From: Michael Schmitz <schmitzmic@gmail.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-m68k@lists.linux-m68k.org,
Geert Uytterhoeven <geert@linux-m68k.org>,
Greg Ungerer <gerg@linux-m68k.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] m68k: leave stack mangling to asm wrapper of sigreturn()
Date: Thu, 16 Sep 2021 17:02:22 +1200 [thread overview]
Message-ID: <59a44e17-bff8-041e-b704-2b1d97601ce7@gmail.com> (raw)
In-Reply-To: <YUK4MWzI73lwRq0W@zeniv-ca.linux.org.uk>
Hi Al,
On 16/09/21 15:21, Al Viro wrote:
> On Thu, Sep 16, 2021 at 12:53:53PM +1200, Michael Schmitz wrote:
>>> IOW, what would be the benefit of trying to avoid unconditional gap there?
>>
>> Avoiding a kernel stack overflow - there are comments in the code that warn
>> against that, but those may be largely historic...
>
> This is syscall entry; moreover, it critically relies upon the fixed stack
> layout - type 0 exception frame + pt_regs + switch_stack + (now) gap.
AFAIR, the concerns in the comments I saw were about interrupts - come
to think of it, back in the early days, we used to have 'fast' and
'slow' interrupt handlers, with much of the heavy lifting done in the
handler, and slow interrupts allowed to lower the IPL. Probably no
longer relevant.
> Followed by fairly shallow C call chain. I suspect that the deepest you
> can get there is when you get an unmapped page when reading the sigframe
> and go into page fault handling, with call chain going into some filesystem's
> ->readpage(). If it was that close to stack overflow, we'd see them all
> the time in e.g. random net ioctl doing copy_from_user() - that's going
> to be deeper. Or in stat(2), for that matter.
Your points are well taken - I can see now that my concerns are without
merit.
The only question that remains is whether the third patch can also go to
-stable. Most of my testing was with all three patches applied, I can
drop the third one and retest if you're worries the third one is not
appropriate for -stable.
Cheers,
Michael
next prev parent reply other threads:[~2021-09-16 5:04 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-07-25 17:18 [RFC][CFT] signal handling fixes Al Viro
2021-07-25 17:19 ` [PATCH 1/3] m68k: handle arrivals of multiple signals correctly Al Viro
2021-09-15 22:08 ` Michael Schmitz
2021-07-25 17:19 ` [PATCH 2/3] m68k: update ->thread.esp0 before calling syscall_trace() in ret_from_signal Al Viro
2021-09-15 22:19 ` Michael Schmitz
2021-07-25 17:20 ` [PATCH 3/3] m68k: leave stack mangling to asm wrapper of sigreturn() Al Viro
2021-09-15 23:35 ` Michael Schmitz
2021-09-16 0:19 ` Al Viro
2021-09-16 0:53 ` Michael Schmitz
2021-09-16 3:21 ` Al Viro
2021-09-16 5:02 ` Michael Schmitz [this message]
2021-09-16 16:14 ` Al Viro
2021-07-27 10:21 ` [RFC][CFT] signal handling fixes Finn Thain
2021-07-27 14:42 ` Al Viro
2021-07-28 1:23 ` Finn Thain
2021-08-11 1:42 ` Finn Thain
2021-09-16 9:03 ` Finn Thain
2021-09-23 14:43 ` Geert Uytterhoeven
2021-09-23 14:45 ` Geert Uytterhoeven
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=59a44e17-bff8-041e-b704-2b1d97601ce7@gmail.com \
--to=schmitzmic@gmail.com \
--cc=geert@linux-m68k.org \
--cc=gerg@linux-m68k.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-m68k@lists.linux-m68k.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.