lkml.org 
[lkml]   [2021]   [Feb]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectWhy do kprobes and uprobes singlestep?
A while back, I let myself be convinced that kprobes genuinely need to
single-step the kernel on occasion, and I decided that this sucked but
I could live with it. it would, however, be Really Really Nice (tm)
if we could have a rule that anyone running x86 Linux who single-steps
the kernel (e.g. kgdb and nothing else) gets to keep all the pieces
when the system falls apart around them. Specifically, if we don't
allow kernel single-stepping and if we suitably limit kernel
instruction breakpoints (the latter isn't actually a major problem),
then we don't really really need to use IRET to return to the kernel,
and that means we can avoid some massive NMI nastiness.

But I was contemplating the code, and I'm no longer convinced.
Uprobes seem to single-step user code for no discernable reason.
(They want to trap after executing an out of line instruction, AFAICT.
Surely INT3 or even CALL after the out-of-line insn would work as well
or better.) Why does kprobe single-step? I spend a while staring at
the code, and it was entirely unclear to me what the purpose of the
single-step is.

--Andy

\
 
 \ /
  Last update: 2021-02-24 00:38    [W:0.831 / U:0.096 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site