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Diffstat (limited to 'arch/x86/mm/pti.c')
-rw-r--r--arch/x86/mm/pti.c126
1 files changed, 121 insertions, 5 deletions
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index 631507f0c198..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;
@@ -300,6 +315,27 @@ pti_clone_pmds(unsigned long start, unsigned long end, pmdval_t clear)
return;
/*
+ * Only clone present PMDs. This ensures only setting
+ * _PAGE_GLOBAL on present PMDs. This should only be
+ * called on well-known addresses anyway, so a non-
+ * present PMD would be a surprise.
+ */
+ if (WARN_ON(!(pmd_flags(*pmd) & _PAGE_PRESENT)))
+ return;
+
+ /*
+ * Setting 'target_pmd' below creates a mapping in both
+ * the user and kernel page tables. It is effectively
+ * global, so set it as global in both copies. Note:
+ * the X86_FEATURE_PGE check is not _required_ because
+ * the CPU ignores _PAGE_GLOBAL when PGE is not
+ * supported. The check keeps consistentency with
+ * code that only set this bit when supported.
+ */
+ if (boot_cpu_has(X86_FEATURE_PGE))
+ *pmd = pmd_set_flags(*pmd, _PAGE_GLOBAL);
+
+ /*
* Copy the PMD. That is, the kernelmode and usermode
* tables will share the last-level page tables of this
* address range
@@ -348,7 +384,83 @@ static void __init pti_clone_entry_text(void)
{
pti_clone_pmds((unsigned long) __entry_text_start,
(unsigned long) __irqentry_text_end,
- _PAGE_RW | _PAGE_GLOBAL);
+ _PAGE_RW);
+}
+
+/*
+ * 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.
+ */
+extern int set_memory_nonglobal(unsigned long addr, int numpages);
+void pti_set_kernel_image_nonglobal(void)
+{
+ /*
+ * The identity map is created with PMDs, regardless of the
+ * actual length of the kernel. We need to clear
+ * _PAGE_GLOBAL up to a PMD boundary, not just to the end
+ * of the image.
+ */
+ 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);
}
/*
@@ -362,6 +474,10 @@ void __init pti_init(void)
pr_info("enabled\n");
pti_clone_user_shared();
+
+ /* Undo all global bits from the init pagetables in head_64.S: */
+ pti_set_kernel_image_nonglobal();
+ /* Replace some of the global bits just for shared entry text: */
pti_clone_entry_text();
pti_setup_espfix64();
pti_setup_vsyscall();