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From:   Josh Poimboeuf <jpoimboe@redhat.com>
To:     Steven Rostedt <rostedt@goodmis.org>,
        Jiri Kosina <jikos@kernel.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Petr Mladek <pmladek@suse.com>, Jessica Yu <jeyu@kernel.org>
Cc:     Joe Lawrence <joe.lawrence@redhat.com>,
        linux-kernel@vger.kernel.org, live-patching@vger.kernel.org,
        Johannes Erdfelt <johannes@erdfelt.com>,
        Ingo Molnar <mingo@kernel.org>
Subject: [PATCH] livepatch: Fix ftrace module text permissions race
Date:   Wed, 29 May 2019 14:02:24 -0500
Message-Id: <bb69d4ac34111bbd9cb16180a6fafe471a88d80b.1559156299.git.jpoimboe@redhat.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

It's possible for livepatch and ftrace to be toggling a module's text
permissions at the same time, resulting in the following panic:

  BUG: unable to handle page fault for address: ffffffffc005b1d9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0003) - permissions violation
  PGD 3ea0c067 P4D 3ea0c067 PUD 3ea0e067 PMD 3cc13067 PTE 3b8a1061
  Oops: 0003 [#1] PREEMPT SMP PTI
  CPU: 1 PID: 453 Comm: insmod Tainted: G           O  K   5.2.0-rc1-a188339ca5 #1
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014
  RIP: 0010:apply_relocate_add+0xbe/0x14c
  Code: fa 0b 74 21 48 83 fa 18 74 38 48 83 fa 0a 75 40 eb 08 48 83 38 00 74 33 eb 53 83 38 00 75 4e 89 08 89 c8 eb 0a 83 38 00 75 43 <89> 08 48 63 c1 48 39 c8 74 2e eb 48 83 38 00 75 32 48 29 c1 89 08
  RSP: 0018:ffffb223c00dbb10 EFLAGS: 00010246
  RAX: ffffffffc005b1d9 RBX: 0000000000000000 RCX: ffffffff8b200060
  RDX: 000000000000000b RSI: 0000004b0000000b RDI: ffff96bdfcd33000
  RBP: ffffb223c00dbb38 R08: ffffffffc005d040 R09: ffffffffc005c1f0
  R10: ffff96bdfcd33c40 R11: ffff96bdfcd33b80 R12: 0000000000000018
  R13: ffffffffc005c1f0 R14: ffffffffc005e708 R15: ffffffff8b2fbc74
  FS:  00007f5f447beba8(0000) GS:ffff96bdff900000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: ffffffffc005b1d9 CR3: 000000003cedc002 CR4: 0000000000360ea0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   klp_init_object_loaded+0x10f/0x219
   ? preempt_latency_start+0x21/0x57
   klp_enable_patch+0x662/0x809
   ? virt_to_head_page+0x3a/0x3c
   ? kfree+0x8c/0x126
   patch_init+0x2ed/0x1000 [livepatch_test02]
   ? 0xffffffffc0060000
   do_one_initcall+0x9f/0x1c5
   ? kmem_cache_alloc_trace+0xc4/0xd4
   ? do_init_module+0x27/0x210
   do_init_module+0x5f/0x210
   load_module+0x1c41/0x2290
   ? fsnotify_path+0x3b/0x42
   ? strstarts+0x2b/0x2b
   ? kernel_read+0x58/0x65
   __do_sys_finit_module+0x9f/0xc3
   ? __do_sys_finit_module+0x9f/0xc3
   __x64_sys_finit_module+0x1a/0x1c
   do_syscall_64+0x52/0x61
   entry_SYSCALL_64_after_hwframe+0x44/0xa9

The above panic occurs when loading two modules at the same time with
ftrace enabled, where at least one of the modules is a livepatch module:

CPU0					CPU1
klp_enable_patch()
  klp_init_object_loaded()
    module_disable_ro()
    					ftrace_module_enable()
					  ftrace_arch_code_modify_post_process()
				    	    set_all_modules_text_ro()
      klp_write_object_relocations()
        apply_relocate_add()
	  *patches read-only code* - BOOM

A similar race exists when toggling ftrace while loading a livepatch
module.

Fix it by ensuring that the livepatch and ftrace code patching
operations -- and their respective permissions changes -- are protected
by the text_mutex.

Reported-by: Johannes Erdfelt <johannes@erdfelt.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 kernel/livepatch/core.c |  6 ++++++
 kernel/module.c         | 21 ++++++++++++++++++---
 kernel/trace/ftrace.c   | 10 +++++++++-
 3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index 2398832947c6..c4ce08f43bd6 100644
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -18,6 +18,7 @@
 #include <linux/elf.h>
 #include <linux/moduleloader.h>
 #include <linux/completion.h>
+#include <linux/memory.h>
 #include <asm/cacheflush.h>
 #include "core.h"
 #include "patch.h"
@@ -718,16 +719,21 @@ static int klp_init_object_loaded(struct klp_patch *patch,
 	struct klp_func *func;
 	int ret;
 
+	mutex_lock(&text_mutex);
+
 	module_disable_ro(patch->mod);
 	ret = klp_write_object_relocations(patch->mod, obj);
 	if (ret) {
 		module_enable_ro(patch->mod, true);
+		mutex_unlock(&text_mutex);
 		return ret;
 	}
 
 	arch_klp_init_object_loaded(patch, obj);
 	module_enable_ro(patch->mod, true);
 
+	mutex_unlock(&text_mutex);
+
 	klp_for_each_func(obj, func) {
 		ret = klp_find_object_symbol(obj->name, func->old_name,
 					     func->old_sympos,
diff --git a/kernel/module.c b/kernel/module.c
index 6e6712b3aaf5..3c056b56aefa 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -64,6 +64,7 @@
 #include <linux/bsearch.h>
 #include <linux/dynamic_debug.h>
 #include <linux/audit.h>
+#include <linux/memory.h>
 #include <uapi/linux/module.h>
 #include "module-internal.h"
 
@@ -1943,6 +1944,8 @@ static void frob_writable_data(const struct module_layout *layout,
 /* livepatching wants to disable read-only so it can frob module. */
 void module_disable_ro(const struct module *mod)
 {
+	lockdep_assert_held(&text_mutex);
+
 	if (!rodata_enabled)
 		return;
 
@@ -1953,7 +1956,7 @@ void module_disable_ro(const struct module *mod)
 	frob_rodata(&mod->init_layout, set_memory_rw);
 }
 
-void module_enable_ro(const struct module *mod, bool after_init)
+static void __module_enable_ro(const struct module *mod, bool after_init)
 {
 	if (!rodata_enabled)
 		return;
@@ -1974,6 +1977,13 @@ void module_enable_ro(const struct module *mod, bool after_init)
 		frob_ro_after_init(&mod->core_layout, set_memory_ro);
 }
 
+void module_enable_ro(const struct module *mod, bool after_init)
+{
+	lockdep_assert_held(&text_mutex);
+
+	__module_enable_ro(mod, after_init);
+}
+
 static void module_enable_nx(const struct module *mod)
 {
 	frob_rodata(&mod->core_layout, set_memory_nx);
@@ -1988,6 +1998,8 @@ void set_all_modules_text_rw(void)
 {
 	struct module *mod;
 
+	lockdep_assert_held(&text_mutex);
+
 	if (!rodata_enabled)
 		return;
 
@@ -2007,6 +2019,8 @@ void set_all_modules_text_ro(void)
 {
 	struct module *mod;
 
+	lockdep_assert_held(&text_mutex);
+
 	if (!rodata_enabled)
 		return;
 
@@ -2027,6 +2041,7 @@ void set_all_modules_text_ro(void)
 	mutex_unlock(&module_mutex);
 }
 #else
+static void __module_enable_ro(const struct module *mod, bool after_init) { }
 static void module_enable_nx(const struct module *mod) { }
 #endif
 
@@ -3519,7 +3534,7 @@ static noinline int do_init_module(struct module *mod)
 	/* Switch to core kallsyms now init is done: kallsyms may be walking! */
 	rcu_assign_pointer(mod->kallsyms, &mod->core_kallsyms);
 #endif
-	module_enable_ro(mod, true);
+	__module_enable_ro(mod, true);
 	mod_tree_remove_init(mod);
 	module_arch_freeing_init(mod);
 	mod->init_layout.base = NULL;
@@ -3626,7 +3641,7 @@ static int complete_formation(struct module *mod, struct load_info *info)
 	/* This relies on module_mutex for list integrity. */
 	module_bug_finalize(info->hdr, info->sechdrs, mod);
 
-	module_enable_ro(mod, false);
+	__module_enable_ro(mod, false);
 	module_enable_nx(mod);
 
 	/* Mark state as coming so strong_try_module_get() ignores us,
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a12aff849c04..8259d4ba8b00 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -34,6 +34,7 @@
 #include <linux/hash.h>
 #include <linux/rcupdate.h>
 #include <linux/kprobes.h>
+#include <linux/memory.h>
 
 #include <trace/events/sched.h>
 
@@ -2610,10 +2611,12 @@ static void ftrace_run_update_code(int command)
 {
 	int ret;
 
+	mutex_lock(&text_mutex);
+
 	ret = ftrace_arch_code_modify_prepare();
 	FTRACE_WARN_ON(ret);
 	if (ret)
-		return;
+		goto out_unlock;
 
 	/*
 	 * By default we use stop_machine() to modify the code.
@@ -2625,6 +2628,9 @@ static void ftrace_run_update_code(int command)
 
 	ret = ftrace_arch_code_modify_post_process();
 	FTRACE_WARN_ON(ret);
+
+out_unlock:
+	mutex_unlock(&text_mutex);
 }
 
 static void ftrace_run_modify_code(struct ftrace_ops *ops, int command,
@@ -5776,6 +5782,7 @@ void ftrace_module_enable(struct module *mod)
 	struct ftrace_page *pg;
 
 	mutex_lock(&ftrace_lock);
+	mutex_lock(&text_mutex);
 
 	if (ftrace_disabled)
 		goto out_unlock;
@@ -5837,6 +5844,7 @@ void ftrace_module_enable(struct module *mod)
 		ftrace_arch_code_modify_post_process();
 
  out_unlock:
+	mutex_unlock(&text_mutex);
 	mutex_unlock(&ftrace_lock);
 
 	process_cached_mods(mod->name);
-- 
2.20.1