linux-kernel - Re: [PATCH v2 5/5] x86/kasan: Populate shadow for shared chunk of the CPU entry area

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Message-ID: <Y3Ja33LyShqjvmQZ@hirez.programming.kicks-ass.net>
Date:   Mon, 14 Nov 2022 16:12:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        syzbot+ffb4f000dc2872c93f62@...kaller.appspotmail.com,
        syzbot+8cdd16fd5a6c0565e227@...kaller.appspotmail.com
Subject: Re: [PATCH v2 5/5] x86/kasan: Populate shadow for shared chunk of
 the CPU entry area

On Mon, Nov 14, 2022 at 05:44:00PM +0300, Andrey Ryabinin wrote:
> Going back kasan_populate_shadow() seems like safer and easier choice.
> The only disadvantage of it that we might waste 1 page, which is not
> much compared to the KASAN memory overhead.

So the below delta?

---
--- a/arch/x86/mm/kasan_init_64.c
+++ b/arch/x86/mm/kasan_init_64.c
@@ -388,7 +388,7 @@ void __init kasan_init(void)
 	shadow_cea_end = kasan_mem_to_shadow_align_up(CPU_ENTRY_AREA_BASE +
 						      CPU_ENTRY_AREA_MAP_SIZE);
 
-	kasan_populate_early_shadow(
+	kasan_populate_shadow(
 		kasan_mem_to_shadow((void *)PAGE_OFFSET + MAXMEM),
 		kasan_mem_to_shadow((void *)VMALLOC_START));