enabled should be very short.
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*
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* The purpose of this file and the tracehook_* layer is to consolidate
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* the interface that the kernel core and arch code uses to enable any
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* user debugging or tracing facility (such as ptrace). The interfaces
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* here are carefully documented so that maintainers of core and arch
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* code do not need to think about the implementation details of the
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* tracing facilities. Likewise, maintainers of the tracing code do not
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* need to understand all the calling core or arch code in detail, just
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* documented circumstances of each call, such as locking conditions.
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*
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* If the calling core code changes so that locking is different, then
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* it is ok to change the interface documented here. The maintainer of
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* core code changing should notify the maintainers of the tracing code
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* that they need to work out the change.
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*
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* Some tracehook_*() inlines take arguments that the current tracing
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* implementations might not necessarily use. These function signatures
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* are chosen to pass in all the information that is on hand in the
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* caller and might conceivably be relevant to a tracer, so that the
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* core code won't have to be updated when tracing adds more features.
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* If a call site changes so that some of those parameters are no longer
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* already on hand without extra work, then the tracehook_* interface
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* can change so there is no make-work burden on the core code. The
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* maintainer of core code changing should notify the maintainers of the
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* tracing code that they need to work out the change.
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*/
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#ifndef _LINUX_TRACEHOOK_H
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#define _LINUX_TRACEHOOK_H 1
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#include <linux/sched.h>
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#include <linux/ptrace.h>
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#include <linux/security.h>
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#include <linux/task_work.h>
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#include <linux/memcontrol.h>
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#include <linux/blk-cgroup.h>
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struct linux_binprm;
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/*
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* ptrace report for syscall entry and exit looks identical.
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*/
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static inline int ptrace_report_syscall(struct pt_regs *regs,
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unsigned long message)
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{
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int ptrace = current->ptrace;
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if (!(ptrace & PT_PTRACED))
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return 0;
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current->ptrace_message = message;
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ptrace_notify(SIGTRAP | ((ptrace & PT_TRACESYSGOOD) ? 0x80 : 0));
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/*
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* this isn't the same as continuing with a signal, but it will do
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* for normal use. strace only continues with a signal if the
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* stopping signal is not SIGTRAP. -brl
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*/
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if (current->exit_code) {
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send_sig(current->exit_code, current, 1);
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current->exit_code = 0;
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}
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current->ptrace_message = 0;
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return fatal_signal_pending(current);
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}
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/**
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* tracehook_report_syscall_entry - task is about to attempt a system call
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* @regs: user register state of current task
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*
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* This will be called if %TIF_SYSCALL_TRACE or %TIF_SYSCALL_EMU have been set,
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* when the current task has just entered the kernel for a system call.
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* Full user register state is available here. Changing the values
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* in @regs can affect the system call number and arguments to be tried.
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* It is safe to block here, preventing the system call from beginning.
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*
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* Returns zero normally, or nonzero if the calling arch code should abort
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* the system call. That must prevent normal entry so no system call is
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* made. If @task ever returns to user mode after this, its register state
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* is unspecified, but should be something harmless like an %ENOSYS error
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* return. It should preserve enough information so that syscall_rollback()
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* can work (see asm-generic/syscall.h).
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*
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* Called without locks, just after entering kernel mode.
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*/
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static inline __must_check int tracehook_report_syscall_entry(
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struct pt_regs *regs)
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{
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return ptrace_report_syscall(regs, PTRACE_EVENTMSG_SYSCALL_ENTRY);
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}
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/**
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* tracehook_report_syscall_exit - task has just finished a system call
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* @regs: user register state of current task
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* @step: nonzero if simulating single-step or block-step
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*
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* This will be called if %TIF_SYSCALL_TRACE has been set, when the
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* current task has just finished an attempted system call. Full
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* user register state is available here. It is safe to block here,
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* preventing signals from being processed.
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*
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* If @step is nonzero, this report is also in lieu of the normal
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* trap that would follow the system call instruction because
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* user_enable_block_step() or user_enable_single_step() was used.
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* In this case, %TIF_SYSCALL_TRACE might not be set.
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*
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* Called without locks, just before checking for pending signals.
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*/
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static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
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{
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if (step)
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user_single_step_report(regs);
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else
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ptrace_report_syscall(regs, PTRACE_EVENTMSG_SYSCALL_EXIT);
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}
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/**
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* tracehook_signal_handler - signal handler setup is complete
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* @stepping: nonzero if debugger single-step or block-step in use
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*
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* Called by the arch code after a signal handler has been set up.
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* Register and stack state reflects the user handler about to run.
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* Signal mask changes have already been made.
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*
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* Called without locks, shortly before returning to user mode
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* (or handling more signals).
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*/
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static inline void tracehook_signal_handler(int stepping)
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{
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if (stepping)
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ptrace_notify(SIGTRAP);
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}
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/**
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* set_notify_resume - cause tracehook_notify_resume() to be called
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* @task: task that will call tracehook_notify_resume()
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*
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* Calling this arranges that @task will call tracehook_notify_resume()
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* before returning to user mode. If it's already running in user mode,
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* it will enter the kernel and call tracehook_notify_resume() soon.
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* If it's blocked, it will not be woken.
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*/
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static inline void set_notify_resume(struct task_struct *task)
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{
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#ifdef TIF_NOTIFY_RESUME
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if (!test_and_set_tsk_thread_flag(task, TIF_NOTIFY_RESUME))
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kick_process(task);
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#endif
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}
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/**
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* tracehook_notify_resume - report when about to return to user mode
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* @regs: user-mode registers of @current task
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*
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* This is called when %TIF_NOTIFY_RESUME has been set. Now we are
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* about to return to user mode, and the user state in @regs can be
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* inspected or adjusted. The caller in arch code has cleared
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* %TIF_NOTIFY_RESUME before the call. If the flag gets set again
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* asynchronously, this will be called again before we return to
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* user mode.
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*
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* Called without locks.
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*/
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static inline void tracehook_notify_resume(struct pt_regs *regs)
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{
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/*
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* The caller just cleared TIF_NOTIFY_RESUME. This barrier
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* pairs with task_work_add()->set_notify_resume() after
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* hlist_add_head(task->task_works);
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*/
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smp_mb__after_atomic();
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if (unlikely(current->task_works))
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task_work_run();
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#ifdef CONFIG_KEYS_REQUEST_CACHE
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if (unlikely(current->cached_requested_key)) {
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key_put(current->cached_requested_key);
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current->cached_requested_key = NULL;
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}
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#endif
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mem_cgroup_handle_over_high();
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blkcg_maybe_throttle_current();
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}
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#endif /* <linux/tracehook.h> */
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