Hi Steve,
Thanks for the review.
I'll fix the typos.
On Tue, 25 Jan 2022 11:46:15 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> > + */
> > +static inline bool is_rethook_trampoline(unsigned long addr)
> > +{
> > + return addr == (unsigned long)arch_rethook_trampoline;
>
> Will this work on architectures like PPC that have strange ways of holding
> the function addresses? Or is that what the below fixup handles?
Yes, I'll use dereference_symbol_descriptor().
> > +}
> > +
> > +/* If the architecture needs a fixup the return address, implement it. */
>
> "needs to fixup the"
>
> > +void arch_rethook_fixup_return(struct pt_regs *regs,
> > + unsigned long correct_ret_addr);
> > +
> > +/* Generic trampoline handler, arch code must prepare asm stub */
> > +unsigned long rethook_trampoline_handler(struct pt_regs *regs,
> > + unsigned long frame);
> > +
> > +#ifdef CONFIG_RETHOOK
> > +void rethook_flush_task(struct task_struct *tk);
> > +#else
> > +#define rethook_flush_task(tsk) do { } while (0)
> > +#endif
> > +
> > +#endif
> > +
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 78c351e35fec..2bfabf5355b7 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1473,6 +1473,9 @@ struct task_struct {
> > #ifdef CONFIG_KRETPROBES
> > struct llist_head kretprobe_instances;
> > #endif
> > +#ifdef CONFIG_RETHOOK
> > + struct llist_head rethooks;
> > +#endif
> >
> > #ifdef CONFIG_ARCH_HAS_PARANOID_L1D_FLUSH
> > /*
> > diff --git a/kernel/exit.c b/kernel/exit.c
> > index f702a6a63686..a39a321c1f37 100644
> > --- a/kernel/exit.c
> > +++ b/kernel/exit.c
> > @@ -64,6 +64,7 @@
> > #include <linux/compat.h>
> > #include <linux/io_uring.h>
> > #include <linux/kprobes.h>
> > +#include <linux/rethook.h>
> >
> > #include <linux/uaccess.h>
> > #include <asm/unistd.h>
> > @@ -169,6 +170,7 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
> > struct task_struct *tsk = container_of(rhp, struct task_struct, rcu);
> >
> > kprobe_flush_task(tsk);
> > + rethook_flush_task(tsk);
> > perf_event_delayed_put(tsk);
> > trace_sched_process_free(tsk);
> > put_task_struct(tsk);
> > diff --git a/kernel/fork.c b/kernel/fork.c
> > index 3244cc56b697..ffae38be64c4 100644
> > --- a/kernel/fork.c
> > +++ b/kernel/fork.c
> > @@ -2282,6 +2282,9 @@ static __latent_entropy struct task_struct *copy_process(
> > #ifdef CONFIG_KRETPROBES
> > p->kretprobe_instances.first = NULL;
> > #endif
> > +#ifdef CONFIG_RETHOOK
> > + p->rethooks.first = NULL;
> > +#endif
> >
> > /*
> > * Ensure that the cgroup subsystem policies allow the new process to be
> > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> > index 23483dd474b0..4d27e56c6e76 100644
> > --- a/kernel/trace/Kconfig
> > +++ b/kernel/trace/Kconfig
> > @@ -10,6 +10,17 @@ config USER_STACKTRACE_SUPPORT
> > config NOP_TRACER
> > bool
> >
> > +config HAVE_RETHOOK
> > + bool
> > +
> > +config RETHOOK
> > + bool
> > + depends on HAVE_RETHOOK
> > + help
> > + Enable generic return hooking feature. This is an internal
> > + API, which will be used by other function-entry hooking
> > + feature like fprobe and kprobes.
>
> "features"
>
> > +
> > config HAVE_FUNCTION_TRACER
> > bool
> > help
> > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> > index 79255f9de9a4..c6f11a139eac 100644
> > --- a/kernel/trace/Makefile
> > +++ b/kernel/trace/Makefile
> > @@ -98,6 +98,7 @@ obj-$(CONFIG_UPROBE_EVENTS) += trace_uprobe.o
> > obj-$(CONFIG_BOOTTIME_TRACING) += trace_boot.o
> > obj-$(CONFIG_FTRACE_RECORD_RECURSION) += trace_recursion_record.o
> > obj-$(CONFIG_FPROBE) += fprobe.o
> > +obj-$(CONFIG_RETHOOK) += rethook.o
> >
> > obj-$(CONFIG_TRACEPOINT_BENCHMARK) += trace_benchmark.o
> >
> > diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
> > new file mode 100644
> > index 000000000000..76c9848b44a9
> > --- /dev/null
> > +++ b/kernel/trace/rethook.c
> > @@ -0,0 +1,311 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#define pr_fmt(fmt) "rethook: " fmt
> > +
> > +#include <linux/bug.h>
> > +#include <linux/kallsyms.h>
> > +#include <linux/kprobes.h>
> > +#include <linux/preempt.h>
> > +#include <linux/rethook.h>
> > +#include <linux/slab.h>
> > +#include <linux/sort.h>
> > +
> > +/* Return hook list (shadow stack by list) */
> > +
> > +/*
> > + * This function is called from delayed_put_task_struct() when a task is
> > + * dead and cleaned up to recycle any kretprobe instances associated with
> > + * this task. These left over instances represent probed functions that
> > + * have been called but will never return.
> > + */
> > +void rethook_flush_task(struct task_struct *tk)
> > +{
> > + struct rethook_node *rhn;
> > + struct llist_node *node;
> > +
> > + preempt_disable();
> > +
> > + node = __llist_del_all(&tk->rethooks);
>
> Hmm, this keeps preemption disabled for the entire walk of the list.
> Can we enable it here, and then just disable it when calling
> rethook_recycle()?
Yes, it is possible.
> > + while (node) {
> > + rhn = container_of(node, struct rethook_node, llist);
> > + node = node->next;
>
> preempt_disable();
> > + rethook_recycle(rhn);
> preempt_enable();
>
> ? I'm concerned about the latency that this can add on RT tasks.
OK, actually I just followed what the kretprobe does.
[SNIP]
> > +/* This assumes the 'tsk' is the current task or the is not running. */
>
> "or the is not running" ?
Oops, "a task which is not running"
> > +/**
> > + * rethook_find_ret_addr -- Find correct return address modified by rethook
> > + * @tsk: Target task
> > + * @frame: A frame pointer
> > + * @cur: a storage of the loop cursor llist_node pointer for next call
> > + *
> > + * Find the correct return address modified by a rethook on @tsk in unsigned
> > + * long type. If it finds the return address, this returns that address value,
> > + * or this returns 0.
>
> space
>
> > + * The @tsk must be 'current' or a task which is not running. @frame is a hint
>
> How do you know a tsk is not running? How can that be guaranteed?
There is no check yet (I expected to caller ensure it).
I'll add task_is_running() check.
> > + * to get the currect return address - which is compared with the
> > + * rethook::frame field. The @cur is a loop cursor for searching the
> > + * kretprobe return addresses on the @tsk. The '*@cur' should be NULL at the
> > + * first call, but '@cur' itself must NOT NULL.
>
> I know you state what the return value is above, but it should be stated
> (again) here. As kernel-doc should have a separate section for return
> values:
>
> * Returns found address value or zero if not found.
OK.
>
> > + */
> > +unsigned long rethook_find_ret_addr(struct task_struct *tsk, unsigned long frame,
> > + struct llist_node **cur)
> > +{
> > + struct rethook_node *rhn = NULL;
> > + unsigned long ret;
> > +
> > + if (WARN_ON_ONCE(!cur))
> > + return 0;
> > +
> > + do {
> > + ret = __rethook_find_ret_addr(tsk, cur);
> > + if (!ret)
> > + break;
> > + rhn = container_of(*cur, struct rethook_node, llist);
> > + } while (rhn->frame != frame);
> > +
> > + return ret;
> > +}
>
Thank you!
> -- Steve
>
>
> > +NOKPROBE_SYMBOL(rethook_find_ret_addr);
> > +
> > +void __weak arch_rethook_fixup_return(struct pt_regs *regs,
> > + unsigned long correct_ret_addr)
> > +{
> > + /*
> > + * Do nothing by default. If the architecture which uses a
> > + * frame pointer to record real return address on the stack,
> > + * it should fill this function to fixup the return address
> > + * so that stacktrace works from the rethook handler.
> > + */
> > +}
> > +
> > +/* This function will be called from each arch-defined trampoline. */
> > +unsigned long rethook_trampoline_handler(struct pt_regs *regs,
> > + unsigned long frame)
> > +{
> > + struct llist_node *first, *node = NULL;
> > + unsigned long correct_ret_addr;
> > + rethook_handler_t handler;
> > + struct rethook_node *rhn;
> > +
> > + correct_ret_addr = __rethook_find_ret_addr(current, &node);
> > + if (!correct_ret_addr) {
> > + pr_err("rethook: Return address not found! Maybe there is a bug in the kernel\n");
> > + BUG_ON(1);
> > + }
> > +
> > + instruction_pointer_set(regs, correct_ret_addr);
> > +
> > + /*
> > + * These loops must be protected from rethook_free_rcu() because those
> > + * are accessing 'rhn->rethook'.
> > + */
> > + preempt_disable();
> > +
> > + /*
> > + * Run the handler on the shadow stack. Do not unlink the list here because
> > + * stackdump inside the handlers needs to decode it.
> > + */
> > + first = current->rethooks.first;
> > + while (first) {
> > + rhn = container_of(first, struct rethook_node, llist);
> > + if (WARN_ON_ONCE(rhn->frame != frame))
> > + break;
> > + handler = READ_ONCE(rhn->rethook->handler);
> > + if (handler)
> > + handler(rhn, rhn->rethook->data, regs);
> > +
> > + if (first == node)
> > + break;
> > + first = first->next;
> > + }
> > +
> > + /* Fixup registers for returning to correct address. */
> > + arch_rethook_fixup_return(regs, correct_ret_addr);
> > +
> > + /* Unlink used shadow stack */
> > + first = current->rethooks.first;
> > + current->rethooks.first = node->next;
> > + node->next = NULL;
> > +
> > + while (first) {
> > + rhn = container_of(first, struct rethook_node, llist);
> > + first = first->next;
> > + rethook_recycle(rhn);
> > + }
> > + preempt_enable();
> > +
> > + return correct_ret_addr;
> > +}
> > +NOKPROBE_SYMBOL(rethook_trampoline_handler);
>
--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>
