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// SPDX-License-Identifier: GPL-2.0-only
/*
* PowerPC implementation of rethook. This depends on kprobes.
*/
#include <linux/kprobes.h>
#include <linux/rethook.h>
/*
* Function return trampoline:
* - init_kprobes() establishes a probepoint here
* - When the probed function returns, this probe
* causes the handlers to fire
*/
asm(".global arch_rethook_trampoline\n"
".type arch_rethook_trampoline, @function\n"
"arch_rethook_trampoline:\n"
"nop\n"
"blr\n"
".size arch_rethook_trampoline, .-arch_rethook_trampoline\n");
/*
* Called when the probe at kretprobe trampoline is hit
*/
static int trampoline_rethook_handler(struct kprobe *p, struct pt_regs *regs)
{
return !rethook_trampoline_handler(regs, regs->gpr[1]);
}
NOKPROBE_SYMBOL(trampoline_rethook_handler);
void arch_rethook_prepare(struct rethook_node *rh, struct pt_regs *regs, bool mcount)
{
rh->ret_addr = regs->link;
rh->frame = regs->gpr[1];
/* Replace the return addr with trampoline addr */
regs->link = (unsigned long)arch_rethook_trampoline;
}
NOKPROBE_SYMBOL(arch_rethook_prepare);
/* This is called from rethook_trampoline_handler(). */
void arch_rethook_fixup_return(struct pt_regs *regs, unsigned long orig_ret_address)
{
/*
* We get here through one of two paths:
* 1. by taking a trap -> kprobe_handler() -> here
* 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here
*
* When going back through (1), we need regs->nip to be setup properly
* as it is used to determine the return address from the trap.
* For (2), since nip is not honoured with optprobes, we instead setup
* the link register properly so that the subsequent 'blr' in
* arch_rethook_trampoline jumps back to the right instruction.
*
* For nip, we should set the address to the previous instruction since
* we end up emulating it in kprobe_handler(), which increments the nip
* again.
*/
regs_set_return_ip(regs, orig_ret_address - 4);
regs->link = orig_ret_address;
}
NOKPROBE_SYMBOL(arch_rethook_fixup_return);
static struct kprobe trampoline_p = {
.addr = (kprobe_opcode_t *) &arch_rethook_trampoline,
.pre_handler = trampoline_rethook_handler
};
/* rethook initializer */
int __init arch_init_kprobes(void)
{
return register_kprobe(&trampoline_p);
}
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