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Message-ID: <CALCETrXv1-B=gc3eWcgsztr6vdao6fs9U8ATNK8t414GkVCObw@mail.gmail.com>
Date: Fri, 12 May 2017 16:15:56 -0700
From: Andy Lutomirski <luto@...nel.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: Jann Horn <jannh@...gle.com>, Ingo Molnar <mingo@...nel.org>,
Kees Cook <keescook@...omium.org>, Thomas Garnier <thgarnie@...gle.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>, Heiko Carstens <heiko.carstens@...ibm.com>,
Dave Hansen <dave.hansen@...el.com>, Arnd Bergmann <arnd@...db.de>,
Thomas Gleixner <tglx@...utronix.de>, David Howells <dhowells@...hat.com>,
René Nyffenegger <mail@...enyffenegger.ch>,
Andrew Morton <akpm@...ux-foundation.org>,
"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>, "Eric W . Biederman" <ebiederm@...ssion.com>,
Oleg Nesterov <oleg@...hat.com>, Pavel Tikhomirov <ptikhomirov@...tuozzo.com>,
Ingo Molnar <mingo@...hat.com>, "H . Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>,
Paolo Bonzini <pbonzini@...hat.com>, Rik van Riel <riel@...hat.com>,
Josh Poimboeuf <jpoimboe@...hat.com>, Borislav Petkov <bp@...en8.de>, Brian Gerst <brgerst@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
Christian Borntraeger <borntraeger@...ibm.com>, Russell King <linux@...linux.org.uk>,
Will Deacon <will.deacon@....com>, Catalin Marinas <catalin.marinas@....com>,
Mark Rutland <mark.rutland@....com>, James Morse <james.morse@....com>,
linux-s390 <linux-s390@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
Linux API <linux-api@...r.kernel.org>, "the arch/x86 maintainers" <x86@...nel.org>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
Linus Torvalds <torvalds@...ux-foundation.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH v9 1/4] syscalls: Verify address limit before returning to user-mode
On Mon, May 8, 2017 at 1:48 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Mon, May 08, 2017 at 04:06:35PM +0200, Jann Horn wrote:
>
>> I think Kees might be talking about
>> https://bugs.chromium.org/p/project-zero/issues/detail?id=822, fixed in
>> commit e6978e4bf181fb3b5f8cb6f71b4fe30fbf1b655c. The issue was that
>> perf code that can run in pretty much any context called access_ok().
>
> And that commit has *NOT* solved the problem. perf_callchain_user()
> can be called synchronously, without passing through that code.
> Tracepoint shite...
>
> That set_fs() should be done in get_perf_callchain(), just around the call of
> perf_callchain_user(). Along with pagefault_disable(), actually.
>
Even that's not quite enough because of a different issue: perf nmis
can hit during scheduling or when we're in lazy mm, leading to the
entirely wrong set of page tables being used. We need
nmi_uaccess_begin() and nmi_uaccess_end(), and the former needs to be
allowed to fail.
AFAIK this isn't presently a security problem because it mainly
affects kernel threads, and you need to be root to profile them, but
maybe there's some race where it does matter.
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