diff options
Diffstat (limited to 'arch/x86/mm/pti.c')
| -rw-r--r-- | arch/x86/mm/pti.c | 78 |
1 files changed, 74 insertions, 4 deletions
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c index 1470b173963f..f1fd52f449e0 100644 --- a/arch/x86/mm/pti.c +++ b/arch/x86/mm/pti.c @@ -66,12 +66,22 @@ static void __init pti_print_if_secure(const char *reason) pr_info("%s\n", reason); } +enum pti_mode { + PTI_AUTO = 0, + PTI_FORCE_OFF, + PTI_FORCE_ON +} pti_mode; + void __init pti_check_boottime_disable(void) { char arg[5]; int ret; + /* Assume mode is auto unless overridden. */ + pti_mode = PTI_AUTO; + if (hypervisor_is_type(X86_HYPER_XEN_PV)) { + pti_mode = PTI_FORCE_OFF; pti_print_if_insecure("disabled on XEN PV."); return; } @@ -79,18 +89,23 @@ void __init pti_check_boottime_disable(void) ret = cmdline_find_option(boot_command_line, "pti", arg, sizeof(arg)); if (ret > 0) { if (ret == 3 && !strncmp(arg, "off", 3)) { + pti_mode = PTI_FORCE_OFF; pti_print_if_insecure("disabled on command line."); return; } if (ret == 2 && !strncmp(arg, "on", 2)) { + pti_mode = PTI_FORCE_ON; pti_print_if_secure("force enabled on command line."); goto enable; } - if (ret == 4 && !strncmp(arg, "auto", 4)) + if (ret == 4 && !strncmp(arg, "auto", 4)) { + pti_mode = PTI_AUTO; goto autosel; + } } if (cmdline_find_option_bool(boot_command_line, "nopti")) { + pti_mode = PTI_FORCE_OFF; pti_print_if_insecure("disabled on command line."); return; } @@ -149,7 +164,7 @@ pgd_t __pti_set_user_pgd(pgd_t *pgdp, pgd_t pgd) * * Returns a pointer to a P4D on success, or NULL on failure. */ -static __init p4d_t *pti_user_pagetable_walk_p4d(unsigned long address) +static p4d_t *pti_user_pagetable_walk_p4d(unsigned long address) { pgd_t *pgd = kernel_to_user_pgdp(pgd_offset_k(address)); gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); @@ -177,7 +192,7 @@ static __init p4d_t *pti_user_pagetable_walk_p4d(unsigned long address) * * Returns a pointer to a PMD on success, or NULL on failure. */ -static __init pmd_t *pti_user_pagetable_walk_pmd(unsigned long address) +static pmd_t *pti_user_pagetable_walk_pmd(unsigned long address) { gfp_t gfp = (GFP_KERNEL | __GFP_NOTRACK | __GFP_ZERO); p4d_t *p4d = pti_user_pagetable_walk_p4d(address); @@ -267,7 +282,7 @@ static void __init pti_setup_vsyscall(void) static void __init pti_setup_vsyscall(void) { } #endif -static void __init +static void pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear) { unsigned long addr; @@ -373,6 +388,58 @@ static void __init pti_clone_entry_text(void) } /* + * Global pages and PCIDs are both ways to make kernel TLB entries + * live longer, reduce TLB misses and improve kernel performance. + * But, leaving all kernel text Global makes it potentially accessible + * to Meltdown-style attacks which make it trivial to find gadgets or + * defeat KASLR. + * + * Only use global pages when it is really worth it. + */ +static inline bool pti_kernel_image_global_ok(void) +{ + /* + * Systems with PCIDs get litlle benefit from global + * kernel text and are not worth the downsides. + */ + if (cpu_feature_enabled(X86_FEATURE_PCID)) + return false; + + /* + * Only do global kernel image for pti=auto. Do the most + * secure thing (not global) if pti=on specified. + */ + if (pti_mode != PTI_AUTO) + return false; + + /* + * K8 may not tolerate the cleared _PAGE_RW on the userspace + * global kernel image pages. Do the safe thing (disable + * global kernel image). This is unlikely to ever be + * noticed because PTI is disabled by default on AMD CPUs. + */ + if (boot_cpu_has(X86_FEATURE_K8)) + return false; + + return true; +} + +/* + * For some configurations, map all of kernel text into the user page + * tables. This reduces TLB misses, especially on non-PCID systems. + */ +void pti_clone_kernel_text(void) +{ + unsigned long start = PFN_ALIGN(_text); + unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE); + + if (!pti_kernel_image_global_ok()) + return; + + pti_clone_pmds(start, end, _PAGE_RW); +} + +/* * This is the only user for it and it is not arch-generic like * the other set_memory.h functions. Just extern it. */ @@ -388,6 +455,9 @@ void pti_set_kernel_image_nonglobal(void) unsigned long start = PFN_ALIGN(_text); unsigned long end = ALIGN((unsigned long)_end, PMD_PAGE_SIZE); + if (pti_kernel_image_global_ok()) + return; + pr_debug("set kernel image non-global\n"); set_memory_nonglobal(start, (end - start) >> PAGE_SHIFT); |