[tip:x86/pti] x86/cpu, x86/pti: Do not enable PTI on AMD processors

[tip-bot for Tom Lendacky <tipbot@zytor.com>]

Commit-ID:  694d99d40972f12e59a3696effee8a376b79d7c8
Gitweb:     https://git.kernel.org/tip/694d99d40972f12e59a3696effee8a376b79d7c8
Author:     Tom Lendacky <thomas.lendacky@amd.com>
AuthorDate: Tue, 26 Dec 2017 23:43:54 -0600
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Wed, 3 Jan 2018 15:57:59 +0100

x86/cpu, x86/pti: Do not enable PTI on AMD processors

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>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20171227054354.20369.94587.stgit@tlendack-t1.amdoffice.net

---
 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 f2a94df..b1be494 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -899,8 +899,8 @@ 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);