4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Tom Lendacky thomas.lendacky@amd.com
commit 694d99d40972f12e59a3696effee8a376b79d7c8 upstream.
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.amdof... Cc: Nick Lowe nick.lowe@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kernel/cpu/common.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -831,8 +831,8 @@ static void __init early_identify_cpu(st
setup_force_cpu_cap(X86_FEATURE_ALWAYS);
- /* Assume for now that ALL x86 CPUs are insecure */ - setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN); + if (c->x86_vendor != X86_VENDOR_AMD) + setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
setup_force_cpu_bug(X86_BUG_SPECTRE_V1); setup_force_cpu_bug(X86_BUG_SPECTRE_V2);