From patchwork Wed Dec 27 05:43:54 2017
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Subject: x86/cpu, x86/pti: Do not enable PTI on AMD processors
From: Tom Lendacky <thomas.lendacky@amd.com>
X-Patchwork-Id: 10133447
Message-Id: <20171227054354.20369.94587.stgit@tlendack-t1.amdoffice.net>
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>
Date: Tue, 26 Dec 2017 23:43:54 -0600

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>
Reviewed-by: Borislav Petkov <bp@suse.de>
---
 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);