From: Linus Torvalds <torvalds@linux-foundation.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
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 12:52:27 -0700 [thread overview]
Message-ID: <CAHk-=wicOPQwuDUzFyDTBgr4UvQJHPdCX7_6BLaK6cve6CqBSg@mail.gmail.com> (raw)
In-Reply-To: <87lfk26nx4.fsf@mpe.ellerman.id.au>
On Thu, Jul 2, 2020 at 6:32 AM Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> Probably the simplest option for us is to just handle it in our
> unsafe_op_wrap(). I'll try and come up with something tomorrow.
IMy suggestion was to basically just always handle it in all exception cases.
And note that IU don't mean the fault handler: obviously page faults
(or unaligned faults or whatever) can happen while in a user access
region.
But I mean any time fixup_exception() triggers.
For x86, this is in fact particularly natural: it involves just always
clearing the AC bit in the "struct pt_regs" that fixup_exception()
gets anyway. We can do it without even bothering with checking for
CLAC/STAC support, since without it, AC is meaningless in kernel mode
anyway, but also because doing "user_access_end()" in the exception
would be pointless: AC is restored by the exception routine, so on x86
you *have* to do it by just modifying the return state.
Linus
next prev parent reply other threads:[~2020-07-02 19:52 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 [this message]
2020-07-02 20:17 ` Al Viro
2020-07-02 20:32 ` Linus Torvalds
2020-07-02 20:59 ` Al Viro
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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