Add warning when `nx_huge_pages` is enabled by `auto` for hint that huge pages may be splited by kernel. Add warning when CVE-2018-12207 may arise but `nx_huge_pages` is disabled for hint that malicious guest may cause a CPU lookup. Signed-off-by: Li Yu <liyu.yukiteru@xxxxxxxxxxxxx> --- arch/x86/kvm/mmu/mmu.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 1a64ba5b9437..32026592e566 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -6056,19 +6056,26 @@ static void __set_nx_huge_pages(bool val) nx_huge_pages = itlb_multihit_kvm_mitigation = val; } +#define ITLB_MULTIHIT_NX_ON "iTLB multi-hit CPU bug present and cpu mitigations enabled, huge pages may be splited by kernel for security. See CVE-2018-12207 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/multihit.html for details.\n" +#define ITLB_MULTIHIT_NX_OFF "iTLB multi-hit CPU bug present and cpu mitigations enabled, malicious guest may cause a CPU lookup. See CVE-2018-12207 and https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/multihit.html for details.\n" + static int set_nx_huge_pages(const char *val, const struct kernel_param *kp) { bool old_val = nx_huge_pages; bool new_val; /* In "auto" mode deploy workaround only if CPU has the bug. */ - if (sysfs_streq(val, "off")) + if (sysfs_streq(val, "off")) { new_val = 0; - else if (sysfs_streq(val, "force")) + if (get_nx_auto_mode() && new_val != old_val) + pr_warn(ITLB_MULTIHIT_NX_OFF); + } else if (sysfs_streq(val, "force")) new_val = 1; - else if (sysfs_streq(val, "auto")) + else if (sysfs_streq(val, "auto")) { new_val = get_nx_auto_mode(); - else if (strtobool(val, &new_val) < 0) + if (new_val && new_val != old_val) + pr_warn(ITLB_MULTIHIT_NX_ON); + } else if (strtobool(val, &new_val) < 0) return -EINVAL; __set_nx_huge_pages(new_val); @@ -6095,8 +6102,11 @@ int kvm_mmu_module_init(void) { int ret = -ENOMEM; - if (nx_huge_pages == -1) + if (nx_huge_pages == -1) { __set_nx_huge_pages(get_nx_auto_mode()); + if (is_nx_huge_page_enabled()) + pr_warn_once(ITLB_MULTIHIT_NX_ON); + } /* * MMU roles use union aliasing which is, generally speaking, an -- 2.11.0
