From: Brian Gerst <brgerst@gmail.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: Tom Lendacky <thomas.lendacky@amd.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@suse.de>
Subject: Re: [PATCH] x86/cpu, x86/pti: Do not enable PTI on AMD processors
Date: Mon, 12 Feb 2018 10:37:36 -0500 [thread overview]
Message-ID: <CAMzpN2gRtzyHZ8Pt3T55_tP+uRxe47x-OqveA7Gda4M3Lb87Gw@mail.gmail.com> (raw)
In-Reply-To: <20180212152630.GD13962@amd>
On Mon, Feb 12, 2018 at 10:26 AM, Pavel Machek <pavel@ucw.cz> wrote:
> On Tue 2017-12-26 23:43:54, Tom Lendacky wrote:
>> AMD processors are not subject to the types of attacks that the kernel
>> page table isolation feature protects against. The AMD microarchitecture
>> does not allow memory references, including speculative references, that
>> access higher privileged data when running in a lesser privileged mode
>> when that access would result in a page fault.
>>
>> Disable page table isolation by default on AMD processors by not setting
>> the X86_BUG_CPU_INSECURE feature, which controls whether X86_FEATURE_PTI
>> is set.
>
> PTI was originally meant to protect KASLR from memory leaks, before
> Spectre was public. I guess that's still valid use on AMD cpus?
> Pavel
KASLR leaks are a much lower threat than Meltdown. Given that no AMD
processor supports PCID, enabling PTI has a much more significant
performance impact for a much smaller benefit. For the paranoid user
they still have the option to enable PTI at boot, but it should not be
on by default.
--
Brian Gerst
next prev parent reply other threads:[~2018-02-12 15:37 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-27 5:43 [PATCH] x86/cpu, x86/pti: Do not enable PTI on AMD processors Tom Lendacky
2017-12-27 8:48 ` Dave Hansen
2017-12-27 14:47 ` Tom Lendacky
2017-12-28 0:20 ` Borislav Petkov
2018-01-03 16:21 ` [tip:x86/pti] " tip-bot for Tom Lendacky
2018-02-12 15:26 ` [PATCH] " Pavel Machek
2018-02-12 15:37 ` Brian Gerst [this message]
2018-02-13 13:21 ` Thomas Gleixner
2018-01-03 11:07 Ivan Ivanov
2018-01-03 19:38 Tim Mouraveiko
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