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From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	"Tobin C . Harding" <me@tobin.cc>, Michal Hocko <mhocko@suse.cz>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	linux-kernel@vger.kernel.org,
	Michael Ellerman <mpe@ellerman.id.au>,
	linuxppc-dev@lists.ozlabs.org, Russell Currey <ruscur@russell.cc>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
	Stephen Rothwell <sfr@ozlabs.org>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	linux-arch@vger.kernel.org, linux-s390@vger.kernel.org,
	Martin Schwidefsky <schwidefsky@de.ibm.com>
Subject: Re: [PATCH] vsprintf: Do not break early boot with probing addresses
Date: Fri, 10 May 2019 13:32:00 +0900	[thread overview]
Message-ID: <20190510043200.GC15652@jagdpanzerIV> (raw)
In-Reply-To: <20190509121923.8339-1-pmladek@suse.com>

On (05/09/19 14:19), Petr Mladek wrote:
> 1. Report on Power:
> 
> Kernel crashes very early during boot with with CONFIG_PPC_KUAP and
> CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG
> 
> The problem is the combination of some new code called via printk(),
> check_pointer() which calls probe_kernel_read(). That then calls
> allow_user_access() (PPC_KUAP) and that uses mmu_has_feature() too early
> (before we've patched features). With the JUMP_LABEL debug enabled that
> causes us to call printk() & dump_stack() and we end up recursing and
> overflowing the stack.

Hmm... hmm... PPC does an .opd-based symbol dereference, which
eventually probe_kernel_read()-s. So early printk(%pS) will do

	printk(%pS)
	 dereference_function_descriptor()
	  probe_kernel_address()
	   dump_stack()
	    printk(%pS)
	     dereference_function_descriptor()
	      probe_kernel_address()
	       dump_stack()
	        printk(%pS)
	         ...

I'd say... that it's not vsprintf that we want to fix, it's
the idea that probe_kernel_address() can dump_stack() on any
platform. On some archs probe_kernel_address()->dump_stack()
is going nowhere:
 dump_stack() does probe_kernel_address(), which calls dump_stack(),
 which calls printk(%pS)->probe_kernel_address() again and again,
 and again.

	-ss

  parent reply	other threads:[~2019-05-10  4:32 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-09 12:19 Petr Mladek
2019-05-09 13:05 ` Andy Shevchenko
2019-05-09 13:13 ` Steven Rostedt
2019-05-09 14:06   ` Petr Mladek
2019-05-09 13:38 ` Michal Suchánek
2019-05-09 13:46   ` David Laight
2019-05-10 10:21     ` Michael Ellerman
2019-05-10  4:32 ` Sergey Senozhatsky [this message]
     [not found]   ` <CAHk-=wiP+hwSqEW0dM6AYNWUR7jXDkeueq69et6ahfUgV7hC3w@mail.gmail.com>
2019-05-10  5:07     ` Sergey Senozhatsky
2019-05-10  6:41       ` Michael Ellerman
2019-05-10  8:06       ` Petr Mladek
2019-05-10  8:16         ` Sergey Senozhatsky
2019-05-10  8:42           ` Petr Mladek
2019-05-10  8:51             ` Sergey Senozhatsky
2019-05-10 14:49             ` Petr Mladek
2019-05-10 16:24             ` Steven Rostedt
2019-05-10 16:32               ` Martin Schwidefsky
2019-05-10 16:40                 ` Steven Rostedt
2019-05-10 16:45                   ` Martin Schwidefsky
2019-05-13 12:24                   ` Petr Mladek
2019-05-10 16:41               ` Andy Shevchenko
2019-05-10 17:35               ` christophe leroy
2019-05-13  8:52                 ` David Laight
2019-05-13  9:13                   ` Andy Shevchenko
2019-05-13 12:42                     ` Petr Mladek
2019-05-13 14:15                       ` Steven Rostedt
2019-05-14  2:07                       ` Sergey Senozhatsky
2019-05-14  2:25                         ` Sergey Senozhatsky
2019-05-14  8:28                         ` David Laight
2019-05-14  9:02                           ` Geert Uytterhoeven
2019-05-14 18:37                             ` Steven Rostedt
2019-05-14 19:13                               ` Geert Uytterhoeven
2019-05-14 19:35                                 ` Steven Rostedt
2019-05-15  7:23                                   ` Geert Uytterhoeven
2019-05-15  7:53                                     ` Petr Mladek
2019-05-15  6:21                                 ` Sergey Senozhatsky
2019-05-15  7:35                               ` Petr Mladek
2019-05-15  9:00                                 ` David Laight

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