linux-kernel - Re: [PATCH v8 5/5] arm64: kprobes: call set_memory

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Message-ID: <22732cbe-20f8-4d1e-b086-e34d0f9bbb35@os.amperecomputing.com>
Date: Thu, 18 Sep 2025 08:05:55 -0700
From: Yang Shi <yang@...amperecomputing.com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: will@...nel.org, ryan.roberts@....com, akpm@...ux-foundation.org,
 david@...hat.com, lorenzo.stoakes@...cle.com, ardb@...nel.org,
 dev.jain@....com, scott@...amperecomputing.com, cl@...two.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH v8 5/5] arm64: kprobes: call set_memory_rox() for kprobe
 page



On 9/18/25 5:48 AM, Catalin Marinas wrote:
> On Wed, Sep 17, 2025 at 12:02:11PM -0700, Yang Shi wrote:
>> The kprobe page is allocated by execmem allocator with ROX permission.
>> It needs to call set_memory_rox() to set proper permission for the
>> direct map too. It was missed.
>>
>> And the set_memory_rox() guarantees the direct map will be split if it
>> needs so that set_direct_map calls in vfree() won't fail.
>>
>> Fixes: 10d5e97c1bf8 ("arm64: use PAGE_KERNEL_ROX directly in alloc_insn_page")
>> Signed-off-by: Yang Shi <yang@...amperecomputing.com>
>> ---
>>   arch/arm64/kernel/probes/kprobes.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/arch/arm64/kernel/probes/kprobes.c b/arch/arm64/kernel/probes/kprobes.c
>> index 0c5d408afd95..c4f8c4750f1e 100644
>> --- a/arch/arm64/kernel/probes/kprobes.c
>> +++ b/arch/arm64/kernel/probes/kprobes.c
>> @@ -10,6 +10,7 @@
>>   
>>   #define pr_fmt(fmt) "kprobes: " fmt
>>   
>> +#include <linux/execmem.h>
>>   #include <linux/extable.h>
>>   #include <linux/kasan.h>
>>   #include <linux/kernel.h>
>> @@ -41,6 +42,17 @@ DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
>>   static void __kprobes
>>   post_kprobe_handler(struct kprobe *, struct kprobe_ctlblk *, struct pt_regs *);
>>   
>> +void *alloc_insn_page(void)
>> +{
>> +	void *page;
> Nit: I'd call this 'addr'. 'page' makes me think of a struct page.

Sure.

>
>> +
>> +	page = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
>> +	if (!page)
>> +		return NULL;
>> +	set_memory_rox((unsigned long)page, 1);
> It's unfortunate that we change the attributes of the ROX vmap first to
> RO, then to back to ROX so that we get the linear map changed. Maybe
> factor out some of the code in change_memory_common() to only change the
> linear map.

I want to make sure I understand you correctly, you meant 
set_memory_rox() should do:

change linear map to RO (call a new helper, for example, 
set_direct_map_ro())
change vmap to ROX (call change_memory_common())

Is it correct?

If so set_memory_ro() should do the similar thing.

And I think we should have the cleanup patch separate from this bug fix 
patch because the bug fix patch should be applied to -stable release 
too. Keeping it simpler makes the backport easier.

Shall I squash the cleanup patch into patch #1?

Thanks,
Yang

>
> Otherwise it looks fine.
>