linux-kernel - Re: 2.6.23 regression: accessing invalid mmap'ed memory from gdb causes unkillable spinning

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 30 Oct 2007 23:56:00 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	npiggin@...e.de
Cc:	duaneg@...da.com, mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: 2.6.23 regression: accessing invalid mmap'ed memory from gdb
 causes unkillable spinning

From: Nick Piggin <npiggin@...e.de>
Date: Wed, 31 Oct 2007 07:42:21 +0100

> Sysrq+T fails to show the stack trace of a running task. Presumably this
> is to avoid a garbled stack, however it can often be useful, and besides
> there is no guarantee that the task won't start running in the middle of
> show_stack(). If there are any correctness issues, then the archietcture
> would have to take further steps to ensure the task is not running.
> 
> Signed-off-by: Nick Piggin <npiggin@...e.de>

This is useful.

Even more useful would be a show_regs() on the cpu where running tasks
are running.  If not a full show_regs() at least a program counter.

That's usually what you're trying to debug and we provide nearly no
way to handle: some task is stuck in a loop in kernel mode and you
need to know exactly where that is.

This is pretty easy to do on sparc64.  In fact I can capture remote
cpu registers even when that CPU's interrupts are disabled.  I suppose
other arches could do a NMI'ish register capture like this as well.

I have a few bug reports that I can't make more progress on because I
currently can't ask users to do something to fetch the registers on
the seemingly hung processor.  This is why I'm harping on this so
much :-)

Anyways, my core suggestion is to add a hook here so platforms can
do the remote register fetch if they want.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/