linux-kernel - Re: [PATCH] arm64: kernel: memory corruptions due non-disabled PAN

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Message-ID: <CA+CK2bCX+QGMPzhjj-UmVNb1jG8Z6WNW=L0GiVsTpGrhyqb9tA@mail.gmail.com>
Date:   Wed, 20 Nov 2019 14:46:03 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     James Morris <jmorris@...ei.org>, Sasha Levin <sashal@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>, will@...nel.org,
        steve.capper@....com,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Marc Zyngier <marc.zyngier@....com>,
        James Morse <james.morse@....com>,
        Vladimir Murzin <vladimir.murzin@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        allison@...utok.net, info@...ux.net, alexios.zavras@...el.com
Subject: Re: [PATCH] arm64: kernel: memory corruptions due non-disabled PAN

> > I see that with CONFIG_ARM64_SW_TTBR0_PAN=y, this means that we may
> > leave the stale TTBR0 value installed across a context-switch (and have
> > reproduced that locally), but I'm having some difficulty reproducing the
> > corruption that you see.
>
> I will send the full test shortly. Note, I was never able to reproduce
> it in QEMU, only on real hardware. Also, for some unknown reason after
> kexec I could not reproduce it only during first boot, so it is
> somewhat fragile, but I am sure it can be reproduced in other cases as
> well, it is just my reproducer is not tunes for that.
>

Attached is the test program that I used to reproduce memory corruption.
Test on board with Broadcom's Stingray SoC.

Without fix:
# time /tmp/repro
Corruption: pid 1474 map[0] 1488 cpu 3
Terminated

real    0m0.088s
user    0m0.004s
sys     0m0.071s

With the fix:

# time /tmp/repro
Test passed, all good
Terminated

real    1m1.286s
user    0m0.004s
sys     0m0.970s



Pasha

View attachment "repro.c" of type "text/x-csrc" (2440 bytes)