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Message-ID: <1509534034-104533-1-git-send-email-zhouchengming1@huawei.com>
Date: Wed, 1 Nov 2017 19:00:34 +0800
From: Zhou Chengming <zhouchengming1@...wei.com>
To: <mingo@...nel.org>, <mhiramat@...nel.org>, <rostedt@...dmis.org>,
<peterz@...radead.org>, <bp@...e.de>, <hpa@...or.com>,
<davem@...emloft.net>, <jkosina@...e.cz>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
<zhouchengming1@...wei.com>
Subject: [PATCH v3] kprobes, x86/alternatives: use text_mutex to protect smp_alt_modules
Changes:
- Add a comment about text_mutex protecting this on x86.
- Add a lockdep_assert_held() check.
Fixes: 2cfa197 "ftrace/alternatives: Introducing *_text_reserved
functions"
We use alternatives_text_reserved() to check if the address is in
the fixed pieces of alternative reserved, but the problem is that
we don't hold the smp_alt mutex when call this function. So the list
traversal may encounter a deleted list_head if another path is doing
alternatives_smp_module_del().
One solution is that we can hold smp_alt mutex before call this
function, but the difficult point is that the callers of this
functions, arch_prepare_kprobe() and arch_prepare_optimized_kprobe(),
are called inside the text_mutex. So we must hold smp_alt mutex
before we go into these arch dependent code. But we can't now,
the smp_alt mutex is the arch dependent part, only x86 has it.
Maybe we can export another arch dependent callback to solve this.
But there is a simpler way to handle this problem. We can reuse the
text_mutex to protect smp_alt_modules instead of using another mutex.
And all the arch dependent checks of kprobes are inside the text_mutex,
so it's safe now.
Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>
Signed-off-by: Zhou Chengming <zhouchengming1@...wei.com>
---
arch/x86/kernel/alternative.c | 26 +++++++++++++-------------
kernel/extable.c | 2 ++
2 files changed, 15 insertions(+), 13 deletions(-)
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 3344d33..3ad92fe 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -442,7 +442,6 @@ static void alternatives_smp_lock(const s32 *start, const s32 *end,
{
const s32 *poff;
- mutex_lock(&text_mutex);
for (poff = start; poff < end; poff++) {
u8 *ptr = (u8 *)poff + *poff;
@@ -452,7 +451,6 @@ static void alternatives_smp_lock(const s32 *start, const s32 *end,
if (*ptr == 0x3e)
text_poke(ptr, ((unsigned char []){0xf0}), 1);
}
- mutex_unlock(&text_mutex);
}
static void alternatives_smp_unlock(const s32 *start, const s32 *end,
@@ -460,7 +458,6 @@ static void alternatives_smp_unlock(const s32 *start, const s32 *end,
{
const s32 *poff;
- mutex_lock(&text_mutex);
for (poff = start; poff < end; poff++) {
u8 *ptr = (u8 *)poff + *poff;
@@ -470,7 +467,6 @@ static void alternatives_smp_unlock(const s32 *start, const s32 *end,
if (*ptr == 0xf0)
text_poke(ptr, ((unsigned char []){0x3E}), 1);
}
- mutex_unlock(&text_mutex);
}
struct smp_alt_module {
@@ -489,8 +485,7 @@ struct smp_alt_module {
struct list_head next;
};
static LIST_HEAD(smp_alt_modules);
-static DEFINE_MUTEX(smp_alt);
-static bool uniproc_patched = false; /* protected by smp_alt */
+static bool uniproc_patched = false; /* protected by text_mutex */
void __init_or_module alternatives_smp_module_add(struct module *mod,
char *name,
@@ -499,7 +494,7 @@ void __init_or_module alternatives_smp_module_add(struct module *mod,
{
struct smp_alt_module *smp;
- mutex_lock(&smp_alt);
+ mutex_lock(&text_mutex);
if (!uniproc_patched)
goto unlock;
@@ -526,14 +521,14 @@ void __init_or_module alternatives_smp_module_add(struct module *mod,
smp_unlock:
alternatives_smp_unlock(locks, locks_end, text, text_end);
unlock:
- mutex_unlock(&smp_alt);
+ mutex_unlock(&text_mutex);
}
void __init_or_module alternatives_smp_module_del(struct module *mod)
{
struct smp_alt_module *item;
- mutex_lock(&smp_alt);
+ mutex_lock(&text_mutex);
list_for_each_entry(item, &smp_alt_modules, next) {
if (mod != item->mod)
continue;
@@ -541,7 +536,7 @@ void __init_or_module alternatives_smp_module_del(struct module *mod)
kfree(item);
break;
}
- mutex_unlock(&smp_alt);
+ mutex_unlock(&text_mutex);
}
void alternatives_enable_smp(void)
@@ -551,7 +546,7 @@ void alternatives_enable_smp(void)
/* Why bother if there are no other CPUs? */
BUG_ON(num_possible_cpus() == 1);
- mutex_lock(&smp_alt);
+ mutex_lock(&text_mutex);
if (uniproc_patched) {
pr_info("switching to SMP code\n");
@@ -563,10 +558,13 @@ void alternatives_enable_smp(void)
mod->text, mod->text_end);
uniproc_patched = false;
}
- mutex_unlock(&smp_alt);
+ mutex_unlock(&text_mutex);
}
-/* Return 1 if the address range is reserved for smp-alternatives */
+/*
+ * Return 1 if the address range is reserved for smp-alternatives.
+ * Must hold text_mutex.
+ */
int alternatives_text_reserved(void *start, void *end)
{
struct smp_alt_module *mod;
@@ -574,6 +572,8 @@ int alternatives_text_reserved(void *start, void *end)
u8 *text_start = start;
u8 *text_end = end;
+ lockdep_assert_held(&text_mutex);
+
list_for_each_entry(mod, &smp_alt_modules, next) {
if (mod->text > text_end || mod->text_end < text_start)
continue;
diff --git a/kernel/extable.c b/kernel/extable.c
index 9aa1cc4..ec64cf5 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -31,6 +31,8 @@
* mutex protecting text section modification (dynamic code patching).
* some users need to sleep (allocating memory...) while they hold this lock.
*
+ * Note: also protect smp alternatives modification on x86.
+ *
* NOT exported to modules - patching kernel text is a really delicate matter.
*/
DEFINE_MUTEX(text_mutex);
--
1.8.3.1
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