Message-ID: <af58ed3d-36e4-1278-dc42-7df2d875abbc@ghiti.fr>
Date:   Mon, 22 Feb 2021 12:13:05 -0500
From:   Alex Ghiti <alex@...ti.fr>
To:     Nylon Chen <nylon7@...estech.com>
Cc:     "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        Nick Chun-Ming Hu(胡峻銘) 
        <nickhu@...estech.com>,
        Alan Quey-Liang Kao(高魁良) 
        <alankao@...estech.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        "nylon7717@...il.com" <nylon7717@...il.com>,
        "aryabinin@...tuozzo.com" <aryabinin@...tuozzo.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        "glider@...gle.com" <glider@...gle.com>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>
Subject: Re: [PATCH v2 1/1] riscv/kasan: add KASAN_VMALLOC support

Le 2/21/21 à 8:37 PM, Nylon Chen a écrit :
> Hi Alex, Palmer
> 
> Sorry I missed this message.
> On Sun, Feb 21, 2021 at 09:38:04PM +0800, Alex Ghiti wrote:
>> Le 2/13/21 à 5:52 AM, Alex Ghiti a écrit :
>>> 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@...estech.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@...estech.com>
>>>>>> Signed-off-by: Nick Hu <nickhu@...estech.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);
>>> +}
>>> +
>>
>> This way of going through the page table seems to be largely used across
>> the kernel (cf KASAN population functions of arm64/x86) so I do think
>> this patch brings value to Nylon and Nick's patch.
>>
>> I can propose a real patch if you agree and I'll add a co-developed by
>> Nylon/Nick since this only 'improves' theirs.
>>
>> Thanks,
>>
>> Alex
>>
> I agree with your proposal, but when I try your patch that it dosen't work
> because `kasan_early_shadow_pgd_next` function wasn't define.

Oops, I messed up my rebase, please replace 
'kasan_early_shadow_pgd_next' with 'kasan_early_shadow_pmd'.

Thank you for your feeback,

Alex

> 
> Do you have complete patch? or just I missed some content?
>>> +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) {
> 
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