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From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>,
	Christophe Leroy <christophe.leroy@c-s.fr>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: objtool clac/stac handling change..
Date: Thu, 2 Jul 2020 21:59:02 +0100	[thread overview]
Message-ID: <20200702205902.GP2786714@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAHk-=whW7qYEK-MJMS9gKf-K4cBNGTq0pv-5wo4bqE_QtUfkDw@mail.gmail.com>

On Thu, Jul 02, 2020 at 01:32:34PM -0700, Linus Torvalds wrote:

> Ugh, the above is bad anyway.
> 
> It doesn't use _ASM_EXTABLE_UA, so it won't warn about the noncanonical cases.

FWIW, the address is inside a sigframe we decided to build, so noncanonical
addresses shouldn't occur in practice.

> Yeah, it would need to be turned into a "jump out" instead of just "jump over".
> 
> Which it damn well should do anyway.,
> 
> That code should be taken behind a shed and shot. It does so many
> things wrong that it's not even funny. It shouldn't do stac/clac on
> its own.
>
> At least it could use the "user_insn()" helper, which does it inside
> the asm itself, has the right might_fault() marking (but not the
> address check), and which can be trivially changed to have the fixup
> jump be to after the "ASM_CLAC".

I'm not sure it's the right solution in this case.  Look at the call chain
and the stuff done nearby (that __clear_user(), for example)...

I'm not saying that this code is not awful - it certainly is.  But it's
not that simple, unfortunately ;-/

  reply	other threads:[~2020-07-02 20:59 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-01 18:22 objtool clac/stac handling change Linus Torvalds
2020-07-01 18:29 ` Andy Lutomirski
2020-07-01 19:35   ` Linus Torvalds
2020-07-01 20:36     ` Andy Lutomirski
2020-07-01 20:51       ` Josh Poimboeuf
2020-07-01 21:02         ` Linus Torvalds
2020-07-02  0:00           ` Josh Poimboeuf
2020-07-02  8:05             ` Peter Zijlstra
2020-07-01 20:51       ` Linus Torvalds
2020-07-02  0:47         ` Andy Lutomirski
2020-07-02  2:30           ` Linus Torvalds
2020-07-02  2:35             ` Linus Torvalds
2020-07-02  3:08             ` Andy Lutomirski
2020-07-01 18:41 ` Al Viro
2020-07-01 19:04   ` Linus Torvalds
2020-07-01 19:59     ` Al Viro
2020-07-01 20:25       ` Linus Torvalds
2020-07-02 13:34         ` Michael Ellerman
2020-07-02 14:01           ` Al Viro
2020-07-02 14:04             ` Al Viro
2020-07-02 15:13           ` Christophe Leroy
2020-07-02 20:13             ` Linus Torvalds
2020-07-03  3:59               ` Michael Ellerman
2020-07-03  3:17             ` Michael Ellerman
2020-07-03  5:27               ` Christophe Leroy
2020-07-02 19:52           ` Linus Torvalds
2020-07-02 20:17             ` Al Viro
2020-07-02 20:32               ` Linus Torvalds
2020-07-02 20:59                 ` Al Viro [this message]
2020-07-02 21:55                   ` Linus Torvalds
2020-07-03  1:33                     ` Al Viro
2020-07-03  3:32                       ` Linus Torvalds
2020-07-03 21:02                       ` Al Viro
2020-07-03 21:10                         ` Linus Torvalds
2020-07-03 21:41                           ` Andy Lutomirski
2020-07-03 22:25                             ` Al Viro
2020-07-03 21:59                           ` Al Viro
2020-07-03 22:04                             ` Al Viro
2020-07-03 22:12                           ` Al Viro
2020-07-04  0:49                         ` Al Viro
2020-07-04  1:54                           ` Linus Torvalds
2020-07-04  2:30                             ` Al Viro
2020-07-04  3:06                               ` Linus Torvalds
2020-07-04  2:11                           ` Al Viro
2020-07-07 12:35                             ` David Laight
2020-07-10 22:37                               ` Linus Torvalds
2020-07-13  9:32                                 ` David Laight

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