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From: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Shuah Khan <shuah@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org,
	Andy Lutomirski <luto@amacapital.net>,
	Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Changbin Du <changbin.du@gmail.com>, Jann Horn <jannh@google.com>,
	Kees Cook <keescook@chromium.org>,
	Andy Lutomirski <luto@kernel.org>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	Nadav Amit <namit@vmware.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	yhs@fb.com
Subject: Re: [RFC PATCH v6 1/6] x86/uaccess: Allow access_ok() in irq context if pagefault_disabled
Date: Mon, 6 May 2019 11:39:23 -0400	[thread overview]
Message-ID: <20190506113923.4fbd56ae@gandalf.local.home> (raw)
In-Reply-To: <20190507002203.1db020838c07a12bec87ca73@kernel.org>

On Tue, 7 May 2019 00:22:03 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Hi Steve,
> 
> It seems I missed this message...

No problem. The number of times I missed messages... ugh.

> 
> > 
> > I'm curious, what interrupt handler are kprobes executing in that needs
> > random user space addresses?  
> 
> Sorry for confusion. Kprobes is using an exception (of course!). So the
> title can mislead, it should be "in exception" instead of "in irq context",
> However, current code checks it by "!in_task()", which includes both of
> IRQ and exception. A better solution might change it to "in_irq()".

That makes sense.

> 
> However, I could not find a way to distinguish the "exception" and
> "external IRQ" by the execution context (based on the preempt count)
> because exception is treated as a kind of IRQ.
> Thus, in this patch, I changed it as not only checking what the context
> is, but also whether it is appropriately called.
> 

As exceptions typically disable interrupts, we treat them as their own
context. Especially for looking at recursion detection algorithms,
which allow for different contexts to recurse.

Normal-context -> softirq -> exception / IRQ -> NMI


Anyway, that WARN_ON_IN_IRQ() should come with a big comment about why
we allow it if we have pagefault_disable() set.

This will need to go through the x86 maintainers. I'll go and review
the tracing patches of this series and give an ack / reviewed-by if
there's no issues.

-- Steve

  reply	other threads:[~2019-05-06 15:39 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-18  6:42 [RFC PATCH v6 0/6] tracing/probes: uaccess: Add support user-space access Masami Hiramatsu
2019-03-18  6:43 ` [RFC PATCH v6 1/6] x86/uaccess: Allow access_ok() in irq context if pagefault_disabled Masami Hiramatsu
2019-03-22  2:46   ` Steven Rostedt
2019-05-06 15:22     ` Masami Hiramatsu
2019-05-06 15:39       ` Steven Rostedt [this message]
2019-03-18  6:43 ` [RFC PATCH v6 2/6] uaccess: Add non-pagefault user-space read functions Masami Hiramatsu
2019-03-18  6:43 ` [RFC PATCH v6 3/6] tracing/probe: Add ustring type for user-space string Masami Hiramatsu
2019-03-18  6:43 ` [RFC PATCH v6 4/6] tracing/probe: Support user-space dereference Masami Hiramatsu
2019-05-06 15:52   ` Steven Rostedt
2019-05-08  4:11     ` Masami Hiramatsu
2019-05-08 15:22       ` Steven Rostedt
2019-05-13 12:11         ` Masami Hiramatsu
2019-03-18  6:44 ` [RFC PATCH v6 5/6] selftests/ftrace: Add user-memory access syntax testcase Masami Hiramatsu
2019-03-18  6:44 ` [RFC PATCH v6 6/6] perf-probe: Add user memory access attribute support Masami Hiramatsu

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