linux-kernel - Re: [PATCH 01/11] Initialize the mapping of KASan shadow memory

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Message-ID: <B8AC3E80E903784988AB3003E3E97330C005CCBC@dggemm510-mbx.china.huawei.com>
Date:   Thu, 19 Oct 2017 06:52:54 +0000
From:   "Liuwenliang (Lamb)" <liuwenliang@...wei.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
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CC:     "glider@...gle.com" <glider@...gle.com>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "opendmb@...il.com" <opendmb@...il.com>,
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        <linux-arm-kernel@...ts.infradead.org>,
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        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
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        Jiazhenghua <jiazhenghua@...wei.com>,
        Dailei <dylix.dailei@...wei.com>,
        Zengweilin <zengweilin@...wei.com>,
        Heshaoliang <heshaoliang@...wei.com>
Subject: Re: [PATCH 01/11] Initialize the mapping of KASan shadow memory

On 2017.10.12 7:43AM  Dmitry Osipenko [mailto:digetx@...il.com] wrote:
>Shouldn't all __pgprot's contain L_PTE_MT_WRITETHROUGH ?
>
>[...]
>
>--
>Dmitry

Thanks for your review. I'm sorry that my replay is so late.

I don't think L_PTE_MT_WRITETHROUGH is need for all arm soc. So I think kasan's
mapping can use PAGE_KERNEL which can be initialized for different arm soc and 
__pgprot(pgprot_val(PAGE_KERNEL) | L_PTE_RDONLY)).

I don't think the mapping table flags in kasan_early_init need be changed because of the follow reason:
1) PAGE_KERNEL can't be used in early_kasan_init because the pgprot_kernel which is used to define 
  PAGE_KERNEL doesn't be initialized. 

2) all of the kasan shadow's mapping table is going to be created again in kasan_init function.


All what I say is: I think only the mapping table flags in kasan_init function need to be changed into PAGE_KERNEL 
or  __pgprot(pgprot_val(PAGE_KERNEL) | L_PTE_RDONLY)). 

Here is the code, I has already tested:
--- a/arch/arm/mm/kasan_init.c
+++ b/arch/arm/mm/kasan_init.c
@@ -124,7 +124,7 @@ pte_t * __meminit kasan_pte_populate(pmd_t *pmd, unsigned long addr, int node)
                void *p = kasan_alloc_block(PAGE_SIZE, node);
                if (!p)
                        return NULL;
-           entry = pfn_pte(virt_to_pfn(p), __pgprot(_L_PTE_DEFAULT | L_PTE_DIRTY | L_PTE_XN));
+         entry = pfn_pte(virt_to_pfn(p), __pgprot(pgprot_val(PAGE_KERNEL)));
                set_pte_at(&init_mm, addr, pte, entry);
        }
        return pte;
@@ -253,7 +254,7 @@ void __init kasan_init(void)
                 set_pte_at(&init_mm, KASAN_SHADOW_START + i*PAGE_SIZE,
                         &kasan_zero_pte[i], pfn_pte(
                                 virt_to_pfn(kasan_zero_page),
-                                __pgprot(_L_PTE_DEFAULT | L_PTE_DIRTY | L_PTE_XN | L_PTE_RDONLY)));
+                         __pgprot(pgprot_val(PAGE_KERNEL) | L_PTE_RDONLY)));
        memset(kasan_zero_page, 0, PAGE_SIZE);
        cpu_set_ttbr0(orig_ttbr0);
        flush_cache_all();