linux-kernel - Re: [PATCH] arm64: uprobes: Optimize cache flushes for xol slot

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Message-ID: <41fdfc47-4161-d2e4-6528-4079b660424f@huawei.com>
Date: Fri, 20 Sep 2024 16:58:31 +0800
From: "Liao, Chang" <liaochang1@...wei.com>
To: Oleg Nesterov <oleg@...hat.com>
CC: <mhiramat@...nel.org>, <peterz@...radead.org>, <catalin.marinas@....com>,
	<will@...nel.org>, <mark.rutland@....com>, <linux-kernel@...r.kernel.org>,
	<linux-trace-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: uprobes: Optimize cache flushes for xol slot



在 2024/9/19 22:18, Oleg Nesterov 写道:
> On 09/19, Liao Chang wrote:
>>
>> --- a/arch/arm64/kernel/probes/uprobes.c
>> +++ b/arch/arm64/kernel/probes/uprobes.c
>> @@ -17,12 +17,16 @@ void arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
>>  	void *xol_page_kaddr = kmap_atomic(page);
>>  	void *dst = xol_page_kaddr + (vaddr & ~PAGE_MASK);
>>
>> +	if (!memcmp(dst, src, len))
>> +		goto done;
> 
> can't really comment, I know nothing about arm64...
> 
> but don't we need to change __create_xol_area()
> 
> 	-	area->page = alloc_page(GFP_HIGHUSER);
> 	+	area->page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
> 
> to avoid the false positives?

Indeed, it would be safer.

Could we tolerate these false positives? Even if the page are not reset
to zero bits, if the existing bits are the same as the instruction being
copied, it still can execute the correct instruction.

> 
> Oleg.
> 
> 

-- 
BR
Liao, Chang