Hi Sven,
On Wed, 06 Sep 2023 08:49:11 +0200
Sven Schnelle <svens@xxxxxxxxxxxxx> wrote:
> Hi Masami,
>
> Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> writes:
>
> > Thus, we need to ensure that the ftrace_regs which is saved in the ftrace
> > *without* FTRACE_WITH_REGS flags, can be used for hooking the function
> > return. I saw;
> >
> > void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
> > {
> > rh->ret_addr = regs->gprs[14];
> > rh->frame = regs->gprs[15];
> >
> > /* Replace the return addr with trampoline addr */
> > regs->gprs[14] = (unsigned long)&arch_rethook_trampoline;
> > }
> >
> > gprs[15] is a stack pointer, so it is saved in ftrace_regs too, but what about
> > gprs[14]? (I guess it is a link register)
> > We need to read the gprs[14] and ensure that is restored to gpr14 when the
> > ftrace is exit even without FTRACE_WITH_REGS flag.
> >
> > IOW, it is ftrace save regs/restore regs code issue. I need to check how the
> > function_graph implements it.
>
> gpr2-gpr14 are always saved in ftrace_caller/ftrace_regs_caller(),
> regardless of the FTRACE_WITH_REGS flags. The only difference is that
> without the FTRACE_WITH_REGS flag the program status word (psw) is not
> saved because collecting that is a rather expensive operation.
Thanks for checking that! So s390 will recover those saved registers
even if FTRACE_WITH_REGS flag is not set? (I wonder what is the requirement
of the ftrace_regs when returning from ftrace_call() without
FTRACE_WITH_REGS?)
>
> I used the following commands to test rethook (is that the correct
> testcase?)
>
> #!/bin/bash
> cd /sys/kernel/tracing
>
> echo 'r:icmp_rcv icmp_rcv' >kprobe_events
> echo 1 >events/kprobes/icmp_rcv/enable
> ping -c 1 127.0.0.1
> cat trace
No, the kprobe will path pt_regs to rethook.
Cna you run
echo "f:icmp_rcv%return icmp_rcv" >> dynamic_events
instead of kprobe_events?
Thank you,
>
> which gave me:
>
> ping-686 [001] ..s1. 96.890817: icmp_rcv: (ip_protocol_deliver_rcu+0x42/0x218 <- icmp_rcv)
>
> I applied the following patch on top of your patches to make it compile,
> and rethook still seems to work:
>
> commit dab51b0a5b885660630433ac89f8e64a2de0eb86
> Author: Sven Schnelle <svens@xxxxxxxxxxxxx>
> Date: Wed Sep 6 08:06:23 2023 +0200
>
> rethook wip
>
> Signed-off-by: Sven Schnelle <svens@xxxxxxxxxxxxx>
>
> diff --git a/arch/s390/kernel/rethook.c b/arch/s390/kernel/rethook.c
> index af10e6bdd34e..4e86c0a1a064 100644
> --- a/arch/s390/kernel/rethook.c
> +++ b/arch/s390/kernel/rethook.c
> @@ -3,8 +3,9 @@
> #include <linux/kprobes.h>
> #include "rethook.h"
>
> -void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
> +void arch_rethook_prepare(struct rethook_node *rh, struct ftrace_regs *fregs, bool mcount)
> {
> + struct pt_regs *regs = (struct pt_regs *)fregs;
> rh->ret_addr = regs->gprs[14];
> rh->frame = regs->gprs[15];
>
> @@ -13,10 +14,11 @@ void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mc
> }
> NOKPROBE_SYMBOL(arch_rethook_prepare);
>
> -void arch_rethook_fixup_return(struct pt_regs *regs,
> +void arch_rethook_fixup_return(struct ftrace_regs *fregs,
> unsigned long correct_ret_addr)
> {
> /* Replace fake return address with real one. */
> + struct pt_regs *regs = (struct pt_regs *)fregs;
> regs->gprs[14] = correct_ret_addr;
> }
> NOKPROBE_SYMBOL(arch_rethook_fixup_return);
> @@ -24,9 +26,9 @@ NOKPROBE_SYMBOL(arch_rethook_fixup_return);
> /*
> * Called from arch_rethook_trampoline
> */
> -unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs)
> +unsigned long arch_rethook_trampoline_callback(struct ftrace_regs *fregs)
> {
> - return rethook_trampoline_handler(regs, regs->gprs[15]);
> + return rethook_trampoline_handler(fregs, fregs->regs.gprs[15]);
> }
> NOKPROBE_SYMBOL(arch_rethook_trampoline_callback);
>
> diff --git a/arch/s390/kernel/rethook.h b/arch/s390/kernel/rethook.h
> index 32f069eed3f3..0fe62424fc78 100644
> --- a/arch/s390/kernel/rethook.h
> +++ b/arch/s390/kernel/rethook.h
> @@ -2,6 +2,6 @@
> #ifndef __S390_RETHOOK_H
> #define __S390_RETHOOK_H
>
> -unsigned long arch_rethook_trampoline_callback(struct pt_regs *regs);
> +unsigned long arch_rethook_trampoline_callback(struct ftrace_regs *fregs);
>
> #endif
>
--
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
