linux-hardening - Re: [PATCH 3/3] usercopy: Add find_vmap_area

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Message-ID: <202209160805.CA47B2D673@keescook>
Date:   Fri, 16 Sep 2022 08:09:16 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Uladzislau Rezki <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yu Zhao <yuzhao@...gle.com>, dev@...-flo.net,
        linux-mm@...ck.org, linux-hardening@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-perf-users@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [PATCH 3/3] usercopy: Add find_vmap_area_try() to avoid deadlocks

On Fri, Sep 16, 2022 at 03:46:07PM +0100, Matthew Wilcox wrote:
> On Fri, Sep 16, 2022 at 06:59:57AM -0700, Kees Cook wrote:
> > The check_object_size() checks under CONFIG_HARDENED_USERCOPY need to be
> > more defensive against running from interrupt context. Use a best-effort
> > check for VMAP areas when running in interrupt context
> 
> I had something more like this in mind:

Yeah, I like -EAGAIN. I'd like to keep the interrupt test to choose lock
vs trylock, otherwise it's trivial to bypass the hardening test by having
all the other CPUs beating on the spinlock.

Thanks!

-Kees

-- 
Kees Cook