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

[Masami Hiramatsu <mhiramat@kernel.org>]

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

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,




-- 
Masami Hiramatsu <mhiramat@kernel.org>