From: Steven Price <steven.price@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org
Cc: linux-arch@vger.kernel.org,
Richard Earnshaw <Richard.Earnshaw@arm.com>,
Will Deacon <will@kernel.org>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
linux-mm@kvack.org, Vincenzo Frascino <vincenzo.frascino@arm.com>,
Peter Collingbourne <pcc@google.com>
Subject: Re: [PATCH v2 04/19] arm64: mte: Use Normal Tagged attributes for the linear map
Date: Thu, 5 Mar 2020 16:21:34 +0000 [thread overview]
Message-ID: <946fcd05-ba8f-90ec-d30b-458b327df59c@arm.com> (raw)
In-Reply-To: <20200226180526.3272848-5-catalin.marinas@arm.com>
On 26/02/2020 18:05, Catalin Marinas wrote:
> Once user space is given access to tagged memory, the kernel must be
> able to clear/save/restore tags visible to the user. This is done via
> the linear mapping, therefore map it as such. The new MT_NORMAL_TAGGED
> index for MAIR_EL1 is initially mapped as Normal memory and later
> changed to Normal Tagged via the cpufeature infrastructure. From a
> mismatched attribute aliases perspective, the Tagged memory is
> considered a permission and it won't lead to undefined behaviour.
>
> The empty_zero_page is cleared to ensure that the tags it contains are
> already zeroed. The actual tags-aware clear_page() implementation is
> part of a subsequent patch.
>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> ---
> arch/arm64/include/asm/memory.h | 1 +
> arch/arm64/include/asm/pgtable-prot.h | 2 ++
> arch/arm64/kernel/cpufeature.c | 30 +++++++++++++++++++++++++++
> arch/arm64/mm/dump.c | 4 ++++
> arch/arm64/mm/mmu.c | 22 ++++++++++++++++++--
> arch/arm64/mm/proc.S | 8 +++++--
> 6 files changed, 63 insertions(+), 4 deletions(-)
>
[...]
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 128f70852bf3..a2c206444e47 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -120,7 +120,7 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> * The following mapping attributes may be updated in live
> * kernel mappings without the need for break-before-make.
> */
> - static const pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
> + pteval_t mask = PTE_PXN | PTE_RDONLY | PTE_WRITE | PTE_NG;
>
> /* creating or taking down mappings is always safe */
> if (old == 0 || new == 0)
> @@ -134,6 +134,19 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
> if (old & ~new & PTE_NG)
> return false;
>
> + if (system_supports_mte()) {
> + /*
> + * Changing the memory type between Normal and Normal-Tagged
> + * is safe since Tagged is considered a permission attribute
> + * from the mismatched attribute aliases perspective.
> + */
> + if ((old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL) ||
> + (old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL_TAGGED) ||
> + (new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL) ||
> + (new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL_TAGGED))
> + mask |= PTE_ATTRINDX_MASK;
> + }
> +
> return ((old ^ new) & ~mask) == 0;
> }
This is much more permissive than I would expect. If either the old or
new memory type is NORMAL (or NORMAL_TAGGED) then the memory type is
ignored altogether.
Should this check be:
if (((old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL) ||
(old & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL_TAGGED)) &&
((new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL) ||
(new & PTE_ATTRINDX_MASK) == PTE_ATTRINDX(MT_NORMAL_TAGGED)))
Steve
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next prev parent reply other threads:[~2020-03-05 16:21 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 18:05 [PATCH v2 00/19] arm64: Memory Tagging Extension user-space support Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 01/19] arm64: alternative: Allow alternative_insn to always issue the first instruction Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 02/19] arm64: mte: system register definitions Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 03/19] arm64: mte: CPU feature detection and initial sysreg configuration Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 04/19] arm64: mte: Use Normal Tagged attributes for the linear map Catalin Marinas
2020-03-05 16:21 ` Steven Price [this message]
2020-03-05 16:38 ` Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 05/19] arm64: mte: Assembler macros and default architecture for .S files Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 06/19] arm64: mte: Tags-aware clear_page() implementation Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 07/19] arm64: mte: Tags-aware copy_page() implementation Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 08/19] arm64: Tags-aware memcmp_pages() implementation Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 09/19] arm64: mte: Add specific SIGSEGV codes Catalin Marinas
2020-02-26 19:05 ` Eric W. Biederman
2020-02-26 19:26 ` Catalin Marinas
2020-02-26 22:33 ` kbuild test robot
2020-02-27 11:05 ` Catalin Marinas
2020-02-27 15:20 ` Eric W. Biederman
2020-02-26 18:05 ` [PATCH v2 10/19] arm64: mte: Handle synchronous and asynchronous tag check faults Catalin Marinas
2020-02-27 11:50 ` Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 11/19] mm: Introduce arch_calc_vm_flag_bits() Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 12/19] arm64: mte: Add PROT_MTE support to mmap() and mprotect() Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 13/19] mm: Introduce arch_validate_flags() Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 14/19] arm64: mte: Validate the PROT_MTE request via arch_validate_flags() Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 15/19] mm: Allow arm64 mmap(PROT_MTE) on RAM-based files Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 16/19] arm64: mte: Allow user control of the tag check mode via prctl() Catalin Marinas
2020-03-09 13:53 ` Kevin Brodsky
2020-02-26 18:05 ` [PATCH v2 17/19] arm64: mte: Allow user control of the generated random tags " Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 18/19] arm64: mte: Kconfig entry Catalin Marinas
2020-02-26 18:05 ` [PATCH v2 19/19] arm64: mte: Add Memory Tagging Extension documentation Catalin Marinas
2020-03-09 14:30 ` Kevin Brodsky
2020-03-11 22:17 ` Richard Henderson
2020-03-12 9:50 ` Catalin Marinas
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