Re: [PATCH v2 1/1] riscv/kasan: add KASAN_VMALLOC support

[Alex Ghiti <alex@ghiti.fr>]

Hi Nylon,

Le 1/22/21 à 10:56 PM, Palmer Dabbelt a écrit :
> On Fri, 15 Jan 2021 21:58:35 PST (-0800), nylon7@andestech.com wrote:
>> It references to x86/s390 architecture.
>> >> So, it doesn't map the early shadow page to cover VMALLOC space.
>>
>> Prepopulate top level page table for the range that would otherwise be
>> empty.
>>
>> lower levels are filled dynamically upon memory allocation while
>> booting.

I think we can improve the changelog a bit here with something like that:

"KASAN vmalloc space used to be mapped using kasan early shadow page. 
KASAN_VMALLOC requires the top-level of the kernel page table to be 
properly populated, lower levels being filled dynamically upon memory 
allocation at runtime."

>>
>> Signed-off-by: Nylon Chen <nylon7@andestech.com>
>> Signed-off-by: Nick Hu <nickhu@andestech.com>
>> ---
>>  arch/riscv/Kconfig         |  1 +
>>  arch/riscv/mm/kasan_init.c | 57 +++++++++++++++++++++++++++++++++++++-
>>  2 files changed, 57 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index 81b76d44725d..15a2c8088bbe 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -57,6 +57,7 @@ config RISCV
>>      select HAVE_ARCH_JUMP_LABEL
>>      select HAVE_ARCH_JUMP_LABEL_RELATIVE
>>      select HAVE_ARCH_KASAN if MMU && 64BIT
>> +    select HAVE_ARCH_KASAN_VMALLOC if MMU && 64BIT
>>      select HAVE_ARCH_KGDB
>>      select HAVE_ARCH_KGDB_QXFER_PKT
>>      select HAVE_ARCH_MMAP_RND_BITS if MMU
>> diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
>> index 12ddd1f6bf70..4b9149f963d3 100644
>> --- a/arch/riscv/mm/kasan_init.c
>> +++ b/arch/riscv/mm/kasan_init.c
>> @@ -9,6 +9,19 @@
>>  #include <linux/pgtable.h>
>>  #include <asm/tlbflush.h>
>>  #include <asm/fixmap.h>
>> +#include <asm/pgalloc.h>
>> +
>> +static __init void *early_alloc(size_t size, int node)
>> +{
>> +    void *ptr = memblock_alloc_try_nid(size, size,
>> +        __pa(MAX_DMA_ADDRESS), MEMBLOCK_ALLOC_ACCESSIBLE, node);
>> +
>> +    if (!ptr)
>> +        panic("%pS: Failed to allocate %zu bytes align=%zx nid=%d 
>> from=%llx\n",
>> +            __func__, size, size, node, (u64)__pa(MAX_DMA_ADDRESS));
>> +
>> +    return ptr;
>> +}
>>
>>  extern pgd_t early_pg_dir[PTRS_PER_PGD];
>>  asmlinkage void __init kasan_early_init(void)
>> @@ -83,6 +96,40 @@ static void __init populate(void *start, void *end)
>>      memset(start, 0, end - start);
>>  }
>>
>> +void __init kasan_shallow_populate(void *start, void *end)
>> +{
>> +    unsigned long vaddr = (unsigned long)start & PAGE_MASK;
>> +    unsigned long vend = PAGE_ALIGN((unsigned long)end);
>> +    unsigned long pfn;
>> +    int index;
>> +    void *p;
>> +    pud_t *pud_dir, *pud_k;
>> +    pgd_t *pgd_dir, *pgd_k;
>> +    p4d_t *p4d_dir, *p4d_k;
>> +
>> +    while (vaddr < vend) {
>> +        index = pgd_index(vaddr);
>> +        pfn = csr_read(CSR_SATP) & SATP_PPN;

At this point in the boot process, we know that we use swapper_pg_dir so 
no need to read SATP.

>> +        pgd_dir = (pgd_t *)pfn_to_virt(pfn) + index;

Here, this pgd_dir assignment is overwritten 2 lines below, so no need 
for it.

>> +        pgd_k = init_mm.pgd + index;
>> +        pgd_dir = pgd_offset_k(vaddr);

pgd_offset_k(vaddr) = init_mm.pgd + pgd_index(vaddr) so pgd_k == pgd_dir.

>> +        set_pgd(pgd_dir, *pgd_k);
>> +
>> +        p4d_dir = p4d_offset(pgd_dir, vaddr);
>> +        p4d_k  = p4d_offset(pgd_k, vaddr);
>> +
>> +        vaddr = (vaddr + PUD_SIZE) & PUD_MASK;

Why do you increase vaddr *before* populating the first one ? And 
pud_addr_end does that properly: it returns the next pud address if it 
does not go beyond end address to map.

>> +        pud_dir = pud_offset(p4d_dir, vaddr);
>> +        pud_k = pud_offset(p4d_k, vaddr);
>> +
>> +        if (pud_present(*pud_dir)) {
>> +            p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
>> +            pud_populate(&init_mm, pud_dir, p);

init_mm is not needed here.

>> +        }
>> +        vaddr += PAGE_SIZE;

Why do you need to add PAGE_SIZE ? vaddr already points to the next pud.

It seems like this patch tries to populate userspace page table whereas 
at this point in the boot process, only swapper_pg_dir is used or am I 
missing something ?

Thanks,

Alex

>> +    }
>> +}
>> +
>>  void __init kasan_init(void)
>>  {
>>      phys_addr_t _start, _end;
>> @@ -90,7 +137,15 @@ void __init kasan_init(void)
>>
>>      kasan_populate_early_shadow((void *)KASAN_SHADOW_START,
>>                      (void *)kasan_mem_to_shadow((void *)
>> -                                VMALLOC_END));
>> +                                VMEMMAP_END));
>> +    if (IS_ENABLED(CONFIG_KASAN_VMALLOC))
>> +        kasan_shallow_populate(
>> +            (void *)kasan_mem_to_shadow((void *)VMALLOC_START),
>> +            (void *)kasan_mem_to_shadow((void *)VMALLOC_END));
>> +    else
>> +        kasan_populate_early_shadow(
>> +            (void *)kasan_mem_to_shadow((void *)VMALLOC_START),
>> +            (void *)kasan_mem_to_shadow((void *)VMALLOC_END));
>>
>>      for_each_mem_range(i, &_start, &_end) {
>>          void *start = (void *)_start; >
> Thanks, this is on for-next.
> 
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