From: Will Deacon <will@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 1/2] arm64: Add initial support for E0PD
Date: Tue, 13 Aug 2019 18:25:33 +0100 [thread overview]
Message-ID: <20190813172532.hid5cmzhrq7s742l@willie-the-truck> (raw)
In-Reply-To: <20190812125738.17388-2-broonie@kernel.org>
On Mon, Aug 12, 2019 at 01:57:37PM +0100, Mark Brown wrote:
> Kernel Page Table Isolation (KPTI) is used to mitigate some speculation
> based security issues by ensuring that the kernel is not mapped when
> userspace is running but this approach is expensive and is incompatible
> with SPE. E0PD, introduced in the ARMv8.5 extensions, provides an
> alternative to this which ensures that accesses from userspace to the
> kernel's half of the memory map to always fault with constant time,
> preventing timing attacks without requiring constant unmapping and
> remapping or preventing legitimate accesses.
>
> This initial patch does not yet integrate with KPTI, this will be dealt
> with in followup patches. Ideally we could ensure that by default we
> don't use KPTI on CPUs where E0PD is present.
>
> Signed-off-by: Mark Brown <broonie@kernel.org>
> ---
> arch/arm64/Kconfig | 14 +++++++++++++
> arch/arm64/include/asm/cpucaps.h | 3 ++-
> arch/arm64/include/asm/pgtable-hwdef.h | 2 ++
> arch/arm64/include/asm/sysreg.h | 1 +
> arch/arm64/kernel/cpufeature.c | 27 ++++++++++++++++++++++++++
> 5 files changed, 46 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index c6a978b0fb7c..3a6875a5bb99 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1409,6 +1409,20 @@ config ARM64_PTR_AUTH
>
> endmenu
>
> +menu "ARMv8.5 architectural features"
> +
> +config ARM64_E0PD
> + bool "Enable support for E0PD"
> + default y
> + help
> + E0PD (part of the ARMv8.5 extensions) ensures that EL0
> + accesses made via TTBR1 always fault in constant time,
> + providing the same guarantees as KPTI with lower overhead.
This could do with a slight tweak, since there are two E0PD bits in the
TCR, which apply to TTBR0 and TTBR1 separately. I'd also be reluctant
to state that it provides the /same/ guarantees as kpti, since I don't
think it will cause a translation fault.
It's probably also worth mentioning that, unlike kpti, E0PDx doesn't
break profiling with SPE.
> + This option enables E0PD where available.
For TTBR1.
Will
_______________________________________________
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:[~2019-08-13 17:25 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 12:57 [0/2] arm64: E0PD support Mark Brown
2019-08-12 12:57 ` [PATCH 1/2] arm64: Add initial support for E0PD Mark Brown
2019-08-13 9:59 ` Suzuki K Poulose
2019-08-13 17:25 ` Will Deacon [this message]
2019-08-12 12:57 ` [PATCH 2/2] arm64: Don't use KPTI where we have E0PD Mark Brown
2019-08-13 10:01 ` Suzuki K Poulose
2019-08-13 17:28 ` Will Deacon
2019-08-13 19:05 ` Mark Brown
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190813172532.hid5cmzhrq7s742l@willie-the-truck \
--to=will@kernel.org \
--cc=broonie@kernel.org \
--cc=catalin.marinas@arm.com \
--cc=linux-arm-kernel@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).