Messages in this thread | | | From | Masami Hiramatsu <> | Subject | [RFC PATCH v6 0/6] tracing/probes: uaccess: Add support user-space access | Date | Mon, 18 Mar 2019 15:42:55 +0900 |
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Hi,
Here is the v6 series of probe-event to support user-space access.
In this version, I replaced user_access_ok() patch with access_ok() enhancement, which allows user to call access_ok() in IRQ context if it disables pagefault. In the result of this change, I also removed user_access_ok() related patch. This version also extends perf-probe to handle user-space memory. This is still not automated yet, but it can be done when __user is encoded in debuginfo.
Changes in v6: - [1/6]: (New) allow access_ok() in IRQ context if pagefault is disabled. - [3/6]: Remove user_access_ok() - [5/6]: Add $argN availablity check - [6/6]: (New) extend perf-probe to handle "@user" attribute which allows user to specify "user-space local variable"
V5 series is here;
https://lkml.kernel.org/r/155136974478.2968.3105123100519786079.stgit@devbox
In summary, strncpy_from_user() should work as below
- strncpy_from_user() can access user memory with set_fs(USER_DS) in task context
- strncpy_from_user() can access kernel memory with set_fs(KERNEL_DS) in task context (e.g. devtmpfsd and init)
- strncpy_from_user() can access user/kernel memory (depends on DS) in IRQ context if pagefault is disabled. (both verified)
PeterZ, would you still have any concern about this check?
==== Kprobe event user-space memory access features:
For user-space access extension, this series adds 2 features, "ustring" type and user-space dereference syntax. "ustring" is used for recording a null-terminated string in user-space from kprobe events.
"ustring" type is easy, it is able to use instead of "string" type, so if you want to record a user-space string via "__user char *", you can use ustring type instead of string. For example,
echo 'p do_sys_open path=+0($arg2):ustring' >> kprobe_events
will record the path string from user-space.
The user-space dereference syntax is also simple. Thi just adds 'u' prefix before an offset value.
+|-u<OFFSET>(<FETCHARG>)
e.g. +u8(%ax), +u0(+0(%si))
This is more generic. If you want to refer the variable in user- space from its address or access a field in data structure in user-space, you need to use this.
For example, if you probe do_sched_setscheduler(pid, policy, param) and record param->sched_priority, you can add new probe as below; p do_sched_setscheduler priority=+u0($arg3)
Actually, with this feature, "ustring" type is not absolutely necessary, because these are same meanings.
+0($arg2):ustring == +u0($arg2):string
Note that kprobe event provides these methods, but it doesn't change it from kernel to user automatically because we do not know whether the given address is in userspace or kernel on some arch.
Thank you,
---
Masami Hiramatsu (6): x86/uaccess: Allow access_ok() in irq context if pagefault_disabled uaccess: Add non-pagefault user-space read functions tracing/probe: Add ustring type for user-space string tracing/probe: Support user-space dereference selftests/ftrace: Add user-memory access syntax testcase perf-probe: Add user memory access attribute support
Documentation/trace/kprobetrace.rst | 28 ++++- Documentation/trace/uprobetracer.rst | 9 +- arch/x86/include/asm/uaccess.h | 4 + include/linux/uaccess.h | 19 +++ kernel/trace/trace.c | 7 + kernel/trace/trace_kprobe.c | 35 ++++++ kernel/trace/trace_probe.c | 37 +++++- kernel/trace/trace_probe.h | 3 + kernel/trace/trace_probe_tmpl.h | 37 +++++- kernel/trace/trace_uprobe.c | 19 +++ mm/maccess.c | 117 +++++++++++++++++++- tools/perf/Documentation/perf-probe.txt | 3 - tools/perf/util/probe-event.c | 11 ++ tools/perf/util/probe-event.h | 2 tools/perf/util/probe-file.c | 7 + tools/perf/util/probe-file.h | 1 tools/perf/util/probe-finder.c | 19 ++- .../ftrace/test.d/kprobe/kprobe_args_user.tc | 32 +++++ 18 files changed, 349 insertions(+), 41 deletions(-) create mode 100644 tools/testing/selftests/ftrace/test.d/kprobe/kprobe_args_user.tc
-- Masami Hiramatsu (Linaro) <mhiramat@kernel.org>
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