Re: [PATCH 05/11 v2] kprobes/ftrace: Add recursion protection to the ftrace callback
On Fri, 30 Oct 2020 17:31:47 -0400
Steven Rostedt wrote:
> From: "Steven Rostedt (VMware)"
>
> If a ftrace callback does not supply its own recursion protection and
> does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will
> make a helper trampoline to do so before calling the callback instead of
> just calling the callback directly.
>
> The default for ftrace_ops is going to change. It will expect that handlers
> provide their own recursion protection, unless its ftrace_ops states
> otherwise.
>
> Link: https://lkml.kernel.org/r/20201028115613.140212...@goodmis.org
>
> Cc: Andrew Morton
> Cc: Masami Hiramatsu
> Cc: Guo Ren
> Cc: "James E.J. Bottomley"
> Cc: Helge Deller
> Cc: Michael Ellerman
> Cc: Benjamin Herrenschmidt
> Cc: Paul Mackerras
> Cc: Heiko Carstens
> Cc: Vasily Gorbik
> Cc: Christian Borntraeger
> Cc: Thomas Gleixner
> Cc: Borislav Petkov
> Cc: x...@kernel.org
> Cc: "H. Peter Anvin"
> Cc: "Naveen N. Rao"
> Cc: Anil S Keshavamurthy
> Cc: "David S. Miller"
> Cc: linux-c...@vger.kernel.org
> Cc: linux-par...@vger.kernel.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-s...@vger.kernel.org
> Signed-off-by: Steven Rostedt (VMware)
> ---
> arch/csky/kernel/probes/ftrace.c | 12 ++--
> arch/parisc/kernel/ftrace.c | 13 +++--
> arch/powerpc/kernel/kprobes-ftrace.c | 11 ++-
> arch/s390/kernel/ftrace.c| 13 +++--
> arch/x86/kernel/kprobes/ftrace.c | 12 ++--
> 5 files changed, 52 insertions(+), 9 deletions(-)
>
> diff --git a/arch/csky/kernel/probes/ftrace.c
> b/arch/csky/kernel/probes/ftrace.c
> index 5264763d05be..5eb2604fdf71 100644
> --- a/arch/csky/kernel/probes/ftrace.c
> +++ b/arch/csky/kernel/probes/ftrace.c
> @@ -13,16 +13,21 @@ int arch_check_ftrace_location(struct kprobe *p)
> void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
> struct ftrace_ops *ops, struct pt_regs *regs)
> {
> + int bit;
> bool lr_saver = false;
> struct kprobe *p;
> struct kprobe_ctlblk *kcb;
>
> - /* Preempt is disabled by ftrace */
> + bit = ftrace_test_recursion_trylock();
> + if (bit < 0)
> + return;
> +
> + preempt_disable_notrace();
> p = get_kprobe((kprobe_opcode_t *)ip);
> if (!p) {
> p = get_kprobe((kprobe_opcode_t *)(ip - MCOUNT_INSN_SIZE));
> if (unlikely(!p) || kprobe_disabled(p))
> - return;
> + goto out;
> lr_saver = true;
> }
>
> @@ -56,6 +61,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long
> parent_ip,
>*/
> __this_cpu_write(current_kprobe, NULL);
> }
> +out:
> + preempt_enable_notrace();
> + ftrace_test_recursion_unlock(bit);
> }
> NOKPROBE_SYMBOL(kprobe_ftrace_handler);
>
> diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c
> index 63e3ecb9da81..4b1fdf15662c 100644
> --- a/arch/parisc/kernel/ftrace.c
> +++ b/arch/parisc/kernel/ftrace.c
> @@ -208,13 +208,19 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned
> long parent_ip,
> {
> struct kprobe_ctlblk *kcb;
> struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip);
> + int bit;
>
> - if (unlikely(!p) || kprobe_disabled(p))
> + bit = ftrace_test_recursion_trylock();
> + if (bit < 0)
> return;
>
> + preempt_disable_notrace();
If we disable preempt here, we also move the get_kprobe() here as below.
(get_kprobe() accesses percpu variable)
p = get_kprobe((kprobe_opcode_t *)ip);
> + if (unlikely(!p) || kprobe_disabled(p))
> + goto out;
> +
> if (kprobe_running()) {
> kprobes_inc_nmissed_count(p);
> - return;
> + goto out;
> }
>
> __this_cpu_write(current_kprobe, p);
> @@ -235,6 +241,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned
> long parent_ip,
> }
> }
> __this_cpu_write(current_kprobe, NULL);
> +out:
> + preempt_enable_notrace();
> + ftrace_test_recursion_unlock(bit);
> }
> NOKPROBE_SYMBOL(kprobe_ftrace_handler);
>
> diff --git a/arch/powerpc/kernel/kprobes-ftrace.c
> b/arch/powerpc/kernel/kprobes-ftrace.c
> index 972cb28174b2..5df8d50c65ae 100644
> --- a/arch/powerpc/kernel/kprobes-ftrace.c
> +++ b/arch/powerpc/kernel/kprobes-ftrace.c
> @@ -18,10 +18,16 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned
> long parent_nip,
> {
> struct kprobe *p;
> struct kprobe_ctlblk *kcb;
> + int bit;
>
> + bit = ftrace_test_recursion_trylock();
> + if (bit < 0)
> + return;
> +
> + preempt_disable_notrace();
> p = get_kprobe((kprobe_opcode_t *)nip);
> if (unlikely(!p) || kprobe_disabled(p))
> - return;
> + goto out;
>
> kcb = get_kprobe_ctlblk();
> if (kprobe_running()) {
> @@ -52,6
[PATCH 05/11 v2] kprobes/ftrace: Add recursion protection to the ftrace callback
From: "Steven Rostedt (VMware)"
If a ftrace callback does not supply its own recursion protection and
does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will
make a helper trampoline to do so before calling the callback instead of
just calling the callback directly.
The default for ftrace_ops is going to change. It will expect that handlers
provide their own recursion protection, unless its ftrace_ops states
otherwise.
Link: https://lkml.kernel.org/r/20201028115613.140212...@goodmis.org
Cc: Andrew Morton
Cc: Masami Hiramatsu
Cc: Guo Ren
Cc: "James E.J. Bottomley"
Cc: Helge Deller
Cc: Michael Ellerman
Cc: Benjamin Herrenschmidt
Cc: Paul Mackerras
Cc: Heiko Carstens
Cc: Vasily Gorbik
Cc: Christian Borntraeger
Cc: Thomas Gleixner
Cc: Borislav Petkov
Cc: x...@kernel.org
Cc: "H. Peter Anvin"
Cc: "Naveen N. Rao"
Cc: Anil S Keshavamurthy
Cc: "David S. Miller"
Cc: linux-c...@vger.kernel.org
Cc: linux-par...@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s...@vger.kernel.org
Signed-off-by: Steven Rostedt (VMware)
---
arch/csky/kernel/probes/ftrace.c | 12 ++--
arch/parisc/kernel/ftrace.c | 13 +++--
arch/powerpc/kernel/kprobes-ftrace.c | 11 ++-
arch/s390/kernel/ftrace.c| 13 +++--
arch/x86/kernel/kprobes/ftrace.c | 12 ++--
5 files changed, 52 insertions(+), 9 deletions(-)
diff --git a/arch/csky/kernel/probes/ftrace.c b/arch/csky/kernel/probes/ftrace.c
index 5264763d05be..5eb2604fdf71 100644
--- a/arch/csky/kernel/probes/ftrace.c
+++ b/arch/csky/kernel/probes/ftrace.c
@@ -13,16 +13,21 @@ int arch_check_ftrace_location(struct kprobe *p)
void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
struct ftrace_ops *ops, struct pt_regs *regs)
{
+ int bit;
bool lr_saver = false;
struct kprobe *p;
struct kprobe_ctlblk *kcb;
- /* Preempt is disabled by ftrace */
+ bit = ftrace_test_recursion_trylock();
+ if (bit < 0)
+ return;
+
+ preempt_disable_notrace();
p = get_kprobe((kprobe_opcode_t *)ip);
if (!p) {
p = get_kprobe((kprobe_opcode_t *)(ip - MCOUNT_INSN_SIZE));
if (unlikely(!p) || kprobe_disabled(p))
- return;
+ goto out;
lr_saver = true;
}
@@ -56,6 +61,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long
parent_ip,
*/
__this_cpu_write(current_kprobe, NULL);
}
+out:
+ preempt_enable_notrace();
+ ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/arch/parisc/kernel/ftrace.c b/arch/parisc/kernel/ftrace.c
index 63e3ecb9da81..4b1fdf15662c 100644
--- a/arch/parisc/kernel/ftrace.c
+++ b/arch/parisc/kernel/ftrace.c
@@ -208,13 +208,19 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned
long parent_ip,
{
struct kprobe_ctlblk *kcb;
struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip);
+ int bit;
- if (unlikely(!p) || kprobe_disabled(p))
+ bit = ftrace_test_recursion_trylock();
+ if (bit < 0)
return;
+ preempt_disable_notrace();
+ if (unlikely(!p) || kprobe_disabled(p))
+ goto out;
+
if (kprobe_running()) {
kprobes_inc_nmissed_count(p);
- return;
+ goto out;
}
__this_cpu_write(current_kprobe, p);
@@ -235,6 +241,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long
parent_ip,
}
}
__this_cpu_write(current_kprobe, NULL);
+out:
+ preempt_enable_notrace();
+ ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/arch/powerpc/kernel/kprobes-ftrace.c
b/arch/powerpc/kernel/kprobes-ftrace.c
index 972cb28174b2..5df8d50c65ae 100644
--- a/arch/powerpc/kernel/kprobes-ftrace.c
+++ b/arch/powerpc/kernel/kprobes-ftrace.c
@@ -18,10 +18,16 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long
parent_nip,
{
struct kprobe *p;
struct kprobe_ctlblk *kcb;
+ int bit;
+ bit = ftrace_test_recursion_trylock();
+ if (bit < 0)
+ return;
+
+ preempt_disable_notrace();
p = get_kprobe((kprobe_opcode_t *)nip);
if (unlikely(!p) || kprobe_disabled(p))
- return;
+ goto out;
kcb = get_kprobe_ctlblk();
if (kprobe_running()) {
@@ -52,6 +58,9 @@ void kprobe_ftrace_handler(unsigned long nip, unsigned long
parent_nip,
*/
__this_cpu_write(current_kprobe, NULL);
}
+out:
+ preempt_enable_notrace();
+ ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index b388e87a08bf..88466d7fb6b2 100644
---
