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From: Tom Lendacky <thomas.lendacky@amd.com>
To: x86@kernel.org
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
	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: [PATCH] x86/cpu, x86/pti: Do not enable PTI on AMD processors
Date: Tue, 26 Dec 2017 23:43:54 -0600
Message-ID: <20171227054354.20369.94587.stgit@tlendack-t1.amdoffice.net> (raw)

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.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/kernel/cpu/common.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index c47de4e..7d9e3b0 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -923,8 +923,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 
 	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
 
-	/* Assume for now that ALL x86 CPUs are insecure */
-	setup_force_cpu_bug(X86_BUG_CPU_INSECURE);
+	if (c->x86_vendor != X86_VENDOR_AMD)
+		setup_force_cpu_bug(X86_BUG_CPU_INSECURE);
 
 	fpu__init_system(c);
 

             reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-27  5:43 Tom Lendacky [this message]
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
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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