From: Masami Hiramatsu (Google) <mhiramat@kernel•org>
To: Stephen Brennan <stephen.s.brennan@oracle•com>
Cc: Mark Rutland <mark.rutland@arm•com>,
x86@kernel•org, Dave Hansen <dave.hansen@linux•intel.com>,
"James E.J. Bottomley" <James.Bottomley@HansenPartnership•com>,
Guo Ren <guoren@kernel•org>,
linux-csky@vger•kernel.org, "H. Peter Anvin" <hpa@zytor•com>,
Alexander Gordeev <agordeev@linux•ibm.com>,
WANG Xuerui <kernel@xen0n•name>,
linux-s390@vger•kernel.org, Helge Deller <deller@gmx•de>,
Huacai Chen <chenhuacai@kernel•org>,
"Aneesh Kumar K.V" <aneesh.kumar@kernel•org>,
Ingo Molnar <mingo@redhat•com>,
"Naveen N. Rao" <naveen.n.rao@linux•ibm.com>,
Christian Borntraeger <borntraeger@linux•ibm.com>,
linux-trace-kernel@vger•kernel.org,
Albert Ou <aou@eecs•berkeley.edu>,
Vasily Gorbik <gor@linux•ibm.com>,
Heiko Carstens <hca@linux•ibm.com>,
Steven Rostedt <rostedt@goodmis•org>,
Borislav Petkov <bp@alien8•de>,
Nicholas Piggin <npiggin@gmail•com>,
loongarch@lists•linux.dev,
Paul Walmsley <paul.walmsley@sifive•com>,
Thomas Gleixner <tglx@linutronix•de>,
linux-parisc@vger•kernel.org, linux-kern el@vger•kernel.org,
linux-riscv@lists•infradead.org,
Palmer Dabbelt <palmer@dabbelt•com>,
Sven Schnelle <svens@linux•ibm.com>,
linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH] kprobe/ftrace: bail out if ftrace was killed
Date: Mon, 29 Apr 2024 22:48:03 +0900 [thread overview]
Message-ID: <20240429224803.49d420b514e22d51412e1602@kernel.org> (raw)
In-Reply-To: <20240426225834.993353-1-stephen.s.brennan@oracle.com>
Hi Stephen,
On Fri, 26 Apr 2024 15:58:34 -0700
Stephen Brennan <stephen.s.brennan@oracle•com> wrote:
> 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.
Hmm, indeed.
>
> 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.
OK, the patch looks good to me.
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel•org>
Thanks!
>
> Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle•com>
> ---
>
> Apologies for the wide net cast here. I recognize that a change like this
> may need to be split up and go through arch-specific trees. I hoped to get
> feedback on the patch itself. If it's satisfactory and the architecture
> maintainers prefer it split out, I'm glad to do it. Thanks!
>
> 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/ftrace.h | 2 ++
> 8 files changed, 23 insertions(+)
>
> diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c
> index 834cffcfbce3..3931bf9f707b 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(ftrace_is_dead()))
> + 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 73858c9029cc..82c952cb5be0 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(ftrace_is_dead()))
> + 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 621a4b386ae4..3660834f54c3 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(ftrace_is_dead()))
> + 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 072ebe7f290b..85eb55aa1457 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(ftrace_is_dead()))
> + 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 7142ec42e889..8814fbe4c888 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(ftrace_is_dead()))
> + 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 c46381ea04ec..ccbe8ccf945b 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(ftrace_is_dead()))
> + 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 dd2ec14adb77..c73f9ab7ff50 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(ftrace_is_dead()))
> + return;
> +
> bit = ftrace_test_recursion_trylock(ip, parent_ip);
> if (bit < 0)
> return;
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 54d53f345d14..ba83e99c1fbe 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -399,6 +399,7 @@ int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *a
> #define register_ftrace_function(ops) ({ 0; })
> #define unregister_ftrace_function(ops) ({ 0; })
> static inline void ftrace_kill(void) { }
> +static inline int ftrace_is_dead(void) { return 0; }
> static inline void ftrace_free_init_mem(void) { }
> static inline void ftrace_free_mem(struct module *mod, void *start, void *end) { }
> static inline int ftrace_lookup_symbols(const char **sorted_syms, size_t cnt, unsigned long *addrs)
> @@ -914,6 +915,7 @@ static inline bool is_ftrace_trampoline(unsigned long addr)
>
> /* totally disable ftrace - can not re-enable after this */
> void ftrace_kill(void);
> +int ftrace_is_dead(void);
>
> static inline void tracer_disable(void)
> {
> --
> 2.39.3
>
--
Masami Hiramatsu (Google) <mhiramat@kernel•org>
next prev parent reply other threads:[~2024-04-29 13:49 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-26 22:58 [PATCH] kprobe/ftrace: bail out if ftrace was killed Stephen Brennan
2024-04-29 13:48 ` Masami Hiramatsu [this message]
2024-04-29 17:47 ` Stephen Brennan
2024-04-29 17:47 ` [PATCH v2] " Stephen Brennan
2024-04-30 1:29 ` Steven Rostedt
2024-04-30 23:01 ` Stephen Brennan
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