From: Andy Lutomirski <luto@amacapital.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>, Peter Anvin <hpa@zytor.com>,
Julien Thierry <julien.thierry@arm.com>,
Will Deacon <will.deacon@arm.com>, Ingo Molnar <mingo@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
James Morse <james.morse@arm.com>,
valentin.schneider@arm.com, Brian Gerst <brgerst@gmail.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Andrew Lutomirski <luto@kernel.org>,
Borislav Petkov <bp@alien8.de>,
Denys Vlasenko <dvlasenk@redhat.com>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [PATCH 6/8] i915,uaccess: Fix redundant CLAC
Date: Fri, 1 Mar 2019 07:27:47 -0800 [thread overview]
Message-ID: <6D332336-71DF-463A-B07A-5D91087F133A@amacapital.net> (raw)
In-Reply-To: <20190301143800.GT32534@hirez.programming.kicks-ass.net>
> On Mar 1, 2019, at 6:38 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
>> On Fri, Mar 01, 2019 at 01:57:18PM +0100, Peter Zijlstra wrote:
>>> On Fri, Mar 01, 2019 at 01:27:45PM +0100, Peter Zijlstra wrote:
>>> arch/x86/lib/usercopy_64.o: warning: objtool: .altinstr_replacement+0x30: redundant UACCESS disable
>>
>>> The usercopy one is difficult, that's copy_user_handle_tail(), it is
>>> buggered though, because that lacks notrace and thus has a __fentry__
>>> call in.
>>>
>>> Also, afaict all exception jumps into copy_user_handle_tail() will have
>>> AC=1, but the __{get,put}_user_nocheck() things do STAC/CLAC all over
>>> again.
>>>
>>> So what do we do? Annotate that we start with AC=1 and then immediately
>>> do the clac, and then let __{get,put}_user_nocheck() do their own thing?
>>> or make it use the unsafe stuff?
>>
>> Or.. we move the thing to assembly. Of course, I suck at (writing) asm,
>> so the below is probably broken in various ways.
>
> The advantage is that it now all lives in the same .o file and objtool
> can actually follow and find the complete control flow.
>
> I've made it ENDPROC() such that it becomes STT_FUNC and objtool does
> all the normal things. I've also moved the ALIGN_DESTINATION macro into
> the .S file.
>
> Andy, do we have a sensible self-test for this path?
Not that I know of. Something like my (rejected) strncpy_from_user test could probably be added fairly easily.
next prev parent reply other threads:[~2019-03-01 15:27 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-28 14:54 [PATCH 0/8] objtool: UACCESS validation v2 Peter Zijlstra
2019-02-28 14:54 ` [PATCH 1/8] kasan,x86: Frob kasan_report() in an exception Peter Zijlstra
2019-02-28 15:22 ` Dmitry Vyukov
2019-02-28 15:45 ` Peter Zijlstra
2019-02-28 15:52 ` Dmitry Vyukov
2019-02-28 16:01 ` Andrey Ryabinin
2019-02-28 16:03 ` Dmitry Vyukov
2019-02-28 17:46 ` Peter Zijlstra
2019-02-28 18:18 ` Dmitry Vyukov
2019-03-01 14:45 ` Peter Zijlstra
2019-03-01 15:06 ` Dmitry Vyukov
2019-03-01 15:23 ` Peter Zijlstra
2019-03-06 13:13 ` Peter Zijlstra
2019-03-06 13:39 ` Dmitry Vyukov
2019-03-06 13:57 ` Peter Zijlstra
2019-03-06 14:01 ` Dmitry Vyukov
2019-03-06 14:12 ` Peter Zijlstra
2019-03-06 14:34 ` Peter Zijlstra
2019-03-06 14:40 ` Dmitry Vyukov
2019-03-06 14:41 ` Dmitry Vyukov
2019-03-06 14:55 ` Peter Zijlstra
2019-03-06 15:01 ` Dmitry Vyukov
2019-03-06 17:14 ` Peter Zijlstra
2019-03-06 17:27 ` Linus Torvalds
2019-03-06 17:37 ` Peter Zijlstra
2019-03-06 17:59 ` Linus Torvalds
2019-03-07 13:49 ` Peter Zijlstra
2019-02-28 14:54 ` [PATCH 2/8] x86/ia32: Fix ia32_restore_sigcontext AC leak Peter Zijlstra
2019-02-28 14:54 ` [PATCH 3/8] objtool: Set insn->func for alternatives Peter Zijlstra
2019-02-28 14:54 ` [PATCH 4/8] objtool: Hande function aliases Peter Zijlstra
2019-02-28 14:54 ` [PATCH 5/8] objtool: Rewrite add_ignores() Peter Zijlstra
2019-02-28 14:54 ` [PATCH 6/8] i915,uaccess: Fix redundant CLAC Peter Zijlstra
2019-02-28 15:10 ` Chris Wilson
2019-02-28 15:24 ` Peter Zijlstra
2019-02-28 16:49 ` Linus Torvalds
2019-02-28 17:51 ` Peter Zijlstra
2019-02-28 18:01 ` Peter Zijlstra
2019-02-28 18:29 ` Linus Torvalds
2019-02-28 19:01 ` Peter Zijlstra
2019-03-01 10:34 ` Peter Zijlstra
2019-03-01 12:27 ` Peter Zijlstra
2019-03-01 12:57 ` Peter Zijlstra
2019-03-01 14:38 ` Peter Zijlstra
2019-03-01 15:27 ` Andy Lutomirski [this message]
2019-03-01 16:15 ` Linus Torvalds
2019-03-01 16:17 ` Linus Torvalds
2019-02-28 14:54 ` [PATCH 7/8] objtool: Add UACCESS validation Peter Zijlstra
2019-02-28 14:54 ` [PATCH 8/8] objtool: Add Direction Flag validation Peter Zijlstra
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