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Subject: Re: [PATCH v2 1/1] riscv/kasan: add KASAN_VMALLOC support
From:   Alex Ghiti <alex@ghiti.fr>
To:     Palmer Dabbelt <palmer@dabbelt.com>, nylon7@andestech.com
Cc:     aou@eecs.berkeley.edu, nickhu@andestech.com, alankao@andestech.com,
        linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
        nylon7717@gmail.com, glider@google.com,
        Paul Walmsley <paul.walmsley@sifive.com>,
        aryabinin@virtuozzo.com, linux-riscv@lists.infradead.org,
        dvyukov@google.com
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Date:   Sun, 21 Feb 2021 08:38:04 -0500
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Le 2/13/21 ? 5:52 AM, Alex Ghiti a ?crit?:
> Hi Nylon, Palmer,
> 
> Le 2/8/21 ? 1:28 AM, Alex Ghiti a ?crit?:
>> Hi Nylon,
>>
>> Le 1/22/21 ? 10:56 PM, Palmer Dabbelt a ?crit?:
>>> 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);
> +}
> +

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

> +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) {