1 files changed, 67 insertions, 14 deletions

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 7867dfb3963e..8fd39ff74a49 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -18,7 +18,6 @@
 #include <asm/text-patching.h>
 #include <asm/alternative.h>
 #include <asm/sections.h>
-#include <asm/pgtable.h>
 #include <asm/mce.h>
 #include <asm/nmi.h>
 #include <asm/cacheflush.h>
@@ -783,6 +782,61 @@ void __init_or_module text_poke_early(void *addr, const void *opcode,
 	}
 }
 
+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();
+}
+
 __ro_after_init struct mm_struct *poking_mm;
 __ro_after_init unsigned long poking_addr;
 
@@ -957,28 +1011,29 @@ struct bp_patching_desc {
 
 static struct bp_patching_desc *bp_desc;
 
-static inline struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
+static __always_inline
+struct bp_patching_desc *try_get_desc(struct bp_patching_desc **descp)
 {
-	struct bp_patching_desc *desc = READ_ONCE(*descp); /* rcu_dereference */
+	struct bp_patching_desc *desc = __READ_ONCE(*descp); /* rcu_dereference */
 
-	if (!desc || !atomic_inc_not_zero(&desc->refs))
+	if (!desc || !arch_atomic_inc_not_zero(&desc->refs))
 		return NULL;
 
 	return desc;
 }
 
-static inline void put_desc(struct bp_patching_desc *desc)
+static __always_inline void put_desc(struct bp_patching_desc *desc)
 {
 	smp_mb__before_atomic();
-	atomic_dec(&desc->refs);
+	arch_atomic_dec(&desc->refs);
 }
 
-static inline void *text_poke_addr(struct text_poke_loc *tp)
+static __always_inline void *text_poke_addr(struct text_poke_loc *tp)
 {
 	return _stext + tp->rel_addr;
 }
 
-static int notrace patch_cmp(const void *key, const void *elt)
+static __always_inline int patch_cmp(const void *key, const void *elt)
 {
 	struct text_poke_loc *tp = (struct text_poke_loc *) elt;
 
@@ -988,9 +1043,8 @@ static int notrace patch_cmp(const void *key, const void *elt)
 		return 1;
 	return 0;
 }
-NOKPROBE_SYMBOL(patch_cmp);
 
-int notrace poke_int3_handler(struct pt_regs *regs)
+int noinstr poke_int3_handler(struct pt_regs *regs)
 {
 	struct bp_patching_desc *desc;
 	struct text_poke_loc *tp;
@@ -1023,9 +1077,9 @@ int notrace poke_int3_handler(struct pt_regs *regs)
 	 * Skip the binary search if there is a single member in the vector.
 	 */
 	if (unlikely(desc->nr_entries > 1)) {
-		tp = bsearch(ip, desc->vec, desc->nr_entries,
-			     sizeof(struct text_poke_loc),
-			     patch_cmp);
+		tp = __inline_bsearch(ip, desc->vec, desc->nr_entries,
+				      sizeof(struct text_poke_loc),
+				      patch_cmp);
 		if (!tp)
 			goto out_put;
 	} else {
@@ -1064,7 +1118,6 @@ out_put:
 	put_desc(desc);
 	return ret;
 }
-NOKPROBE_SYMBOL(poke_int3_handler);
 
 #define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
 static struct text_poke_loc tp_vec[TP_VEC_MAX];