Merge tag 's390-5.2-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

[linux-2.6-microblaze.git] / arch / x86 / include / asm / mmu_context.h

diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 19d18fa..93dff19 100644 (file)
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -13,6 +13,7 @@
 #include <asm/tlbflush.h>
 #include <asm/paravirt.h>
 #include <asm/mpx.h>
+#include <asm/debugreg.h>
 
 extern atomic64_t last_mm_ctx_id;
 
@@ -356,4 +357,59 @@ static inline unsigned long __get_current_cr3_fast(void)
        return cr3;
 }
 
+typedef struct {
+       struct mm_struct *mm;
+} temp_mm_state_t;
+
+/*
+ * Using a temporary mm allows to set temporary mappings that are not accessible
+ * by other CPUs. Such mappings are needed to perform sensitive memory writes
+ * that override the kernel memory protections (e.g., W^X), without exposing the
+ * temporary page-table mappings that are required for these write operations to
+ * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the
+ * mapping is torn down.
+ *
+ * Context: The temporary mm needs to be used exclusively by a single core. To
+ *          harden security IRQs must be disabled while the temporary mm is
+ *          loaded, thereby preventing interrupt handler bugs from overriding
+ *          the kernel memory protection.
+ */
+static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
+{
+       temp_mm_state_t temp_state;
+
+       lockdep_assert_irqs_disabled();
+       temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
+       switch_mm_irqs_off(NULL, mm, current);
+
+       /*
+        * If breakpoints are enabled, disable them while the temporary mm is
+        * used. Userspace might set up watchpoints on addresses that are used
+        * in the temporary mm, which would lead to wrong signals being sent or
+        * crashes.
+        *
+        * Note that breakpoints are not disabled selectively, which also causes
+        * kernel breakpoints (e.g., perf's) to be disabled. This might be
+        * undesirable, but still seems reasonable as the code that runs in the
+        * temporary mm should be short.
+        */
+       if (hw_breakpoint_active())
+               hw_breakpoint_disable();
+
+       return temp_state;
+}
+
+static inline void unuse_temporary_mm(temp_mm_state_t prev_state)
+{
+       lockdep_assert_irqs_disabled();
+       switch_mm_irqs_off(NULL, prev_state.mm, current);
+
+       /*
+        * Restore the breakpoints if they were disabled before the temporary mm
+        * was loaded.
+        */
+       if (hw_breakpoint_active())
+               hw_breakpoint_restore();
+}
+
 #endif /* _ASM_X86_MMU_CONTEXT_H */