From: Catalin Marinas <catalin.marinas@arm.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org, maz@kernel.org,
will@kernel.org, mark.rutland@arm.com, anshuman.khandual@arm.com,
qperret@google.com, kernel-team@android.com
Subject: Re: [PATCH 2/2] arm64: mm: use XN table mapping attributes for the linear region
Date: Fri, 5 Mar 2021 19:06:00 +0000 [thread overview]
Message-ID: <20210305190600.GK23855@arm.com> (raw)
In-Reply-To: <20210304171145.12281-3-ardb@kernel.org>
On Thu, Mar 04, 2021 at 06:11:45PM +0100, Ard Biesheuvel wrote:
> The way the arm64 kernel virtual address space is constructed guarantees
> that swapper PGD entries are never shared between the linear region on
> the one hand, and the vmalloc region on the other, which is where all
> kernel text, module text and BPF text mappings reside.
>
> This means that mappings in the linear region (which never require
> executable permissions) never share any table entries at any level with
> mappings that do require executable permissions, and so we can set the
> table-level PXN/UXN attributes for all table entries that are created
> while setting up mappings in the linear region. Since swapper's PGD
> level page table is mapped r/o itself, this adds another layer of
> robustness to the way the kernel manages its own page tables.
In ARMv8.1 the architecture added the possibility of disabling the
hierarchical page table permissions (FEAT_HPDS) so that we can use these
bits for software.
Is there any big advantage to using the hierarchical permissions vs
some sanity check in set_pte() for example?
--
Catalin
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next prev parent reply other threads:[~2021-03-05 19:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-04 17:11 [PATCH 0/2] arm64: use XN table mappings for the linear region Ard Biesheuvel
2021-03-04 17:11 ` [PATCH 1/2] arm64: mm: add missing P4D definitions and use them consistently Ard Biesheuvel
2021-03-04 17:39 ` Mark Rutland
2021-03-08 9:06 ` Anshuman Khandual
2021-03-08 9:07 ` Ard Biesheuvel
2021-03-04 17:11 ` [PATCH 2/2] arm64: mm: use XN table mapping attributes for the linear region Ard Biesheuvel
2021-03-04 17:39 ` Mark Rutland
2021-03-05 8:13 ` Ard Biesheuvel
2021-03-05 19:06 ` Catalin Marinas [this message]
2021-03-05 19:17 ` Ard Biesheuvel
2021-03-05 20:37 ` Catalin Marinas
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