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

[Nylon Chen]

Hi Alex, Palmer
On Thu, Feb 25, 2021 at 03:11:07AM +0800, Alex Ghiti wrote:
> Hi Nylon,
> 
> Le 2/22/21 ?? 12:13 PM, Alex Ghiti a ??crit??:
> > Le 2/21/21 ?? 8:37 PM, Nylon Chen a ??crit??:
> >> 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 ?? 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@xxxxxxxxxxxxx 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@xxxxxxxxxxxxx>
> >>>>>>> Signed-off-by: Nick Hu <nickhu@xxxxxxxxxxxxx>
> >>>>>>> ---
> >>>>>>> ????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
> > 
> 
> Did you have time to test the above fix ? It would be nice to replace 
> your current patch with the above solution before it gets merged for 
> 5.12, I will propose something tomorrow, feel free to review and test :)
> 
> Thanks again,
> 
> Alex
> 
Today I follow your fix in our platform, it's workable.

Thank you for your fix.
> >>
> >> 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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> >>