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

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index f2a94dfb434e9a7c61d6eacc28dd0129f6e844e1..b1be494ab4e8badf1bb225e34a7a7e4203af6de4 100644 (file)
--- 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);