From e2c87b1ba04bd5042f6db0780ed55abaf4836378 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Wed, 13 Nov 2019 21:05:44 +1100 Subject: KVM: PPC: Book3S HV: Flush link stack on guest exit to host kernel commit af2e8c68b9c5403f77096969c516f742f5bb29e0 upstream. On some systems that are vulnerable to Spectre v2, it is up to software to flush the link stack (return address stack), in order to protect against Spectre-RSB. When exiting from a guest we do some house keeping and then potentially exit to C code which is several stack frames deep in the host kernel. We will then execute a series of returns without preceeding calls, opening up the possiblity that the guest could have poisoned the link stack, and direct speculative execution of the host to a gadget of some sort. To prevent this we add a flush of the link stack on exit from a guest. Signed-off-by: Michael Ellerman [dja: straightforward backport to v4.14] Signed-off-by: Daniel Axtens Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/kernel/security.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'arch/powerpc/kernel') diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c index 07e066a2f5b7..11fff9669cfd 100644 --- a/arch/powerpc/kernel/security.c +++ b/arch/powerpc/kernel/security.c @@ -393,6 +393,9 @@ static void toggle_count_cache_flush(bool enable) if (!enable) { patch_instruction_site(&patch__call_flush_count_cache, PPC_INST_NOP); +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE + patch_instruction_site(&patch__call_kvm_flush_link_stack, PPC_INST_NOP); +#endif pr_info("link-stack-flush: software flush disabled.\n"); link_stack_flush_enabled = false; no_count_cache_flush(); @@ -403,6 +406,12 @@ static void toggle_count_cache_flush(bool enable) patch_branch_site(&patch__call_flush_count_cache, (u64)&flush_count_cache, BRANCH_SET_LINK); +#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE + // This enables the branch from guest_exit_cont to kvm_flush_link_stack + patch_branch_site(&patch__call_kvm_flush_link_stack, + (u64)&kvm_flush_link_stack, BRANCH_SET_LINK); +#endif + pr_info("link-stack-flush: software flush enabled.\n"); link_stack_flush_enabled = true; -- cgit v1.2.3