Re: [PATCH v2] riscv: Improve KASAN_VMALLOC support

[Alex Ghiti]

Le 3/9/21 à 9:37 PM, Palmer Dabbelt a écrit :
> On Fri, 26 Feb 2021 10:01:54 PST (-0800), alex@xxxxxxxx wrote:
> > When KASAN vmalloc region is populated, there is no userspace process and
> > the page table in use is swapper_pg_dir, so there is no need to read
> > SATP. Then we can use the same scheme used by kasan_populate_p*d
> > functions to go through the page table, which harmonizes the code.
> >
> > In addition, make use of set_pgd that goes through all unused page table
> > levels, contrary to p*d_populate functions, which makes this function 
> > work
> > whatever the number of page table levels.
> >
> > And finally, make sure the writes to swapper_pg_dir are visible using
> > an sfence.vma.
>
> So I think this is actually a bug: without the fence we could get a 
> kasan-related fault at any point (as the mappings might not be visible 
> yet), and if we get one when inside do_page_fault() (or while holding a 
> lock it wants) we'll end up deadlocking against ourselves.  That'll 
> probably never happen in practice, but it'd still be good to get the 
> fence onto fixes. The rest are cleanups, they're for for-next (and 
> should probably be part of your sv48 series, if you need to re-spin it 
> -- I'll look at that next).

I only talked about sv48 support in the changelog as it explains why I 
replaced p*d_populate functions for set_p*d, this is not directly linked 
to the sv48 patchset, this is just a bonus that it works for both :)

> LMK if you want to split this up, or if you want me to do it.  Either way,

I'll split it up: one patch for the cleanup and one patch for the fix.

> Reviewed-by: Palmer Dabbelt <palmerdabbelt@xxxxxxxxxx>

Thanks,

Alex

> Thanks!
>
> > Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> > ---
> >
> > Changes in v2:
> > - Quiet kernel test robot warnings about missing prototypes by declaring
> >   the introduced functions as static.
> >
> >  arch/riscv/mm/kasan_init.c | 61 +++++++++++++-------------------------
> >  1 file changed, 20 insertions(+), 41 deletions(-)
> >
> > diff --git a/arch/riscv/mm/kasan_init.c b/arch/riscv/mm/kasan_init.c
> > index e3d91f334b57..aaa3bdc0ffc0 100644
> > --- a/arch/riscv/mm/kasan_init.c
> > +++ b/arch/riscv/mm/kasan_init.c
> > @@ -11,18 +11,6 @@
> >  #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)
> >  {
> > @@ -155,38 +143,29 @@ static void __init kasan_populate(void *start, 
> > void *end)
> >      memset(start, KASAN_SHADOW_INIT, end - start);
> >  }
> >
> > -void __init kasan_shallow_populate(void *start, void *end)
> > +static void __init kasan_shallow_populate_pgd(unsigned long vaddr, 
> > unsigned long end)
> >  {
> > -    unsigned long vaddr = (unsigned long)start & PAGE_MASK;
> > -    unsigned long vend = PAGE_ALIGN((unsigned long)end);
> > -    unsigned long pfn;
> > -    int index;
> > +    unsigned long next;
> >      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;
> > -        pgd_dir = (pgd_t *)pfn_to_virt(pfn) + index;
> > -        pgd_k = init_mm.pgd + index;
> > -        pgd_dir = pgd_offset_k(vaddr);
> > -        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;
> > -        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);
> > +    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_pmd)) {
> > +            p = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +            set_pgd(pgd_k, pfn_pgd(PFN_DOWN(__pa(p)), PAGE_TABLE));
> >          }
> > -        vaddr += PAGE_SIZE;
> > -    }
> > +    } while (pgd_k++, vaddr = next, vaddr != end);
> > +}
> > +
> > +static 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)
>
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