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Date: Sat, 24 Feb 2018 14:28:26 +0000
From: "Liuwenliang (Abbott Liu)" <liuwenliang@...wei.com>
To: Russell King - ARM Linux <linux@...linux.org.uk>
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Subject: Re: [PATCH 01/11] Initialize the mapping of KASan shadow memory
On Oct 19, 2017 at 19:09, Russell King - ARM Linux [mailto:linux@...linux.org.uk] wrote:
>On Wed, Oct 11, 2017 at 04:22:17PM +0800, Abbott Liu wrote:
>> +#else
>> +#define pud_populate(mm,pmd,pte) do { } while (0)
>> +#endif
>
>Please explain this change - we don't have a "pud" as far as the rest of
>the Linux MM layer is concerned, so why do we need it for kasan?
>
>I suspect it comes from the way we wrap up the page tables - where ARM
>does it one way (because it has to) vs the subsequently merged method
>which is completely upside down to what ARMs doing, and therefore is
>totally incompatible and impossible to fit in with our way.
We will use pud_polulate in kasan_populate_zero_shadow function.
....
>> obj-$(CONFIG_CACHE_TAUROS2) += cache-tauros2.o
>> +
>> +KASAN_SANITIZE_kasan_init.o := n
>> +obj-$(CONFIG_KASAN) += kasan_init.o
>
>Why is this placed in the middle of the cache object listing?
Sorry, I will place this at the end of the arch/arm/mm/Makefile.
>> +
>> +
>> obj-$(CONFIG_CACHE_UNIPHIER) += cache-uniphier.o
...
>> +pgd_t * __meminit kasan_pgd_populate(unsigned long addr, int node)
>> +{
>> + pgd_t *pgd = pgd_offset_k(addr);
>> + if (pgd_none(*pgd)) {
>> + void *p = kasan_alloc_block(PAGE_SIZE, node);
>> + if (!p)
>> + return NULL;
>> + pgd_populate(&init_mm, pgd, p);
>> + }
>> + return pgd;
>> +}
>This all looks wrong - you are aware that on non-LPAE platforms, there
>is only a _two_ level page table - the top level page table is 16K in
>size, and each _individual_ lower level page table is actually 1024
>bytes, but we do some special handling in the kernel to combine two
>together. It looks to me that you allocate memory for each Linux-
>abstracted page table level whether the hardware needs it or not.
You are right. If non-LPAE platform check if(pgd_none(*pgd)) true,
void *p = kasan_alloc_block(PAGE_SIZE, node) alloc space is not enough.
But the the function kasan_pgd_populate only used in :
Kasan_init-> create_mapping-> kasan_pgd_populate , so when non-LPAE platform
the if (pgd_none(*pgd)) always false.
But I also think change those code is much better :
if (IS_ENABLED(CONFIG_ARM_LPAE)) {
p = kasan_alloc_block(PAGE_SIZE, node);
} else {
/* non-LPAE need 16K for first level pagetabe*/
p = kasan_alloc_block(PAGE_SIZE*4, node);
}
>Is there any reason why the pre-existing "create_mapping()" function
>can't be used, and you've had to rewrite that code here?
Two reason:
1) Here create_mapping can dynamic alloc phys memory space for mapping to virtual space
Which from start to end, but the create_mapping in arch/arm/mm/mmu.c can't.
2) for LPAE, create_mapping need alloc pgd which we need use virtual space below 0xc0000000,
here create_mapping can alloc pgd, but create_mapping in arch/arm/mm/mmu.c can't.
>> +
>> +static int __init create_mapping(unsigned long start, unsigned long end, int node)
>> +{
>> + unsigned long addr = start;
>> + pgd_t *pgd;
>> + pud_t *pud;
>> + pmd_t *pmd;
>> + pte_t *pte;
>
>A blank line would help between the auto variables and the code of the
>function.
Ok, I will add blank line in new version.
>> + pr_info("populating shadow for %lx, %lx\n", start, end);
>
>Blank line here too please.
Ok, I will add blank line in new version.
>> + for (; addr < end; addr += PAGE_SIZE) {
>> + pgd = kasan_pgd_populate(addr, node);
>> + if (!pgd)
>> + return -ENOMEM;
...
>> +void __init kasan_init(void)
>> +{
>> + struct memblock_region *reg;
>> + u64 orig_ttbr0;
>> +
>> + orig_ttbr0 = cpu_get_ttbr(0);
>> +
>> +#ifdef CONFIG_ARM_LPAE
>> + memcpy(tmp_pmd_table, pgd_page_vaddr(*pgd_offset_k(KASAN_SHADOW_START)), sizeof(tmp_pmd_table));
>> + memcpy(tmp_page_table, swapper_pg_dir, sizeof(tmp_page_table));
>> + set_pgd(&tmp_page_table[pgd_index(KASAN_SHADOW_START)], __pgd(__pa(tmp_pmd_table) | PMD_TYPE_TABLE | L_PGD_SWAPPER));
>> + cpu_set_ttbr0(__pa(tmp_page_table));
>> +#else
>> + memcpy(tmp_page_table, swapper_pg_dir, sizeof(tmp_page_table));
>> + cpu_set_ttbr0(__pa(tmp_page_table));
>> +#endif
>> + flush_cache_all();
>> + local_flush_bp_all();
>> + local_flush_tlb_all();
>What are you trying to achieve with all this complexity? Some comments
>might be useful, especially for those of us who don't know the internals
>of kasan.
OK, I will add some comments in kasan_init function in new version.
...
>> + for_each_memblock(memory, reg) {
>> + void *start = __va(reg->base);
>> + void *end = __va(reg->base + reg->size);
>
>Isn't this going to complain if the translation macro debugging is enabled?
Sorry, I don't what is the translation macro. Can you tell me.
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