From: torvalds at linux-foundation.org (Linus Torvalds)
Subject: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions
Date: Fri, 3 May 2019 16:07:59 -0700 [thread overview]
Message-ID: <CAHk-=wh2vPLvsGBi6JtmEYeqHxB5UpTzHDjY5JsWG=YR0Lypzw@mail.gmail.com> (raw)
In-Reply-To: <20190503184919.2b7ef242@gandalf.local.home>
On Fri, May 3, 2019 at 3:49 PM Steven Rostedt <rostedt at goodmis.org> wrote:
>
> You are saying that we have a do_int3() for user space int3, and
> do_kernel_int3() for kernel space. That would need to be done in asm
> for both, because having x86_64 call do_int3() for kernel and
> user would be interesting.
The clean/simple way is to just do this
- x86-32 does the special asm for the kernel_do_int3(), case and
calls user_do_int3 otherwise.
- x86-64 doesn't care, and just calls "do_int3()".
We have a trivial helper function like
dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
{
if (user_mode(regs))
user_int3(regs);
else
WARN_ON_ONCE(kernel_int3(regs) != regs);
}
which adds that warning just for debug purposes.
Then we make the rule be that user_int3() does the normal stuff, and
kernel_int3() returns the pt_regs it was passed in.
Easy-peasy, there is absolutely no difference between x86-64 and
x86-32 here except for the trivial case that x86-32 does its thing at
the asm layer, which is what allows "kernel_int3()" to move pt_regs
around by a small amount.
Now, the _real_ difference is when you do the "call_emulate()" case,
which will have to do something like this
static struct pt_regs *emulate_call(struct pt_regs *regs, unsigned
long return, unsigned long target)
{
#ifdef CONFIG_X86_32
/* BIG comment about how we need to move pt_regs to make
room and to update the return 'sp' */
struct pt_regs *new = (void *)regs - 4;
unsigned long *sp = (unsigned long *)(new + 1);
memmove(new, regs, sizeof(*regs));
regs = new;
#else
unsigned long *sp = regs->sp;
regs->sp -= 4;
#endif
*sp = value;
regs->ip = target;
return regs;
}
but look, the above isn't that complicated, is it? And notice how the
subtle pt_regs movement is exactly where it needs to be and nowhere
else.
And what's the cost of all of this? NOTHING. The x86-32 entry code has
to do the test for kernel space anyway, and *all* it does now is to
call "kernel_int3" for the kernel case after having made a bit of
extra room on the stack so that you *can* move pt_regs around (maybe
people want to pop things too? It would work as well).
See what I mean by "localized to the cases the need it"?
Linus
WARNING: multiple messages have this Message-ID (diff)
From: torvalds@linux-foundation.org (Linus Torvalds)
Subject: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions
Date: Fri, 3 May 2019 16:07:59 -0700 [thread overview]
Message-ID: <CAHk-=wh2vPLvsGBi6JtmEYeqHxB5UpTzHDjY5JsWG=YR0Lypzw@mail.gmail.com> (raw)
Message-ID: <20190503230759.drGK-PAsE5mXoGF4Kgfd0MqNzTr7t2gW2Sea-vuu4F0@z> (raw)
In-Reply-To: <20190503184919.2b7ef242@gandalf.local.home>
On Fri, May 3, 2019@3:49 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> You are saying that we have a do_int3() for user space int3, and
> do_kernel_int3() for kernel space. That would need to be done in asm
> for both, because having x86_64 call do_int3() for kernel and
> user would be interesting.
The clean/simple way is to just do this
- x86-32 does the special asm for the kernel_do_int3(), case and
calls user_do_int3 otherwise.
- x86-64 doesn't care, and just calls "do_int3()".
We have a trivial helper function like
dotraplinkage void notrace do_int3(struct pt_regs *regs, long error_code)
{
if (user_mode(regs))
user_int3(regs);
else
WARN_ON_ONCE(kernel_int3(regs) != regs);
}
which adds that warning just for debug purposes.
Then we make the rule be that user_int3() does the normal stuff, and
kernel_int3() returns the pt_regs it was passed in.
Easy-peasy, there is absolutely no difference between x86-64 and
x86-32 here except for the trivial case that x86-32 does its thing at
the asm layer, which is what allows "kernel_int3()" to move pt_regs
around by a small amount.
Now, the _real_ difference is when you do the "call_emulate()" case,
which will have to do something like this
static struct pt_regs *emulate_call(struct pt_regs *regs, unsigned
long return, unsigned long target)
{
#ifdef CONFIG_X86_32
/* BIG comment about how we need to move pt_regs to make
room and to update the return 'sp' */
struct pt_regs *new = (void *)regs - 4;
unsigned long *sp = (unsigned long *)(new + 1);
memmove(new, regs, sizeof(*regs));
regs = new;
#else
unsigned long *sp = regs->sp;
regs->sp -= 4;
#endif
*sp = value;
regs->ip = target;
return regs;
}
but look, the above isn't that complicated, is it? And notice how the
subtle pt_regs movement is exactly where it needs to be and nowhere
else.
And what's the cost of all of this? NOTHING. The x86-32 entry code has
to do the test for kernel space anyway, and *all* it does now is to
call "kernel_int3" for the kernel case after having made a bit of
extra room on the stack so that you *can* move pt_regs around (maybe
people want to pop things too? It would work as well).
See what I mean by "localized to the cases the need it"?
Linus
next prev parent reply other threads:[~2019-05-03 23:07 UTC|newest]
Thread overview: 204+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190501202830.347656894@goodmis.org>
2019-05-01 20:28 ` [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions rostedt
2019-05-01 20:28 ` Steven Rostedt
2019-05-02 3:24 ` rostedt
2019-05-02 3:24 ` Steven Rostedt
2019-05-02 16:21 ` peterz
2019-05-02 16:21 ` Peter Zijlstra
2019-05-02 16:29 ` peterz
2019-05-02 16:29 ` Peter Zijlstra
2019-05-02 18:02 ` torvalds
2019-05-02 18:02 ` Linus Torvalds
2019-05-02 18:18 ` peterz
2019-05-02 18:18 ` Peter Zijlstra
2019-05-02 18:30 ` peterz
2019-05-02 18:30 ` Peter Zijlstra
2019-05-02 18:43 ` torvalds
2019-05-02 18:43 ` Linus Torvalds
2019-05-02 19:28 ` jikos
2019-05-02 19:28 ` Jiri Kosina
2019-05-02 20:25 ` luto
2019-05-02 20:25 ` Andy Lutomirski
2019-05-02 20:21 ` peterz
2019-05-02 20:21 ` Peter Zijlstra
2019-05-02 20:49 ` torvalds
2019-05-02 20:49 ` Linus Torvalds
2019-05-02 21:32 ` peterz
2019-05-02 21:32 ` Peter Zijlstra
2019-05-03 19:24 ` rostedt
2019-05-03 19:24 ` Steven Rostedt
2019-05-03 21:46 ` torvalds
2019-05-03 21:46 ` Linus Torvalds
2019-05-03 22:49 ` rostedt
2019-05-03 22:49 ` Steven Rostedt
2019-05-03 23:07 ` torvalds [this message]
2019-05-03 23:07 ` Linus Torvalds
2019-05-04 4:17 ` rostedt
2019-05-04 4:17 ` Steven Rostedt
[not found] ` <CAHk-=wiuSFbv_rELND-BLWcP0GSZ0yF=xOAEcf61GE3bU9d=yg@mail.gmail.com>
2019-05-04 18:59 ` torvalds
2019-05-04 18:59 ` Linus Torvalds
2019-05-04 20:12 ` luto
2019-05-04 20:12 ` Andy Lutomirski
2019-05-04 20:28 ` torvalds
2019-05-04 20:28 ` Linus Torvalds
2019-05-04 20:36 ` torvalds
2019-05-04 20:36 ` Linus Torvalds
2019-05-03 22:55 ` luto
2019-05-03 22:55 ` Andy Lutomirski
2019-05-03 23:16 ` torvalds
2019-05-03 23:16 ` Linus Torvalds
2019-05-03 23:32 ` luto
2019-05-03 23:32 ` Andy Lutomirski
2019-05-02 22:52 ` rostedt
2019-05-02 22:52 ` Steven Rostedt
2019-05-02 23:31 ` rostedt
2019-05-02 23:31 ` Steven Rostedt
2019-05-02 23:50 ` rostedt
2019-05-02 23:50 ` Steven Rostedt
2019-05-03 1:51 ` [RFC][PATCH 1/2 v2] " rostedt
2019-05-03 1:51 ` Steven Rostedt
2019-05-03 9:29 ` [RFC][PATCH 1/2] " peterz
2019-05-03 9:29 ` Peter Zijlstra
2019-05-03 13:22 ` rostedt
2019-05-03 13:22 ` Steven Rostedt
2019-05-03 16:20 ` luto
2019-05-03 16:20 ` Andy Lutomirski
2019-05-03 16:31 ` rostedt
2019-05-03 16:31 ` Steven Rostedt
2019-05-03 16:35 ` peterz
2019-05-03 16:35 ` Peter Zijlstra
2019-05-03 16:44 ` luto
2019-05-03 16:44 ` Andy Lutomirski
2019-05-03 16:49 ` rostedt
2019-05-03 16:49 ` Steven Rostedt
2019-05-03 16:32 ` peterz
2019-05-03 16:32 ` Peter Zijlstra
2019-05-03 18:57 ` torvalds
2019-05-03 18:57 ` Linus Torvalds
2019-05-06 8:19 ` peterz
2019-05-06 8:19 ` Peter Zijlstra
2019-05-06 13:56 ` rostedt
2019-05-06 13:56 ` Steven Rostedt
2019-05-06 16:17 ` torvalds
2019-05-06 16:17 ` Linus Torvalds
2019-05-06 16:19 ` torvalds
2019-05-06 16:19 ` Linus Torvalds
2019-05-06 17:06 ` rostedt
2019-05-06 17:06 ` Steven Rostedt
2019-05-06 18:06 ` torvalds
2019-05-06 18:06 ` Linus Torvalds
2019-05-06 18:57 ` rostedt
2019-05-06 18:57 ` Steven Rostedt
2019-05-06 19:46 ` torvalds
2019-05-06 19:46 ` Linus Torvalds
2019-05-06 20:29 ` rostedt
2019-05-06 20:29 ` Steven Rostedt
2019-05-06 20:42 ` torvalds
2019-05-06 20:42 ` Linus Torvalds
2019-05-06 20:44 ` torvalds
2019-05-06 20:44 ` Linus Torvalds
2019-05-06 21:45 ` rostedt
2019-05-06 21:45 ` Steven Rostedt
2019-05-06 22:06 ` torvalds
2019-05-06 22:06 ` Linus Torvalds
2019-05-06 22:31 ` torvalds
2019-05-06 22:31 ` Linus Torvalds
2019-05-07 0:10 ` rostedt
2019-05-07 0:10 ` Steven Rostedt
2019-05-07 1:06 ` torvalds
2019-05-07 1:06 ` Linus Torvalds
2019-05-07 1:04 ` rostedt
2019-05-07 1:04 ` Steven Rostedt
2019-05-07 1:34 ` rostedt
2019-05-07 1:34 ` Steven Rostedt
2019-05-07 1:34 ` torvalds
2019-05-07 1:34 ` Linus Torvalds
2019-05-07 1:53 ` rostedt
2019-05-07 1:53 ` Steven Rostedt
2019-05-07 2:22 ` torvalds
2019-05-07 2:22 ` Linus Torvalds
2019-05-07 2:58 ` rostedt
2019-05-07 2:58 ` Steven Rostedt
2019-05-07 3:05 ` torvalds
2019-05-07 3:05 ` Linus Torvalds
2019-05-07 3:21 ` rostedt
2019-05-07 3:21 ` Steven Rostedt
2019-05-07 3:28 ` torvalds
2019-05-07 3:28 ` Linus Torvalds
2019-05-07 14:54 ` torvalds
2019-05-07 14:54 ` Linus Torvalds
2019-05-07 15:12 ` rostedt
2019-05-07 15:12 ` Steven Rostedt
2019-05-07 15:25 ` rostedt
2019-05-07 15:25 ` Steven Rostedt
2019-05-07 16:25 ` rostedt
2019-05-07 16:25 ` Steven Rostedt
2019-05-07 15:31 ` torvalds
2019-05-07 15:31 ` Linus Torvalds
2019-05-07 15:45 ` rostedt
2019-05-07 15:45 ` Steven Rostedt
2019-05-07 16:34 ` peterz
2019-05-07 16:34 ` Peter Zijlstra
2019-05-07 17:08 ` torvalds
2019-05-07 17:08 ` Linus Torvalds
2019-05-07 17:21 ` jpoimboe
2019-05-07 17:21 ` Josh Poimboeuf
2019-05-07 21:24 ` rostedt
2019-05-07 21:24 ` Steven Rostedt
2019-05-08 4:50 ` torvalds
2019-05-08 4:50 ` Linus Torvalds
2019-05-08 16:37 ` rostedt
2019-05-08 16:37 ` Steven Rostedt
2019-05-07 17:38 ` peterz
2019-05-07 17:38 ` Peter Zijlstra
2019-05-07 9:51 ` peterz
2019-05-07 9:51 ` Peter Zijlstra
2019-05-07 14:48 ` luto
2019-05-07 14:48 ` Andy Lutomirski
2019-05-07 14:57 ` torvalds
2019-05-07 14:57 ` Linus Torvalds
2019-05-07 14:13 ` mhiramat
2019-05-07 14:13 ` Masami Hiramatsu
2019-05-07 17:15 ` mhiramat
2019-05-07 17:15 ` Masami Hiramatsu
2019-05-06 14:22 ` peterz
2019-05-06 14:22 ` Peter Zijlstra
2019-05-07 8:57 ` peterz
2019-05-07 8:57 ` Peter Zijlstra
2019-05-07 9:18 ` David.Laight
2019-05-07 9:18 ` David Laight
2019-05-07 11:30 ` peterz
2019-05-07 11:30 ` Peter Zijlstra
2019-05-07 12:57 ` David.Laight
2019-05-07 12:57 ` David Laight
2019-05-07 13:14 ` rostedt
2019-05-07 13:14 ` Steven Rostedt
2019-05-07 14:50 ` David.Laight
2019-05-07 14:50 ` David Laight
2019-05-07 14:57 ` rostedt
2019-05-07 14:57 ` Steven Rostedt
2019-05-07 15:46 ` David.Laight
2019-05-07 15:46 ` David Laight
2019-05-07 13:32 ` peterz
2019-05-07 13:32 ` Peter Zijlstra
2019-05-07 9:27 ` peterz
2019-05-07 9:27 ` Peter Zijlstra
2019-05-07 12:27 ` rostedt
2019-05-07 12:27 ` Steven Rostedt
2019-05-07 12:41 ` peterz
2019-05-07 12:41 ` Peter Zijlstra
2019-05-07 12:54 ` rostedt
2019-05-07 12:54 ` Steven Rostedt
2019-05-07 17:22 ` masami.hiramatsu
2019-05-07 17:22 ` Masami Hiramatsu
2019-05-07 14:28 ` peterz
2019-05-07 14:28 ` Peter Zijlstra
2019-05-02 20:48 ` rostedt
2019-05-02 20:48 ` Steven Rostedt
2019-05-06 15:14 ` jpoimboe
2019-05-06 15:14 ` Josh Poimboeuf
2019-05-01 20:28 ` [RFC][PATCH 2/2] ftrace/x86: Emulate call function while updating in breakpoint handler rostedt
2019-05-01 20:28 ` Steven Rostedt
2019-05-03 10:22 ` [RFC][PATCH 1.5/2] x86: Add int3_emulate_call() selftest peterz
2019-05-03 10:22 ` Peter Zijlstra
2019-05-03 18:46 ` rostedt
2019-05-03 18:46 ` Steven Rostedt
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