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From:   Alex Ghiti <alex@ghiti.fr>
Subject: Re: [PATCH v2 1/1] riscv/kasan: add KASAN_VMALLOC support
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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Message-ID: <2b2f3038-3e27-8763-cf78-3fbbfd2100a0@ghiti.fr>
Date:   Mon, 8 Feb 2021 01:28:13 -0500
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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

>> +??? }
>> +}
>> +
>> ?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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