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From: Peter Zijlstra <peterz@infradead.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	syzbot <syzbot+488ddf8087564d6de6e2@syzkaller.appspotmail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk,
	will@kernel.org, x86@kernel.org
Subject: Re: [syzbot] upstream test error: KASAN: invalid-access Read in __entry_tramp_text_end
Date: Wed, 29 Sep 2021 11:59:51 +0200	[thread overview]
Message-ID: <YVQ5F9aT7oSEKenh@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210929085035.GA33284@C02TD0UTHF1T.local>

On Wed, Sep 29, 2021 at 09:50:45AM +0100, Mark Rutland wrote:
> On Wed, Sep 29, 2021 at 09:39:47AM +0200, Peter Zijlstra wrote:
> > On Tue, Sep 28, 2021 at 06:36:37PM -0700, Josh Poimboeuf wrote:

> > > +	asm volatile("417: rdmsr\n"
> > > +		     : EAX_EDX_RET(val, low, high)
> > > +		     : "c" (msr));
> > > +	asm_volatile_goto(_ASM_EXTABLE(417b, %l[Efault]) :::: Efault);
> > 
> > That's terrible :-) Could probably do with a comment, but might just
> > work..
> 
> The compiler is well within its rights to spill/restore/copy/shuffle
> registers or modify memory between the two asm blocks (which it's liable
> to do that when optimizing this after a few layers of inlining), and
> skipping that would cause all sorts of undefined behaviour.

Ah, but in this case it'll work irrespective of that (which is why we
needs a comment!).

This is because _ASM_EXTABLE only generates data for another section.
There doesn't need to be code continuity between these two asm
statements.

As I said, this is terrible :-)

WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Mark Rutland <mark.rutland@arm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	syzbot <syzbot+488ddf8087564d6de6e2@syzkaller.appspotmail.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	syzkaller-bugs@googlegroups.com, viro@zeniv.linux.org.uk,
	will@kernel.org, x86@kernel.org
Subject: Re: [syzbot] upstream test error: KASAN: invalid-access Read in __entry_tramp_text_end
Date: Wed, 29 Sep 2021 11:59:51 +0200	[thread overview]
Message-ID: <YVQ5F9aT7oSEKenh@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20210929085035.GA33284@C02TD0UTHF1T.local>

On Wed, Sep 29, 2021 at 09:50:45AM +0100, Mark Rutland wrote:
> On Wed, Sep 29, 2021 at 09:39:47AM +0200, Peter Zijlstra wrote:
> > On Tue, Sep 28, 2021 at 06:36:37PM -0700, Josh Poimboeuf wrote:

> > > +	asm volatile("417: rdmsr\n"
> > > +		     : EAX_EDX_RET(val, low, high)
> > > +		     : "c" (msr));
> > > +	asm_volatile_goto(_ASM_EXTABLE(417b, %l[Efault]) :::: Efault);
> > 
> > That's terrible :-) Could probably do with a comment, but might just
> > work..
> 
> The compiler is well within its rights to spill/restore/copy/shuffle
> registers or modify memory between the two asm blocks (which it's liable
> to do that when optimizing this after a few layers of inlining), and
> skipping that would cause all sorts of undefined behaviour.

Ah, but in this case it'll work irrespective of that (which is why we
needs a comment!).

This is because _ASM_EXTABLE only generates data for another section.
There doesn't need to be code continuity between these two asm
statements.

As I said, this is terrible :-)

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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-09-29 10:02 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-04 11:57 [syzbot] upstream test error: KASAN: invalid-access Read in __entry_tramp_text_end syzbot
2021-09-17 15:03 ` Dmitry Vyukov
2021-09-17 15:03   ` Dmitry Vyukov
2021-09-21 16:51   ` Mark Rutland
2021-09-21 16:51     ` Mark Rutland
2021-09-27 14:27     ` Dmitry Vyukov
2021-09-27 14:27       ` Dmitry Vyukov
2021-09-27 14:30       ` Dmitry Vyukov
2021-09-27 14:30         ` Dmitry Vyukov
2021-09-27 17:01       ` Mark Rutland
2021-09-27 17:01         ` Mark Rutland
2021-09-27 17:18         ` Mark Rutland
2021-09-27 17:18           ` Mark Rutland
2021-09-28 10:19           ` Dmitry Vyukov
2021-09-28 10:19             ` Dmitry Vyukov
2021-09-28 10:35             ` Mark Rutland
2021-09-28 10:35               ` Mark Rutland
2021-09-29  1:36               ` Josh Poimboeuf
2021-09-29  1:36                 ` Josh Poimboeuf
2021-09-29  7:39                 ` Peter Zijlstra
2021-09-29  7:39                   ` Peter Zijlstra
2021-09-29  8:50                   ` Mark Rutland
2021-09-29  8:50                     ` Mark Rutland
2021-09-29  9:59                     ` Peter Zijlstra [this message]
2021-09-29  9:59                       ` Peter Zijlstra
2021-09-29 10:37                       ` Mark Rutland
2021-09-29 10:37                         ` Mark Rutland
2021-09-29 11:43                         ` Peter Zijlstra
2021-09-29 11:43                           ` Peter Zijlstra
2021-09-30 19:26                           ` Josh Poimboeuf
2021-09-30 19:26                             ` Josh Poimboeuf
2021-10-01 12:27                             ` Mark Rutland
2021-10-01 12:27                               ` Mark Rutland
2021-10-02  5:10                               ` Josh Poimboeuf
2021-10-02  5:10                                 ` Josh Poimboeuf

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