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Date: Tue, 7 Jun 2016 19:28:36 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: David Long <dave.long@...aro.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
Huang Shijie <shijie.huang@....com>,
James Morse <james.morse@....com>,
Marc Zyngier <marc.zyngier@....com>,
Pratyush Anand <panand@...hat.com>,
Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
Will Deacon <will.deacon@....com>,
William Cohen <wcohen@...hat.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Steve Capper <steve.capper@...aro.org>,
Li Bin <huawei.libin@...wei.com>,
Adam Buchbinder <adam.buchbinder@...il.com>,
Alex Bennée <alex.bennee@...aro.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andrey Ryabinin <ryabinin.a.a@...il.com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Christoffer Dall <christoffer.dall@...aro.org>,
Daniel Thompson <daniel.thompson@...aro.org>,
Dave P Martin <Dave.Martin@....com>,
Jens Wiklander <jens.wiklander@...aro.org>,
Jisheng Zhang <jszhang@...vell.com>,
John Blackwood <john.blackwood@...r.com>,
Mark Rutland <mark.rutland@....com>,
Petr Mladek <pmladek@...e.com>,
Robin Murphy <robin.murphy@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Vladimir Murzin <Vladimir.Murzin@....com>,
Yang Shi <yang.shi@...aro.org>,
Zi Shen Lim <zlim.lnx@...il.com>,
yalin wang <yalin.wang2010@...il.com>,
Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v13 09/10] arm64: Add kernel return probes support
(kretprobes)
On Thu, 2 Jun 2016 23:26:23 -0400
David Long <dave.long@...aro.org> wrote:
> From: Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>
>
> The pre-handler of this special 'trampoline' kprobe executes the return
> probe handler functions and restores original return address in ELR_EL1.
> This way the saved pt_regs still hold the original register context to be
> carried back to the probed kernel function.
>
> Signed-off-by: Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>
> Signed-off-by: David A. Long <dave.long@...aro.org>
> ---
> arch/arm64/Kconfig | 1 +
> arch/arm64/kernel/kprobes.c | 75 ++++++++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 75 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 5496b75..47989eb 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -89,6 +89,7 @@ config ARM64
> select HAVE_RCU_TABLE_FREE
> select HAVE_SYSCALL_TRACEPOINTS
> select HAVE_KPROBES
> + select HAVE_KRETPROBES if HAVE_KPROBES
> select IOMMU_DMA if IOMMU_SUPPORT
> select IRQ_DOMAIN
> select IRQ_FORCED_THREADING
> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c
> index b35f76f..c116904 100644
> --- a/arch/arm64/kernel/kprobes.c
> +++ b/arch/arm64/kernel/kprobes.c
> @@ -577,7 +577,80 @@ bool arch_within_kprobe_blacklist(unsigned long addr)
>
> void __kprobes __used *trampoline_probe_handler(struct pt_regs *regs)
> {
> - return NULL;
> + struct kretprobe_instance *ri = NULL;
> + struct hlist_head *head, empty_rp;
> + struct hlist_node *tmp;
> + unsigned long flags, orig_ret_addr = 0;
> + unsigned long trampoline_address =
> + (unsigned long)&kretprobe_trampoline;
> +
> + INIT_HLIST_HEAD(&empty_rp);
> + kretprobe_hash_lock(current, &head, &flags);
> +
> + /*
> + * It is possible to have multiple instances associated with a given
> + * task either because multiple functions in the call path have
> + * a return probe installed on them, and/or more than one return
> + * probe was registered for a target function.
> + *
> + * We can handle this because:
> + * - instances are always inserted at the head of the list
> + * - when multiple return probes are registered for the same
> + * function, the first instance's ret_addr will point to the
> + * real return address, and all the rest will point to
> + * kretprobe_trampoline
> + */
> + hlist_for_each_entry_safe(ri, tmp, head, hlist) {
> + if (ri->task != current)
> + /* another task is sharing our hash bucket */
> + continue;
> +
> + if (ri->rp && ri->rp->handler) {
> + __this_cpu_write(current_kprobe, &ri->rp->kp);
> + get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
> + ri->rp->handler(ri, regs);
> + __this_cpu_write(current_kprobe, NULL);
> + }
> +
> + orig_ret_addr = (unsigned long)ri->ret_addr;
> + recycle_rp_inst(ri, &empty_rp);
> +
> + if (orig_ret_addr != trampoline_address)
> + /*
> + * This is the real return address. Any other
> + * instances associated with this task are for
> + * other calls deeper on the call stack
> + */
> + break;
> + }
This looks not included an improvement done by Syuhei, see
commit 737480a0d525 ("kprobes/x86: Fix the return address of multiple kretprobes")
Thank you!
> +
> + kretprobe_assert(ri, orig_ret_addr, trampoline_address);
> + /* restore the original return address */
> + instruction_pointer(regs) = orig_ret_addr;
> + reset_current_kprobe();
> + kretprobe_hash_unlock(current, &flags);
> +
> + hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
> + hlist_del(&ri->hlist);
> + kfree(ri);
> + }
> +
> + /* return 1 so that post handlers not called */
> + return (void *) orig_ret_addr;
> +}
> +
> +void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
> + struct pt_regs *regs)
> +{
> + ri->ret_addr = (kprobe_opcode_t *)regs->regs[30];
> +
> + /* replace return addr (x30) with trampoline */
> + regs->regs[30] = (long)&kretprobe_trampoline;
> +}
> +
> +int __kprobes arch_trampoline_kprobe(struct kprobe *p)
> +{
> + return 0;
> }
>
> int __init arch_init_kprobes(void)
> --
> 2.5.0
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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