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Subject: Re: [PATCH v2 3/5] LoongArch: Add kretprobe support
To:     Huacai Chen <chenhuacai@kernel.org>,
        Tiezhu Yang <yangtiezhu@loongson.cn>
Cc:     Masami Hiramatsu <mhiramat@kernel.org>, loongarch@lists.linux.dev,
        linux-kernel@vger.kernel.org
References: <1664326209-13995-1-git-send-email-yangtiezhu@loongson.cn>
 <1664326209-13995-4-git-send-email-yangtiezhu@loongson.cn>
 <CAAhV-H7N-N2400ivdczJrfJ9Ht12JUbOADxExF87wVPFEj_c_g@mail.gmail.com>
From:   Jinyang He <hejinyang@loongson.cn>
Message-ID: <dd3fc4ab-6bbb-2fa5-8d5e-b8206b42518c@loongson.cn>
Date:   Mon, 14 Nov 2022 14:11:13 +0800
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On 2022/11/14 下午12:43, Huacai Chen wrote:

> Hi, Tiezhu and Jinyang,
>
> On Wed, Sep 28, 2022 at 8:50 AM Tiezhu Yang <yangtiezhu@loongson.cn> wrote:
>> Use the generic kretprobe trampoline handler to add kretprobe
>> support for LoongArch.
>>
>> Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
>> ---
>>   arch/loongarch/Kconfig                     |  1 +
>>   arch/loongarch/kernel/Makefile             |  2 +-
>>   arch/loongarch/kernel/kprobes.c            | 24 ++++++++
>>   arch/loongarch/kernel/kprobes_trampoline.S | 97 ++++++++++++++++++++++++++++++
>>   4 files changed, 123 insertions(+), 1 deletion(-)
>>   create mode 100644 arch/loongarch/kernel/kprobes_trampoline.S
>>
>> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
>> index 8debd70..877be6a 100644
>> --- a/arch/loongarch/Kconfig
>> +++ b/arch/loongarch/Kconfig
>> @@ -95,6 +95,7 @@ config LOONGARCH
>>          select HAVE_IRQ_EXIT_ON_IRQ_STACK
>>          select HAVE_IRQ_TIME_ACCOUNTING
>>          select HAVE_KPROBES
>> +       select HAVE_KRETPROBES
>>          select HAVE_MOD_ARCH_SPECIFIC
>>          select HAVE_NMI
>>          select HAVE_PCI
>> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
>> index ff98d8a..48f50607 100644
>> --- a/arch/loongarch/kernel/Makefile
>> +++ b/arch/loongarch/kernel/Makefile
>> @@ -33,6 +33,6 @@ obj-$(CONFIG_UNWINDER_PROLOGUE) += unwind_prologue.o
>>
>>   obj-$(CONFIG_PERF_EVENTS)      += perf_event.o perf_regs.o
>>
>> -obj-$(CONFIG_KPROBES)          += kprobes.o
>> +obj-$(CONFIG_KPROBES)          += kprobes.o kprobes_trampoline.o
>>
>>   CPPFLAGS_vmlinux.lds           := $(KBUILD_CFLAGS)
>> diff --git a/arch/loongarch/kernel/kprobes.c b/arch/loongarch/kernel/kprobes.c
>> index c11f6e0..ca3f1dc 100644
>> --- a/arch/loongarch/kernel/kprobes.c
>> +++ b/arch/loongarch/kernel/kprobes.c
>> @@ -306,6 +306,30 @@ int __init arch_populate_kprobe_blacklist(void)
>>                                           (unsigned long)__irqentry_text_end);
>>   }
>>
>> +/* Called from __kretprobe_trampoline */
>> +void __used *trampoline_probe_handler(struct pt_regs *regs)
>> +{
>> +       return (void *)kretprobe_trampoline_handler(regs, NULL);
>> +}
>> +NOKPROBE_SYMBOL(trampoline_probe_handler);
>> +
>> +void arch_prepare_kretprobe(struct kretprobe_instance *ri,
>> +                           struct pt_regs *regs)
>> +{
>> +       ri->ret_addr = (kprobe_opcode_t *)regs->regs[1];
>> +       ri->fp = NULL;
>> +
>> +       /* Replace the return addr with trampoline addr */
>> +       regs->regs[1] = (unsigned long)&__kretprobe_trampoline;
>> +}
>> +NOKPROBE_SYMBOL(arch_prepare_kretprobe);
>> +
>> +int arch_trampoline_kprobe(struct kprobe *p)
>> +{
>> +       return 0;
>> +}
>> +NOKPROBE_SYMBOL(arch_trampoline_kprobe);
>> +
>>   int __init arch_init_kprobes(void)
>>   {
>>          return 0;
>> diff --git a/arch/loongarch/kernel/kprobes_trampoline.S b/arch/loongarch/kernel/kprobes_trampoline.S
>> new file mode 100644
>> index 0000000..9888ab8
>> --- /dev/null
>> +++ b/arch/loongarch/kernel/kprobes_trampoline.S
>> @@ -0,0 +1,97 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +#include <linux/linkage.h>
>> +#include <asm/stackframe.h>
>> +
>> +       .text
>> +
>> +       .macro save_all_base_regs
>> +       cfi_st  zero, PT_R0
>> +       cfi_st  ra, PT_R1
>> +       cfi_st  tp, PT_R2
>> +       cfi_st  a0, PT_R4
>> +       cfi_st  a1, PT_R5
>> +       cfi_st  a2, PT_R6
>> +       cfi_st  a3, PT_R7
>> +       cfi_st  a4, PT_R8
>> +       cfi_st  a5, PT_R9
>> +       cfi_st  a6, PT_R10
>> +       cfi_st  a7, PT_R11
>> +       cfi_st  t0, PT_R12
>> +       cfi_st  t1, PT_R13
>> +       cfi_st  t2, PT_R14
>> +       cfi_st  t3, PT_R15
>> +       cfi_st  t4, PT_R16
>> +       cfi_st  t5, PT_R17
>> +       cfi_st  t6, PT_R18
>> +       cfi_st  t7, PT_R19
>> +       cfi_st  t8, PT_R20
>> +       cfi_st  u0, PT_R21
>> +       cfi_st  fp, PT_R22
>> +       cfi_st  s0, PT_R23
>> +       cfi_st  s1, PT_R24
>> +       cfi_st  s2, PT_R25
>> +       cfi_st  s3, PT_R26
>> +       cfi_st  s4, PT_R27
>> +       cfi_st  s5, PT_R28
>> +       cfi_st  s6, PT_R29
>> +       cfi_st  s7, PT_R30
>> +       cfi_st  s8, PT_R31
>> +       addi.d  t0, sp, PT_SIZE
>> +       LONG_S  t0, sp, PT_R3
>> +       csrrd   t0, LOONGARCH_CSR_CRMD
>> +       andi    t0, t0, 0x7 /* extract bit[1:0] PLV, bit[2] IE */
>> +       LONG_S  t0, sp, PT_PRMD
>> +       .endm
>> +
>> +       .macro restore_all_base_regs
>> +       cfi_ld  zero, PT_R0
>> +       cfi_ld  tp, PT_R2
>> +       cfi_ld  a0, PT_R4
>> +       cfi_ld  a1, PT_R5
>> +       cfi_ld  a2, PT_R6
>> +       cfi_ld  a3, PT_R7
>> +       cfi_ld  a4, PT_R8
>> +       cfi_ld  a5, PT_R9
>> +       cfi_ld  a6, PT_R10
>> +       cfi_ld  a7, PT_R11
>> +       cfi_ld  t0, PT_R12
>> +       cfi_ld  t1, PT_R13
>> +       cfi_ld  t2, PT_R14
>> +       cfi_ld  t3, PT_R15
>> +       cfi_ld  t4, PT_R16
>> +       cfi_ld  t5, PT_R17
>> +       cfi_ld  t6, PT_R18
>> +       cfi_ld  t7, PT_R19
>> +       cfi_ld  t8, PT_R20
>> +       cfi_ld  u0, PT_R21
>> +       cfi_ld  fp, PT_R22
>> +       cfi_ld  s0, PT_R23
>> +       cfi_ld  s1, PT_R24
>> +       cfi_ld  s2, PT_R25
>> +       cfi_ld  s3, PT_R26
>> +       cfi_ld  s4, PT_R27
>> +       cfi_ld  s5, PT_R28
>> +       cfi_ld  s6, PT_R29
>> +       cfi_ld  s7, PT_R30
>> +       cfi_ld  s8, PT_R31
>> +       LONG_L  t0, sp, PT_PRMD
>> +       li.d    t1, 0x7 /* mask bit[1:0] PLV, bit[2] IE */
>> +       csrxchg t0, t1, LOONGARCH_CSR_CRMD
>> +       .endm
> Do you think we need to save and restore all regs here?
>
> Huacai

Hi, Huacai,


Note that it is not function context. In the original kprobe design, it is
triggered by 'break' and then trap into exception with all pt_regs saved.
The all pt_regs will be visible to the user. So I think in this version
we should also support all regs to user. BTW, due to all exceptions is
trapped by 'break' something in pt_regs is not needed, like estat,
badvaddr and so on.


Thanks,

Jinyang

>> +
>> +SYM_CODE_START(__kretprobe_trampoline)
>> +       addi.d  sp, sp, -PT_SIZE
>> +       save_all_base_regs
>> +
>> +       move a0, sp /* pt_regs */
>> +
>> +       bl trampoline_probe_handler
>> +
>> +       /* use the result as the return-address */
>> +       move ra, a0
>> +
>> +       restore_all_base_regs
>> +       addi.d  sp, sp, PT_SIZE
>> +
>> +       jr ra
>> +SYM_CODE_END(__kretprobe_trampoline)
>> --
>> 2.1.0
>>
>>