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Message-ID: <20170508204858.GT29622@ZenIV.linux.org.uk>
Date: Mon, 8 May 2017 21:48:58 +0100
From: Al Viro <viro@...IV.linux.org.uk>
To: Jann Horn <jannh@...gle.com>
Cc: 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>,
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Catalin Marinas <catalin.marinas@....com>,
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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 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.
BTW, that's a nice example demonstrating why doing that on the kernel
boundary is wrong. Wider (in theory) area being "protected" => easier
to miss the ways not crossing its border.
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