Re: [PATCH v5] arm64: kprobe: Enable OPTPROBE for arm64

["liuqi (BA)" <liuqi115@huawei.com>]

On 2022/1/4 10:35, Masami Hiramatsu wrote:
> Hi Jianhua,
> 
> On Mon, 3 Jan 2022 17:03:33 +0800
> Jianhua Liu <jianhua.ljh@gmail.com> wrote:
> 
>> Hi Qi,
>> I have tested your patch on UNISOC s9863a.
>> Test case "kprobe_example & kretprobe_example" is OK.
>>
>> Two point:
>> 1. backtrace is not perfect.
>>     optprobe_common does not saved frame pointer,
>>     backtrace lacks two calls.
>> such as for dup_mm: lack copy_process-->dup_mm
>> dup_mm backtrace from your patch:
>> [  832.387066] CPU: 0 PID: 296 Comm: sh Not tainted 5.16.0-rc5+ #8
>> [  832.387078] Hardware name: Spreadtrum SP9863A-1H10 Board (DT)
>> [  832.387083] Call trace:
>> [  832.387086]  dump_backtrace+0x0/0x1e0
>> [  832.387103]  show_stack+0x24/0x30
>> [  832.387112]  dump_stack_lvl+0x68/0x84
>> [  832.387123]  dump_stack+0x18/0x34
>> [  832.387131]  handler_pre+0x40/0x50 [kprobe_example]
>> [  832.387143]  opt_pre_handler+0x84/0xc0
>> [  832.387154]  optprobe_optimized_callback+0xec/0x164
>> [  832.387164]  optprobe_common+0x70/0xc4
>> [  832.387173]  kernel_clone+0x98/0x440
>> [  832.387182]  __do_sys_clone+0x54/0x80
>> [  832.387191]  __arm64_sys_clone+0x2c/0x40
>> [  832.387199]  invoke_syscall+0x50/0x120
>> [  832.387208]  el0_svc_common.constprop.0+0x4c/0xf4
>> [  832.387217]  do_el0_svc+0x30/0x9c
>> [  832.387225]  el0_svc+0x20/0x60
>> [  832.387235]  el0t_64_sync_handler+0xe8/0xf0
>> [  832.387242]  el0t_64_sync+0x1a0/0x1a4
>>
>>
>> dup_mm backtrace from other:
>> [  173.352294] CPU: 6 PID: 309 Comm: sh Not tainted 5.16.0-rc5+ #19
>> [  173.352301] Hardware name: Spreadtrum SP9863A-1H10 Board (DT)
>> [  173.352304] Call trace:
>> [  173.352307]  dump_backtrace+0x0/0x1d4
>> [  173.352319]  show_stack+0x18/0x24
>> [  173.352326]  dump_stack_lvl+0x68/0x84
>> [  173.352333]  dump_stack+0x18/0x34
>> [  173.352338]  handler_pre+0x38/0x48 [kprobe_example]
>> [  173.352347]  opt_pre_handler+0x74/0xb0
>> [  173.352354]  optimized_callback+0x108/0x130
>> [  173.352361]  optinsn_slot+0x258/0x1000
>> [  173.352366]  dup_mm+0x4/0x4b0
>> [  173.352373]  copy_process+0x1284/0x1360
>> [  173.352378]  kernel_clone+0x5c/0x3c0
>> [  173.352384]  __do_sys_clone+0x54/0x80
>> [  173.352390]  __arm64_sys_clone+0x24/0x30
>> [  173.352396]  invoke_syscall+0x48/0x114
>> [  173.352402]  el0_svc_common.constprop.0+0x44/0xec
>> [  173.352408]  do_el0_svc+0x24/0x90
>> [  173.352413]  el0_svc+0x20/0x60
>> [  173.352420]  el0t_64_sync_handler+0xe8/0xf0
>> [  173.352427]  el0t_64_sync+0x1a0/0x1a4
> 

Hi Masami and Jianhua,

optprobe_common() is added to minize size of code in trampoline, but 
each trampoline is alloced as PAGE_SIZE, so optprobe_common() seems 
unnecessary, and will make optprobe_trampoline.S much more complicated.
How about drop optprobe_common() and use a maro to reduce duplicate code .

Thanks,
Qi
> Is the second one with your patch?
> 
>>
>> 2. The reserve memory "OPT_SLOT_SIZE - PAGE_SIZE"  is waste.
>>     kernel/kprobe.c used only one PAGE_SIZE slot memory.
> 
> Good catch!
> Qi, can you make an array (or bit map) of usage flags and
> manage the reserved memory?
> 
> #define OPT_INSN_PAGES (OPT_SLOT_SIZE/PAGE_SIZE)
> static bool insn_page_in_use[OPT_INSN_PAGES];
> 
> void *alloc_optinsn_page(void)
> {
> 	int i;
> 
> 	for (i = 0; i < OPT_INSN_PAGES; i++)
> 		if (!insn_page_in_use[i])
> 			goto found;
> 	return NULL;
> found:
> 	insn_page_in_use[i] = true;
> 	return (void *)((unsigned long)optinsn_slot + PAGE_SIZE * i);
> }
> 
> void free_optinsn_page(void *page)
> {
> 	unsigned long idx = (unsigned long)page - (unsigned long)optinsn_slot;
> 
> 	WARN_ONCE(idx & (PAGE_SIZE - 1));
> 	idx >>= PAGE_SHIFT;
> 	if (WARN_ONCE(idx >= OPT_INSN_PAGES))
> 		return;
> 	insn_page_in_use[idx] = false;
> }
> 
> Thank you,
> 
> 
> 
>