diff options
| author | Michael Ellerman <mpe@ellerman.id.au> | 2019-11-13 21:05:44 +1100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-11-28 18:29:06 +0100 |
| commit | e2c87b1ba04bd5042f6db0780ed55abaf4836378 (patch) | |
| tree | 88965b270ad14fa8f84bff3973f2f8c913f06132 /arch/powerpc/kernel | |
| parent | 113408cdaec11a6e34d4edabb134a335dd4896b3 (diff) | |
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 <mpe@ellerman.id.au>
[dja: straightforward backport to v4.14]
Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/powerpc/kernel')
| -rw-r--r-- | arch/powerpc/kernel/security.c | 9 |
1 files changed, 9 insertions, 0 deletions
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; |