[PATCH AUTOSEL 6.6 4/4] kprobe/ftrace: bail out if ftrace was killed
Sasha Levin
sashal at kernel.org
Mon May 27 19:18:53 PDT 2024
From: Stephen Brennan <stephen.s.brennan at oracle.com>
[ Upstream commit 1a7d0890dd4a502a202aaec792a6c04e6e049547 ]
If an error happens in ftrace, ftrace_kill() will prevent disarming
kprobes. Eventually, the ftrace_ops associated with the kprobes will be
freed, yet the kprobes will still be active, and when triggered, they
will use the freed memory, likely resulting in a page fault and panic.
This behavior can be reproduced quite easily, by creating a kprobe and
then triggering a ftrace_kill(). For simplicity, we can simulate an
ftrace error with a kernel module like [1]:
[1]: https://github.com/brenns10/kernel_stuff/tree/master/ftrace_killer
sudo perf probe --add commit_creds
sudo perf trace -e probe:commit_creds
# In another terminal
make
sudo insmod ftrace_killer.ko # calls ftrace_kill(), simulating bug
# Back to perf terminal
# ctrl-c
sudo perf probe --del commit_creds
After a short period, a page fault and panic would occur as the kprobe
continues to execute and uses the freed ftrace_ops. While ftrace_kill()
is supposed to be used only in extreme circumstances, it is invoked in
FTRACE_WARN_ON() and so there are many places where an unexpected bug
could be triggered, yet the system may continue operating, possibly
without the administrator noticing. If ftrace_kill() does not panic the
system, then we should do everything we can to continue operating,
rather than leave a ticking time bomb.
Link: https://lore.kernel.org/all/20240501162956.229427-1-stephen.s.brennan@oracle.com/
Signed-off-by: Stephen Brennan <stephen.s.brennan at oracle.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat at kernel.org>
Acked-by: Guo Ren <guoren at kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt at goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat at kernel.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
arch/csky/kernel/probes/ftrace.c | 3 +++
arch/loongarch/kernel/ftrace_dyn.c | 3 +++
arch/parisc/kernel/ftrace.c | 3 +++
arch/powerpc/kernel/kprobes-ftrace.c | 3 +++
arch/riscv/kernel/probes/ftrace.c | 3 +++
arch/s390/kernel/ftrace.c | 3 +++
arch/x86/kernel/kprobes/ftrace.c | 3 +++
include/linux/kprobes.h | 7 +++++++
kernel/kprobes.c | 6 ++++++
kernel/trace/ftrace.c | 1 +
10 files changed, 35 insertions(+)
diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c
index 834cffcfbce32..7ba4b98076de1 100644
--- a/arch/csky/kernel/probes/ftrace.c
+++ b/arch/csky/kernel/probes/ftrace.c
@@ -12,6 +12,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe_ctlblk *kcb;
struct pt_regs *regs;
+ if (unlikely(kprobe_ftrace_disabled))
+ return;
+
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;
diff --git a/arch/loongarch/kernel/ftrace_dyn.c b/arch/loongarch/kernel/ftrace_dyn.c
index 73858c9029cc9..bff058317062e 100644
--- a/arch/loongarch/kernel/ftrace_dyn.c
+++ b/arch/loongarch/kernel/ftrace_dyn.c
@@ -287,6 +287,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe *p;
struct kprobe_ctlblk *kcb;
+ if (unlikely(kprobe_ftrace_disabled))
+ return;
+
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;
diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c
index 621a4b386ae4f..c91f9c2e61ed2 100644
--- a/arch/parisc/kernel/ftrace.c
+++ b/arch/parisc/kernel/ftrace.c
@@ -206,6 +206,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe *p;
int bit;
+ if (unlikely(kprobe_ftrace_disabled))
+ return;
+
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;
diff --git a/arch/powerpc/kernel/kprobes-ftrace.c b/arch/powerpc/kernel/kprobes-ftrace.c
index 072ebe7f290ba..f8208c027148f 100644
--- a/arch/powerpc/kernel/kprobes-ftrace.c
+++ b/arch/powerpc/kernel/kprobes-ftrace.c
@@ -21,6 +21,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long parent_nip,
struct pt_regs *regs;
int bit;
+ if (unlikely(kprobe_ftrace_disabled))
+ return;
+
bit = ftrace_test_recursion_trylock(nip, parent_nip);
if (bit < 0)
return;
diff --git a/arch/riscv/kernel/probes/ftrace.c b/arch/riscv/kernel/probes/ftrace.c
index 7142ec42e889f..a69dfa610aa85 100644
--- a/arch/riscv/kernel/probes/ftrace.c
+++ b/arch/riscv/kernel/probes/ftrace.c
@@ -11,6 +11,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe_ctlblk *kcb;
int bit;
+ if (unlikely(kprobe_ftrace_disabled))
+ return;
+
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index c46381ea04ecb..7f6f8c438c265 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -296,6 +296,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe *p;
int bit;
+ if (unlikely(kprobe_ftrace_disabled))
+ return;
+
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;
diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index dd2ec14adb77b..15af7e98e161a 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -21,6 +21,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct kprobe_ctlblk *kcb;
int bit;
+ if (unlikely(kprobe_ftrace_disabled))
+ return;
+
bit = ftrace_test_recursion_trylock(ip, parent_ip);
if (bit < 0)
return;
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 8de5d51a0b5e7..45d5b0a76b0bd 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -383,11 +383,15 @@ static inline void wait_for_kprobe_optimizer(void) { }
extern void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *ops, struct ftrace_regs *fregs);
extern int arch_prepare_kprobe_ftrace(struct kprobe *p);
+/* Set when ftrace has been killed: kprobes on ftrace must be disabled for safety */
+extern bool kprobe_ftrace_disabled __read_mostly;
+extern void kprobe_ftrace_kill(void);
#else
static inline int arch_prepare_kprobe_ftrace(struct kprobe *p)
{
return -EINVAL;
}
+static inline void kprobe_ftrace_kill(void) {}
#endif /* CONFIG_KPROBES_ON_FTRACE */
/* Get the kprobe at this addr (if any) - called with preemption disabled */
@@ -496,6 +500,9 @@ static inline void kprobe_flush_task(struct task_struct *tk)
static inline void kprobe_free_init_mem(void)
{
}
+static inline void kprobe_ftrace_kill(void)
+{
+}
static inline int disable_kprobe(struct kprobe *kp)
{
return -EOPNOTSUPP;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index c2841e5957130..c8720bed8ed6a 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1068,6 +1068,7 @@ static struct ftrace_ops kprobe_ipmodify_ops __read_mostly = {
static int kprobe_ipmodify_enabled;
static int kprobe_ftrace_enabled;
+bool kprobe_ftrace_disabled;
static int __arm_kprobe_ftrace(struct kprobe *p, struct ftrace_ops *ops,
int *cnt)
@@ -1136,6 +1137,11 @@ static int disarm_kprobe_ftrace(struct kprobe *p)
ipmodify ? &kprobe_ipmodify_ops : &kprobe_ftrace_ops,
ipmodify ? &kprobe_ipmodify_enabled : &kprobe_ftrace_enabled);
}
+
+void kprobe_ftrace_kill()
+{
+ kprobe_ftrace_disabled = true;
+}
#else /* !CONFIG_KPROBES_ON_FTRACE */
static inline int arm_kprobe_ftrace(struct kprobe *p)
{
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 83ba342aef31f..4bdaed40e30d0 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -7892,6 +7892,7 @@ void ftrace_kill(void)
ftrace_disabled = 1;
ftrace_enabled = 0;
ftrace_trace_function = ftrace_stub;
+ kprobe_ftrace_kill();
}
/**
--
2.43.0
More information about the linux-riscv
mailing list