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Message-ID: <da4beb18-7bed-41bd-aeba-94497eff0b58@efficios.com>
Date: Sat, 26 Oct 2024 11:17:38 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: Jordan Rife <jrife@...gle.com>, acme@...nel.org,
alexander.shishkin@...ux.intel.com, andrii.nakryiko@...il.com,
ast@...nel.org, bpf@...r.kernel.org, joel@...lfernandes.org,
linux-kernel@...r.kernel.org, mark.rutland@....com, mhiramat@...nel.org,
mingo@...hat.com, mjeanson@...icios.com, namhyung@...nel.org,
paulmck@...nel.org, peterz@...radead.org,
syzbot+b390c8062d8387b6272a@...kaller.appspotmail.com, yhs@...com
Subject: Re: [RFC PATCH v1] tracing: Fix syscall tracepoint use-after-free
On 2024-10-26 10:25, Mathieu Desnoyers wrote:
> On 2024-10-26 03:13, Steven Rostedt wrote:
>> On Fri, 25 Oct 2024 15:38:48 -0400
>> Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
>>
>>>> I'm curious if it might be better to add some field to struct
>>>> tracepoint like "sleepable" rather than adding a special case here
>>>> based on the name? Of course, if it's only ever going to be these
>>>> two cases then maybe adding a new field doesn't make sense.
>>>
>>> I know Steven is reluctant to bloat the tracepoint struct because there
>>> are lots of tracepoint instances (thousands). So for now I thought that
>>> just comparing the name would be a good start.
>>
>> You are correct. I really trying to keep the footprint of
>> tracepoints/events down.
>>
>>>
>>> We can eventually go a different route as well: introduce a section just
>>> to put the syscall tracepoints, and compare the struct tracepoint
>>> pointers to the section begin/end range. But it's rather complex
>>> for what should remain a simple fix.
>>
>> A separate section could work.
>
> I have another approach to suggest: it shrinks the
> size of struct tracepoint from 80 bytes down to 72 bytes
> on x86-64, we don't have to do any section/linker
> script trickery, and it's extensible for future flags:
>
> struct static_key {
> int enabled;
> void *p;
> };
>
> struct static_key_false {
> struct static_key key;
> };
>
> struct static_call_key {
> void *func;
> void *p;
> };
>
> struct tracepoint {
> const char *name; /* Tracepoint name */
> struct static_key_false key;
> struct static_call_key *static_call_key;
> void *static_call_tramp;
> void *iterator;
> void *probestub;
> void *funcs;
> /* Flags. */
> unsigned int regfunc:1,
> syscall:1;
> };
>
> struct tracepoint_regfunc {
> struct tracepoint tp;
> int (*regfunc)(void);
> void (*unregfunc)(void);
> };
>
> Basically, a tracepoint with regfunc would define a
> struct tracepoint_regfunc rather than a struct tracepoint.
> So we remove both regfunc and unregfunc NULL pointers in
> the common case, which gives us plenty of room for flags.
>
> When we want to access the regfunc/unregfunc from
> a struct tracepoint, we check the regfunc flag, and
> if set, we can use container_of() to get the struct
> tracepoint_regfunc.
Actually I can achieve the same space saving with fewer
changes like this:
struct tracepoint_ext {
void *regfunc;
void *unregfunc;
/* Flags. */
unsigned int syscall:1;
}
struct tracepoint {
const char *name; /* Tracepoint name */
struct static_key_false key;
struct static_call_key *static_call_key;
void *static_call_tramp;
void *iterator;
void *probestub;
void *funcs;
struct tracepoint_ext *ext;
};
Thanks,
Mathieu
>
> Thoughts ?
>
> Thanks,
>
> Mathieu
>
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
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