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From: Andrey Ryabinin <ryabinin.a.a@gmail.com>
To: "Yin, Fengwei" <fengwei.yin@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	kernel test robot <yujie.liu@intel.com>
Cc: Seth Jenkins <sethjenkins@google.com>,
	Kees Cook <keescook@chromium.org>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	Alexander Potapenko <glider@google.com>,
	Andrey Konovalov <andreyknvl@gmail.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	kasan-dev@googlegroups.com, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH] x86/kasan: map shadow for percpu pages on demand
Date: Fri, 28 Oct 2022 17:20:22 +0300	[thread overview]
Message-ID: <c6fbc75a-4e8c-05f4-c1d9-53693a7c604f@gmail.com> (raw)
In-Reply-To: <3a372c25-7ce1-e931-8d7e-a2e14b82c8f0@intel.com>



On 10/28/22 05:51, Yin, Fengwei wrote:
> Hi Andrey,
> 

>>  void __init kasan_init(void)
>>  {
>>  	int i;
>> @@ -393,9 +405,6 @@ void __init kasan_init(void)
>>  		kasan_mem_to_shadow((void *)VMALLOC_END + 1),
>>  		shadow_cpu_entry_begin);
>>  
>> -	kasan_populate_shadow((unsigned long)shadow_cpu_entry_begin,
>> -			      (unsigned long)shadow_cpu_entry_end, 0);
>> -
> There will be address in the range (shadow_cpu_entry_begin, shadow_cpu_entry_end)
> which has no KASAN shadow mapping populated after the patch. Not sure whether
> it could be a problem. Thanks.
> 


This shouldn't be a problem. It's vital to have shadow *only* for addresses with mapped memory.
Shadow address accessed only if the address itself accessed. So the difference between not having shadow
for address with no mapping vs having it, is whether we crash on access to KASAN shadow or crash few
instructions later on access to the address itself.

  reply	other threads:[~2022-10-28 14:20 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-25  4:54 [tip:x86/mm] [x86/mm] 1248fb6a82: Kernel_panic-not_syncing:kasan_populate_pmd:Failed_to_allocate_page kernel test robot
2022-10-25 10:33 ` Peter Zijlstra
2022-10-25 14:14   ` Yin, Fengwei
2022-10-25 15:39   ` Andrey Ryabinin
2022-10-27 10:02     ` Yujie Liu
2022-10-27 10:13       ` Peter Zijlstra
2022-10-27 15:12     ` Dave Hansen
2022-10-27 21:31       ` [PATCH] x86/kasan: map shadow for percpu pages on demand Andrey Ryabinin
2022-10-28  2:51         ` Yin, Fengwei
2022-10-28 14:20           ` Andrey Ryabinin [this message]
2022-10-31  0:15             ` Yin, Fengwei
2022-10-27 21:35       ` [tip:x86/mm] [x86/mm] 1248fb6a82: Kernel_panic-not_syncing:kasan_populate_pmd:Failed_to_allocate_page Andrey Ryabinin
2022-10-28  6:43 ` [tip: x86/mm] x86/kasan: Map shadow for percpu pages on demand tip-bot2 for Andrey Ryabinin
2022-12-17 18:55 ` tip-bot2 for Andrey Ryabinin

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