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Subject: Re: [PATCH 1/2] alpha/ptrace: Record and handle the absence of
 switch_stack
To:     Linus Torvalds <torvalds@linux-foundation.org>
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Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
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From:   Michael Schmitz <schmitzmic@gmail.com>
Message-ID: <60c0fe00-b966-6385-d348-f6dd45277113@gmail.com>
Date:   Mon, 21 Jun 2021 15:18:35 +1200
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Hi Linus,

Am 21.06.2021 um 14:17 schrieb Linus Torvalds:
> On Sun, Jun 20, 2021 at 7:01 PM Michael Schmitz <schmitzmic@gmail.com> wrote:
>>
>> instrumenting get_reg on m68k and using a similar patch to yours to warn
>> when unsaved registers are accessed on the switch stack, I get a hit
>> from getegid and getegid32, just by running a simple ptrace on ls.
>>
>> Going to wack those two moles now ...
>
> I don't see what's going on. Those system calls don't use the register
> state, afaik. What's the call chain, exactly?

This is what I get from WARN_ONCE:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 1177 at arch/m68k/kernel/ptrace.c:91 get_reg+0x90/0xb8
Modules linked in:
CPU: 0 PID: 1177 Comm: strace Not tainted 
5.13.0-rc1-atari-fpuemu-exitfix+ #1146
Stack from 014b7f04:
         014b7f04 00336401 00336401 000278f0 0032c015 0000005b 00000005 
0002795a
         0032c015 0000005b 0000338c 00000009 00000000 00000000 ffffffe4 
00000005
         00000003 00000014 00000003 00000014 efc2b90c 0000338c 0032c015 
0000005b
         00000009 00000000 efc2b908 00912540 efc2b908 000034cc 00912540 
00000005
         00000000 efc2b908 00000003 00912540 8000110c c010b0a4 efc2b90c 
0002d1d8
         00912540 00000003 00000014 efc2b908 0000049a 00000014 efc2b908 
800acaa8
Call Trace: [<000278f0>] __warn+0x9e/0xb4
  [<0002795a>] warn_slowpath_fmt+0x54/0x62
  [<0000338c>] get_reg+0x90/0xb8
  [<0000338c>] get_reg+0x90/0xb8
  [<000034cc>] arch_ptrace+0x7e/0x250
  [<0002d1d8>] sys_ptrace+0x232/0x2f8
  [<00002ab6>] syscall+0x8/0xc
  [<0000c00b>] lower+0x7/0x20

---[ end trace ee4be53b94695793 ]---

Syscall numbers are actually 90 and 192 - sys_old_mmap and sys_mmap2 on 
m68k. Used the calculator on my Ubuntu desktop, that appears to be a 
little confused about hex to decimal conversions.

I hope that makes more sense?

Cheers,

	Michael

>
>            Linus
>