From: Catalin Marinas <catalin.marinas@arm.com>
To: Luis Machado <luis.machado@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org,
Kevin Brodsky <kevin.brodsky@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Steven Price <steven.price@arm.com>,
stable@vger.kernel.org, Will Deacon <will@kernel.org>,
David Spickett <david.spickett@linaro.org>
Subject: Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
Date: Thu, 11 Feb 2021 10:35:29 +0000 [thread overview]
Message-ID: <20210211103528.GA12106@arm.com> (raw)
In-Reply-To: <0916e89e-46b5-6002-7f9d-5d1df9e3e205@linaro.org>
On Wed, Feb 10, 2021 at 03:52:18PM -0300, Luis Machado wrote:
> On 2/10/21 3:03 PM, Catalin Marinas wrote:
> > The ptrace(PTRACE_PEEKMTETAGS) implementation checks whether the user
> > page has valid tags (mapped with PROT_MTE) by testing the PG_mte_tagged
> > page flag. If this bit is cleared, ptrace(PTRACE_PEEKMTETAGS) returns
> > -EIO.
> >
> > A newly created (PROT_MTE) mapping points to the zero page which had its
> > tags zeroed during cpu_enable_mte(). If there were no prior writes to
> > this mapping, ptrace(PTRACE_PEEKMTETAGS) fails with -EIO since the zero
> > page does not have the PG_mte_tagged flag set.
> >
> > Set PG_mte_tagged on the zero page when its tags are cleared during
> > boot. In addition, to avoid ptrace(PTRACE_PEEKMTETAGS) succeeding on
> > !PROT_MTE mappings pointing to the zero page, change the
> > __access_remote_tags() check to (vm_flags & VM_MTE) instead of
> > PG_mte_tagged.
> >
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE")
> > Cc: <stable@vger.kernel.org> # 5.10.x
> > Cc: Will Deacon <will@kernel.org>
> > Reported-by: Luis Machado <luis.machado@linaro.org>
[...]
> Thanks. I gave this a try and it works as expected. So memory that is
> PROT_MTE but has not been accessed yet can be inspected with PEEKMTETAGS
> without getting an EIO back.
Thanks. I assume I can add your tested-by.
--
Catalin
next prev parent reply other threads:[~2021-02-11 10:38 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-10 18:03 [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Catalin Marinas
2021-02-10 18:52 ` Luis Machado
2021-02-11 10:35 ` Catalin Marinas [this message]
2021-02-11 10:56 ` Vincenzo Frascino
2021-02-12 16:45 ` Catalin Marinas
2021-02-16 18:56 vivek
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