From: Josh Poimboeuf jpoimboe@redhat.com
[ Upstream commit 9f255b632bf12c4dd7fc31caee89aa991ef75176 ]
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.
Link: http://lkml.kernel.org/r/ab43d56ab909469ac5d2520c5d944ad6d4abd476.1560474114...
Reported-by: Johannes Erdfelt johannes@erdfelt.com Fixes: 444d13ff10fb ("modules: add ro_after_init support") Acked-by: Jessica Yu jeyu@kernel.org Reviewed-by: Petr Mladek pmladek@suse.com Reviewed-by: Miroslav Benes mbenes@suse.cz Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/livepatch/core.c | 6 ++++++ kernel/trace/ftrace.c | 10 +++++++++- 2 files changed, 15 insertions(+), 1 deletion(-)
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c index 5b77a7314e01..722c27c40e5b 100644 --- a/kernel/livepatch/core.c +++ b/kernel/livepatch/core.c @@ -30,6 +30,7 @@ #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" @@ -708,16 +709,21 @@ 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/trace/ftrace.c b/kernel/trace/ftrace.c index 90348b343460..50ba14591996 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -35,6 +35,7 @@ #include <linux/hash.h> #include <linux/rcupdate.h> #include <linux/kprobes.h> +#include <linux/memory.h>
#include <trace/events/sched.h>
@@ -2627,10 +2628,12 @@ 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. @@ -2642,6 +2645,9 @@ 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, @@ -5762,6 +5768,7 @@ 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; @@ -5823,6 +5830,7 @@ 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);