Messages in this thread | | | Subject | Re: [PATCH v2 1/1] riscv/kasan: add KASAN_VMALLOC support | From | Alex Ghiti <> | Date | Sun, 21 Feb 2021 08:38:04 -0500 |
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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@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) {
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