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authorMichael Ellerman <mpe@ellerman.id.au>2019-11-13 21:05:44 +1100
committerMichael Ellerman <mpe@ellerman.id.au>2019-11-14 15:37:59 +1100
commitaf2e8c68b9c5403f77096969c516f742f5bb29e0 (patch)
tree57edfd525c9dc14dac4921dff158a611be3f4a9f /arch/powerpc/kernel/security.c
parent39e72bf96f5847ba87cc5bd7a3ce0fed813dc9ad (diff)
KVM: PPC: Book3S HV: Flush link stack on guest exit to host kernel
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 <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/security.c')
-rw-r--r--arch/powerpc/kernel/security.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/security.c b/arch/powerpc/kernel/security.c
index a3138e7d71bb..bd91dceb7010 100644
--- a/arch/powerpc/kernel/security.c
+++ b/arch/powerpc/kernel/security.c
@@ -400,6 +400,9 @@ 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();
@@ -410,6 +413,12 @@ 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;