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From: Catalin Marinas <catalin.marinas@arm.com>
To: Guo Ren <guoren@kernel.org>
Cc: Julien Grall <julien.grall@arm.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	kvmarm@lists.cs.columbia.edu, aou@eecs.berkeley.edu,
	gary@garyguo.net, Atish Patra <Atish.Patra@wdc.com>,
	hch@infradead.org, paul.walmsley@sifive.com, rppt@linux.ibm.com,
	linux-riscv@lists.infradead.org, Anup Patel <anup.Patel@wdc.com>,
	Palmer Dabbelt <palmer@sifive.com>,
	suzuki.poulose@arm.com, Marc Zyngier <marc.zyngier@arm.com>,
	julien.thierry@arm.com, Will Deacon <will.deacon@arm.com>,
	christoffer.dall@arm.com, james.morse@arm.com,
	linux-csky@vger.kernel.org
Subject: Re: [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file
Date: Mon, 22 Jul 2019 17:38:12 +0100	[thread overview]
Message-ID: <20190722163811.GJ60625@arrakis.emea.arm.com> (raw)
In-Reply-To: <CAJF2gTTEbhA-pZCPGuUNqXT9F-vk8fSTyNJyEOpn=QE=toAN3g@mail.gmail.com>

On Tue, Jul 16, 2019 at 11:31:27AM +0800, Guo Ren wrote:
> I saw arm64 to prevent speculation by temporarily setting TTBR0.el1 to
> a zero page table. Is that used to prevent speculative execution user
> space code or just prevent ld/st in copy_use_* ?

Only to prevent explicit ld/st from user. On ARMv8.1+, we don't normally
use the TTBR0 trick but rather disable user space access using the PAN
(privileged access never) feature. However, I don't think PAN disables
speculative accesses, only explicit loads/stores. Also, with ARMv8.2
Linux uses the LDTR/STTR instructions in copy_*_user() which don't need
to disable PAN explicitly.

-- 
Catalin

      reply	other threads:[~2019-07-22 16:38 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20190321163623.20219-1-julien.grall@arm.com>
     [not found] ` <20190321163623.20219-12-julien.grall@arm.com>
     [not found]   ` <0dfe120b-066a-2ac8-13bc-3f5a29e2caa3@arm.com>
     [not found]     ` <CAJF2gTTXHHgDboaexdHA284y6kNZVSjLis5-Q2rDnXCxr4RSmA@mail.gmail.com>
     [not found]       ` <c871a5ae-914f-a8bb-9474-1dcfec5d45bf@arm.com>
     [not found]         ` <CAJF2gTStSR7Jmu7=HaO5Wxz=Zn8A5-RD8ktori3oKEhM9vozAA@mail.gmail.com>
     [not found]           ` <20190621141606.GF18954@arrakis.emea.arm.com>
     [not found]             ` <CAJF2gTTVUToRkRtxTmtWDotMGXy5YQCpL1h_2neTBuN3e6oz1w@mail.gmail.com>
     [not found]               ` <20190624153820.GH29120@arrakis.emea.arm.com>
     [not found]                 ` <CAJF2gTRUzHUNV+nzECUp5n2L1akdy=Aovb6tSd+PNVnpasBrqw@mail.gmail.com>
     [not found]                   ` <20190701091711.GA21774@arrakis.emea.arm.com>
2019-07-16  3:31                     ` [PATCH RFC 11/14] arm64: Move the ASID allocator code in a separate file Guo Ren
2019-07-22 16:38                       ` Catalin Marinas [this message]

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