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

[Alex Ghiti <alex@ghiti.fr>]

Hi Nylon, Palmer,

Le 2/8/21 à 1:28 AM, Alex Ghiti a écrit :
> 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

I implemented this morning a version that fixes all the comments I made 
earlier. I was able to insert test_kasan_module on both sv39 and sv48 
without any modification: set_pgd "goes through" all the unused page 
table levels, whereas p*d_populate are noop for unused levels.

If you have any comment, do not hesitate.

diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c 

index adbf94b7e68a..d643b222167c 100644 

--- a/arch/riscv/mm/kasan_init.c 

+++ b/arch/riscv/mm/kasan_init.c 

@@ -195,6 +195,31 @@ static void __init kasan_populate(void *start, void 
*end)
         memset(start, KASAN_SHADOW_INIT, end - start); 

  } 

 

+void __init kasan_shallow_populate_pgd(unsigned long vaddr, unsigned 
long end)
+{ 

+       unsigned long next; 

+       void *p; 

+       pgd_t *pgd_k = pgd_offset_k(vaddr); 

+ 

+       do { 

+               next = pgd_addr_end(vaddr, end); 

+               if (pgd_page_vaddr(*pgd_k) == (unsigned 
long)lm_alias(kasan_early_shadow_pgd_next)) {
+                       p = memblock_alloc(PAGE_SIZE, PAGE_SIZE); 

+                       set_pgd(pgd_k, pfn_pgd(PFN_DOWN(__pa(p)), 
PAGE_TABLE));
+               } 

+       } while (pgd_k++, vaddr = next, vaddr != end); 

+} 

+ 

+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); 

+ 

+       kasan_shallow_populate_pgd(vaddr, vend); 

+ 

+       local_flush_tlb_all(); 

+} 

+ 

  void __init kasan_init(void) 

  { 

         phys_addr_t _start, _end; 

@@ -206,7 +231,15 @@ 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));
 

         /* Populate the linear mapping */ 

         for_each_mem_range(i, &_start, &_end) { 

-- 

2.20.1

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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> 
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