kprobes/x86: Make insn buffer always ROX and use text_poke()

Make insn buffer always ROX and use text_poke() to write
the copied instructions instead of set_memory_*().
This makes instruction buffer stronger against other
kernel subsystems because there is no window time
to modify the buffer.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S . Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/150304463032.17009.14195368040691676813.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/kprobes/common.h

@@ -75,11 +75,11 @@ extern unsigned long recover_probed_instruction(kprobe_opcode_t *buf,
  * Copy an instruction and adjust the displacement if the instruction
  * uses the %rip-relative addressing mode.
  */
-extern int __copy_instruction(u8 *dest, u8 *src, struct insn *insn);
+extern int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn);
 
 /* Generate a relative-jump/call instruction */
-extern void synthesize_reljump(void *from, void *to);
-extern void synthesize_relcall(void *from, void *to);
+extern void synthesize_reljump(void *dest, void *from, void *to);
+extern void synthesize_relcall(void *dest, void *from, void *to);
 
 #ifdef	CONFIG_OPTPROBES
 extern int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter);

arch/x86/kernel/kprobes/core.c

@@ -119,29 +119,29 @@ struct kretprobe_blackpoint kretprobe_blacklist[] = {
 const int kretprobe_blacklist_size = ARRAY_SIZE(kretprobe_blacklist);
 
 static nokprobe_inline void
-__synthesize_relative_insn(void *from, void *to, u8 op)
+__synthesize_relative_insn(void *dest, void *from, void *to, u8 op)
 {
 	struct __arch_relative_insn {
 		u8 op;
 		s32 raddr;
 	} __packed *insn;
 
-	insn = (struct __arch_relative_insn *)from;
+	insn = (struct __arch_relative_insn *)dest;
 	insn->raddr = (s32)((long)(to) - ((long)(from) + 5));
 	insn->op = op;
 }
 
 /* Insert a jump instruction at address 'from', which jumps to address 'to'.*/
-void synthesize_reljump(void *from, void *to)
+void synthesize_reljump(void *dest, void *from, void *to)
 {
-	__synthesize_relative_insn(from, to, RELATIVEJUMP_OPCODE);
+	__synthesize_relative_insn(dest, from, to, RELATIVEJUMP_OPCODE);
 }
 NOKPROBE_SYMBOL(synthesize_reljump);
 
 /* Insert a call instruction at address 'from', which calls address 'to'.*/
-void synthesize_relcall(void *from, void *to)
+void synthesize_relcall(void *dest, void *from, void *to)
 {
-	__synthesize_relative_insn(from, to, RELATIVECALL_OPCODE);
+	__synthesize_relative_insn(dest, from, to, RELATIVECALL_OPCODE);
 }
 NOKPROBE_SYMBOL(synthesize_relcall);
 
@@ -346,10 +346,11 @@ static int is_IF_modifier(kprobe_opcode_t *insn)
 /*
  * Copy an instruction with recovering modified instruction by kprobes
  * and adjust the displacement if the instruction uses the %rip-relative
- * addressing mode.
+ * addressing mode. Note that since @real will be the final place of copied
+ * instruction, displacement must be adjust by @real, not @dest.
  * This returns the length of copied instruction, or 0 if it has an error.
  */
-int __copy_instruction(u8 *dest, u8 *src, struct insn *insn)
+int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn)
 {
 	kprobe_opcode_t buf[MAX_INSN_SIZE];
 	unsigned long recovered_insn =
@@ -387,11 +388,11 @@ int __copy_instruction(u8 *dest, u8 *src, struct insn *insn)
 		 * have given.
 		 */
 		newdisp = (u8 *) src + (s64) insn->displacement.value
-			  - (u8 *) dest;
+			  - (u8 *) real;
 		if ((s64) (s32) newdisp != newdisp) {
 			pr_err("Kprobes error: new displacement does not fit into s32 (%llx)\n", newdisp);
 			pr_err("\tSrc: %p, Dest: %p, old disp: %x\n",
-				src, dest, insn->displacement.value);
+				src, real, insn->displacement.value);
 			return 0;
 		}
 		disp = (u8 *) dest + insn_offset_displacement(insn);
@@ -402,20 +403,38 @@ int __copy_instruction(u8 *dest, u8 *src, struct insn *insn)
 }
 
 /* Prepare reljump right after instruction to boost */
-static void prepare_boost(struct kprobe *p, struct insn *insn)
+static int prepare_boost(kprobe_opcode_t *buf, struct kprobe *p,
+			  struct insn *insn)
 {
+	int len = insn->length;
+
 	if (can_boost(insn, p->addr) &&
-	    MAX_INSN_SIZE - insn->length >= RELATIVEJUMP_SIZE) {
+	    MAX_INSN_SIZE - len >= RELATIVEJUMP_SIZE) {
 		/*
 		 * These instructions can be executed directly if it
 		 * jumps back to correct address.
 		 */
-		synthesize_reljump(p->ainsn.insn + insn->length,
+		synthesize_reljump(buf + len, p->ainsn.insn + len,
 				   p->addr + insn->length);
+		len += RELATIVEJUMP_SIZE;
 		p->ainsn.boostable = true;
 	} else {
 		p->ainsn.boostable = false;
 	}
+
+	return len;
+}
+
+/* Make page to RO mode when allocate it */
+void *alloc_insn_page(void)
+{
+	void *page;
+
+	page = module_alloc(PAGE_SIZE);
+	if (page)
+		set_memory_ro((unsigned long)page & PAGE_MASK, 1);
+
+	return page;
 }
 
 /* Recover page to RW mode before releasing it */
@@ -429,28 +448,28 @@ void free_insn_page(void *page)
 static int arch_copy_kprobe(struct kprobe *p)
 {
 	struct insn insn;
+	kprobe_opcode_t buf[MAX_INSN_SIZE];
 	int len;
 
-	set_memory_rw((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
-
 	/* Copy an instruction with recovering if other optprobe modifies it.*/
-	len = __copy_instruction(p->ainsn.insn, p->addr, &insn);
+	len = __copy_instruction(buf, p->addr, p->ainsn.insn, &insn);
 	if (!len)
 		return -EINVAL;
 
 	/*
 	 * __copy_instruction can modify the displacement of the instruction,
 	 * but it doesn't affect boostable check.
 	 */
-	prepare_boost(p, &insn);
-
-	set_memory_ro((unsigned long)p->ainsn.insn & PAGE_MASK, 1);
+	len = prepare_boost(buf, p, &insn);
 
 	/* Check whether the instruction modifies Interrupt Flag or not */
-	p->ainsn.if_modifier = is_IF_modifier(p->ainsn.insn);
+	p->ainsn.if_modifier = is_IF_modifier(buf);
 
 	/* Also, displacement change doesn't affect the first byte */
-	p->opcode = p->ainsn.insn[0];
+	p->opcode = buf[0];
+
+	/* OK, write back the instruction(s) into ROX insn buffer */
+	text_poke(p->ainsn.insn, buf, len);
 
 	return 0;
 }

arch/x86/kernel/kprobes/opt.c

@@ -184,13 +184,13 @@ optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(optimized_callback);
 
-static int copy_optimized_instructions(u8 *dest, u8 *src)
+static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real)
 {
 	struct insn insn;
 	int len = 0, ret;
 
 	while (len < RELATIVEJUMP_SIZE) {
-		ret = __copy_instruction(dest + len, src + len, &insn);
+		ret = __copy_instruction(dest + len, src + len, real, &insn);
 		if (!ret || !can_boost(&insn, src + len))
 			return -EINVAL;
 		len += ret;
@@ -343,57 +343,66 @@ void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
 				  struct kprobe *__unused)
 {
-	u8 *buf;
-	int ret;
+	u8 *buf = NULL, *slot;
+	int ret, len;
 	long rel;
 
 	if (!can_optimize((unsigned long)op->kp.addr))
 		return -EILSEQ;
 
-	op->optinsn.insn = get_optinsn_slot();
-	if (!op->optinsn.insn)
+	buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL);
+	if (!buf)
 		return -ENOMEM;
 
+	op->optinsn.insn = slot = get_optinsn_slot();
+	if (!slot) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
 	/*
 	 * Verify if the address gap is in 2GB range, because this uses
 	 * a relative jump.
 	 */
-	rel = (long)op->optinsn.insn - (long)op->kp.addr + RELATIVEJUMP_SIZE;
+	rel = (long)slot - (long)op->kp.addr + RELATIVEJUMP_SIZE;
 	if (abs(rel) > 0x7fffffff) {
-		__arch_remove_optimized_kprobe(op, 0);
-		return -ERANGE;
+		ret = -ERANGE;
+		goto err;
 	}
 
-	buf = (u8 *)op->optinsn.insn;
-	set_memory_rw((unsigned long)buf & PAGE_MASK, 1);
+	/* Copy arch-dep-instance from template */
+	memcpy(buf, &optprobe_template_entry, TMPL_END_IDX);
 
 	/* Copy instructions into the out-of-line buffer */
-	ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr);
-	if (ret < 0) {
-		__arch_remove_optimized_kprobe(op, 0);
-		return ret;
-	}
+	ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr,
+					  slot + TMPL_END_IDX);
+	if (ret < 0)
+		goto err;
 	op->optinsn.size = ret;
-
-	/* Copy arch-dep-instance from template */
-	memcpy(buf, &optprobe_template_entry, TMPL_END_IDX);
+	len = TMPL_END_IDX + op->optinsn.size;
 
 	/* Set probe information */
 	synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);
 
 	/* Set probe function call */
-	synthesize_relcall(buf + TMPL_CALL_IDX, optimized_callback);
+	synthesize_relcall(buf + TMPL_CALL_IDX,
+			   slot + TMPL_CALL_IDX, optimized_callback);
 
 	/* Set returning jmp instruction at the tail of out-of-line buffer */
-	synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
+	synthesize_reljump(buf + len, slot + len,
 			   (u8 *)op->kp.addr + op->optinsn.size);
-
-	set_memory_ro((unsigned long)buf & PAGE_MASK, 1);
-
-	flush_icache_range((unsigned long) buf,
-			   (unsigned long) buf + TMPL_END_IDX +
-			   op->optinsn.size + RELATIVEJUMP_SIZE);
-	return 0;
+	len += RELATIVEJUMP_SIZE;
+
+	/* We have to use text_poke for instuction buffer because it is RO */
+	text_poke(slot, buf, len);
+	ret = 0;
+out:
+	kfree(buf);
+	return ret;
+
+err:
+	__arch_remove_optimized_kprobe(op, 0);
+	goto out;
 }
 
 /*

kernel/kprobes.c

@@ -117,7 +117,7 @@ enum kprobe_slot_state {
 	SLOT_USED = 2,
 };
 
-static void *alloc_insn_page(void)
+void __weak *alloc_insn_page(void)
 {
 	return module_alloc(PAGE_SIZE);
 }