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
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com> To: Luis Machado <luis.machado@linaro.org> Cc: Kevin Brodsky <kevin.brodsky@arm.com>, stable@vger.kernel.org, Steven Price <steven.price@arm.com>, David Spickett <david.spickett@linaro.org>, Vincenzo Frascino <vincenzo.frascino@arm.com>, Will Deacon <will@kernel.org>, linux-arm-kernel@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-02-11 10:38 UTC|newest] Thread overview: 11+ 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 18:03 ` Catalin Marinas 2021-02-10 18:52 ` Luis Machado 2021-02-10 18:52 ` Luis Machado 2021-02-11 10:35 ` Catalin Marinas [this message] 2021-02-11 10:35 ` Catalin Marinas 2021-02-11 10:56 ` Vincenzo Frascino 2021-02-11 10:56 ` Vincenzo Frascino 2021-02-12 16:45 ` Catalin Marinas 2021-02-12 16:45 ` Catalin Marinas 2021-02-16 18:56 vivek
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