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SubjectRe: [PATCH v5] arm64: kprobe: Enable OPTPROBE for arm64
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>

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