All of lore.kernel.org
 help / color / mirror / Atom feed
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

WARNING: multiple messages have this Message-ID (diff)
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: linux-arch@vger.kernel.org,
	Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	linux-s390@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	linux-kernel@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	Michal Hocko <mhocko@suse.cz>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Stephen Rothwell <sfr@ozlabs.org>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	"Tobin C . Harding" <me@tobin.cc>
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: 95+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-09 12:19 [PATCH] vsprintf: Do not break early boot with probing addresses Petr Mladek
2019-05-09 12:19 ` Petr Mladek
2019-05-09 13:05 ` Andy Shevchenko
2019-05-09 13:05   ` Andy Shevchenko
2019-05-09 13:13 ` Steven Rostedt
2019-05-09 13:13   ` Steven Rostedt
2019-05-09 14:06   ` Petr Mladek
2019-05-09 14:06     ` Petr Mladek
2019-05-09 13:38 ` Michal Suchánek
2019-05-09 13:38   ` Michal Suchánek
2019-05-09 13:46   ` David Laight
2019-05-09 13:46     ` David Laight
2019-05-10 10:21     ` Michael Ellerman
2019-05-10 10:21       ` Michael Ellerman
2019-05-10 10:21       ` Michael Ellerman
2019-05-10  4:32 ` Sergey Senozhatsky [this message]
2019-05-10  4:32   ` Sergey Senozhatsky
2019-05-10  4:47   ` Linus Torvalds
2019-05-10  5:07     ` Sergey Senozhatsky
2019-05-10  5:07       ` Sergey Senozhatsky
2019-05-10  6:41       ` Michael Ellerman
2019-05-10  6:41         ` Michael Ellerman
2019-05-10  6:41         ` Michael Ellerman
2019-05-10  6:41         ` Michael Ellerman
2019-05-10  8:06       ` Petr Mladek
2019-05-10  8:06         ` Petr Mladek
2019-05-10  8:16         ` Sergey Senozhatsky
2019-05-10  8:16           ` Sergey Senozhatsky
2019-05-10  8:42           ` Petr Mladek
2019-05-10  8:42             ` Petr Mladek
2019-05-10  8:51             ` Sergey Senozhatsky
2019-05-10  8:51               ` Sergey Senozhatsky
2019-05-10 14:49             ` Petr Mladek
2019-05-10 14:49               ` Petr Mladek
2019-05-10 16:24             ` Steven Rostedt
2019-05-10 16:24               ` Steven Rostedt
2019-05-10 16:32               ` Martin Schwidefsky
2019-05-10 16:32                 ` Martin Schwidefsky
2019-05-10 16:40                 ` Steven Rostedt
2019-05-10 16:40                   ` Steven Rostedt
2019-05-10 16:45                   ` Martin Schwidefsky
2019-05-10 16:45                     ` Martin Schwidefsky
2019-05-13 12:24                   ` Petr Mladek
2019-05-13 12:24                     ` Petr Mladek
2019-05-10 16:41               ` Andy Shevchenko
2019-05-10 16:41                 ` Andy Shevchenko
2019-05-10 17:35               ` christophe leroy
2019-05-10 17:35                 ` christophe leroy
2019-05-13  8:52                 ` David Laight
2019-05-13  8:52                   ` David Laight
2019-05-13  9:13                   ` Andy Shevchenko
2019-05-13  9:13                     ` Andy Shevchenko
2019-05-13  9:13                     ` Andy Shevchenko
2019-05-13 12:42                     ` Petr Mladek
2019-05-13 12:42                       ` Petr Mladek
2019-05-13 12:42                       ` Petr Mladek
2019-05-13 14:15                       ` Steven Rostedt
2019-05-13 14:15                         ` Steven Rostedt
2019-05-13 14:15                         ` Steven Rostedt
2019-05-14  2:07                       ` Sergey Senozhatsky
2019-05-14  2:07                         ` Sergey Senozhatsky
2019-05-14  2:07                         ` Sergey Senozhatsky
2019-05-14  2:25                         ` Sergey Senozhatsky
2019-05-14  2:25                           ` Sergey Senozhatsky
2019-05-14  2:25                           ` Sergey Senozhatsky
2019-05-14  8:28                         ` David Laight
2019-05-14  8:28                           ` David Laight
2019-05-14  8:28                           ` David Laight
2019-05-14  9:02                           ` Geert Uytterhoeven
2019-05-14  9:02                             ` Geert Uytterhoeven
2019-05-14  9:02                             ` Geert Uytterhoeven
2019-05-14 18:37                             ` Steven Rostedt
2019-05-14 18:37                               ` Steven Rostedt
2019-05-14 18:37                               ` Steven Rostedt
2019-05-14 19:13                               ` Geert Uytterhoeven
2019-05-14 19:13                                 ` Geert Uytterhoeven
2019-05-14 19:13                                 ` Geert Uytterhoeven
2019-05-14 19:35                                 ` Steven Rostedt
2019-05-14 19:35                                   ` Steven Rostedt
2019-05-14 19:35                                   ` Steven Rostedt
2019-05-15  7:23                                   ` Geert Uytterhoeven
2019-05-15  7:23                                     ` Geert Uytterhoeven
2019-05-15  7:23                                     ` Geert Uytterhoeven
2019-05-15  7:53                                     ` Petr Mladek
2019-05-15  7:53                                       ` Petr Mladek
2019-05-15  7:53                                       ` Petr Mladek
2019-05-15  6:21                                 ` Sergey Senozhatsky
2019-05-15  6:21                                   ` Sergey Senozhatsky
2019-05-15  6:21                                   ` Sergey Senozhatsky
2019-05-15  7:35                               ` Petr Mladek
2019-05-15  7:35                                 ` Petr Mladek
2019-05-15  7:35                                 ` Petr Mladek
2019-05-15  9:00                                 ` David Laight
2019-05-15  9:00                                   ` David Laight
2019-05-15  9:00                                   ` David Laight

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=20190510043200.GC15652@jagdpanzerIV \
    --to=sergey.senozhatsky.work@gmail.com \
    --cc=andriy.shevchenko@linux.intel.com \
    --cc=christophe.leroy@c-s.fr \
    --cc=heiko.carstens@de.ibm.com \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-s390@vger.kernel.org \
    --cc=linux@rasmusvillemoes.dk \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=me@tobin.cc \
    --cc=mhocko@suse.cz \
    --cc=mpe@ellerman.id.au \
    --cc=pmladek@suse.com \
    --cc=rostedt@goodmis.org \
    --cc=ruscur@russell.cc \
    --cc=schwidefsky@de.ibm.com \
    --cc=sergey.senozhatsky@gmail.com \
    --cc=sfr@ozlabs.org \
    --cc=torvalds@linux-foundation.org \
    /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.