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    Subject[PATCH 05/11 v3] kprobes/ftrace: Add recursion protection to the ftrace callback
    From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

    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/20201028115613.140212174@goodmis.org

    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Guo Ren <guoren@kernel.org>
    Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
    Cc: Helge Deller <deller@gmx.de>
    Cc: Michael Ellerman <mpe@ellerman.id.au>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Heiko Carstens <hca@linux.ibm.com>
    Cc: Vasily Gorbik <gor@linux.ibm.com>
    Cc: Christian Borntraeger <borntraeger@de.ibm.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: x86@kernel.org
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Cc: "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>
    Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
    Cc: "David S. Miller" <davem@davemloft.net>
    Cc: linux-csky@vger.kernel.org
    Cc: linux-parisc@vger.kernel.org
    Cc: linuxppc-dev@lists.ozlabs.org
    Cc: linux-s390@vger.kernel.org
    Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
    ---

    Changes since v2:

    - Move get_kprobe() into preempt disabled sections for various archs


    arch/csky/kernel/probes/ftrace.c | 12 ++++++++++--
    arch/parisc/kernel/ftrace.c | 16 +++++++++++++---
    arch/powerpc/kernel/kprobes-ftrace.c | 11 ++++++++++-
    arch/s390/kernel/ftrace.c | 16 +++++++++++++---
    arch/x86/kernel/kprobes/ftrace.c | 12 ++++++++++--
    5 files changed, 56 insertions(+), 11 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..13d85042810a 100644
    --- a/arch/parisc/kernel/ftrace.c
    +++ b/arch/parisc/kernel/ftrace.c
    @@ -207,14 +207,21 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
    struct ftrace_ops *ops, struct pt_regs *regs)
    {
    struct kprobe_ctlblk *kcb;
    - struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip);
    + struct kprobe *p;
    + int bit;

    - if (unlikely(!p) || kprobe_disabled(p))
    + bit = ftrace_test_recursion_trylock();
    + if (bit < 0)
    return;

    + preempt_disable_notrace();
    + 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 +242,9 @@ 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..8f31c726537a 100644
    --- a/arch/s390/kernel/ftrace.c
    +++ b/arch/s390/kernel/ftrace.c
    @@ -201,14 +201,21 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
    struct ftrace_ops *ops, struct pt_regs *regs)
    {
    struct kprobe_ctlblk *kcb;
    - struct kprobe *p = get_kprobe((kprobe_opcode_t *)ip);
    + struct kprobe *p;
    + int bit;

    - if (unlikely(!p) || kprobe_disabled(p))
    + bit = ftrace_test_recursion_trylock();
    + if (bit < 0)
    return;

    + preempt_disable_notrace();
    + 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);
    @@ -228,6 +235,9 @@ 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/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
    index 681a4b36e9bb..a40a6cdfcca3 100644
    --- a/arch/x86/kernel/kprobes/ftrace.c
    +++ b/arch/x86/kernel/kprobes/ftrace.c
    @@ -18,11 +18,16 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
    {
    struct kprobe *p;
    struct kprobe_ctlblk *kcb;
    + int bit;

    - /* 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 (unlikely(!p) || kprobe_disabled(p))
    - return;
    + goto out;

    kcb = get_kprobe_ctlblk();
    if (kprobe_running()) {
    @@ -52,6 +57,9 @@ 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);

    --
    2.28.0

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