Messages in this thread Patch in this message | | | Date | Wed, 4 Apr 2018 13:13:10 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v2] tracing, printk: Force no hashing when trace_printk() is used |
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On Wed, 4 Apr 2018 11:34:55 +0900 Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:
> On (04/03/18 18:03), Steven Rostedt wrote: > > > > > he'd want you to change all the trace_printk()s to %px with > > > justifications, though. > > > > What trace_printk()s do you want to change? They are throw away > > functions. trace_printk() is not something that stays in the kernel. > > It's added during debugging and then removed before submitting what you > > are working on upstream. > > Seems that your patch also can fix up bpf_trace_printk() - it doesn't > even support %px, only hashed %p, which it passes to __trace_printk(). >
Crap, that should not work, but it does. I need to update the code to prevent that from happening. I don't want any user space code to be able to enable this.
Something like this will even prevent modules from disabling the printk hash...
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 2a1d01666dd2..c4af083742b0 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2834,6 +2834,14 @@ static int alloc_percpu_trace_buffer(void) static int buffers_allocated; +/* Will become read only after boot */ +static const bool disable_printk_hash; + +static void set_printk_hash(bool val) +{ + *(bool *)&disable_printk_hash = val; +} + void trace_printk_init_buffers(void) { if (buffers_allocated) @@ -2864,9 +2872,11 @@ void trace_printk_init_buffers(void) buffers_allocated = 1; - /* This is a debug kernel, allow pointers to be shown */ - static_branch_enable(&trace_debug); - kptr_restrict = 0; + if (disable_printk_hash) { + /* This is a debug kernel, allow pointers to be shown */ + static_branch_enable(&trace_debug); + kptr_restrict = 0; + } /* * trace_printk_init_buffers() can be called by modules. @@ -8456,10 +8466,13 @@ __init static int tracer_alloc_buffers(void) if (!alloc_cpumask_var(&global_trace.tracing_cpumask, GFP_KERNEL)) goto out_free_buffer_mask; + /* Only trace_printk() in the core kernel can disable hashing */ + set_printk_hash(true); /* Only allocate trace_printk buffers if a trace_printk exists */ if (__stop___trace_bprintk_fmt != __start___trace_bprintk_fmt) /* Must be called before global_trace.buffer is allocated */ trace_printk_init_buffers(); + set_printk_hash(false); /* To save memory, keep the ring buffer size to its minimum */ if (ring_buffer_expanded)
-- Steve
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