Re: [PATCH] LoongArch: Add kernel address sanitizer support

[Qing Zhang]

Hi, Andrey
On 2023/3/30 上午3:02, Andrey Konovalov wrote:
> > diff --git a/include/linux/kasan.h b/include/linux/kasan.h
> > index f7ef70661ce2..3b91b941873d 100644
> > --- a/include/linux/kasan.h
> > +++ b/include/linux/kasan.h
> > @@ -54,11 +54,13 @@ extern p4d_t kasan_early_shadow_p4d[MAX_PTRS_PER_P4D];
> >   int kasan_populate_early_shadow(const void *shadow_start,
> >                                  const void *shadow_end);
> >
> > +#ifndef __HAVE_ARCH_SHADOW_MAP
> >   static inline void *kasan_mem_to_shadow(const void *addr)
> >   {
> >          return (void *)((unsigned long)addr >> KASAN_SHADOW_SCALE_SHIFT)
> >                  + KASAN_SHADOW_OFFSET;
> >   }
> > +#endif
> >
> >   int kasan_add_zero_shadow(void *start, unsigned long size);
> >   void kasan_remove_zero_shadow(void *start, unsigned long size);
> > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> > index e5eef670735e..f86194750df5 100644
> > --- a/mm/kasan/generic.c
> > +++ b/mm/kasan/generic.c
> > @@ -175,6 +175,11 @@ static __always_inline bool check_region_inline(unsigned long addr,
> >          if (unlikely(!addr_has_metadata((void *)addr)))
> >                  return !kasan_report(addr, size, write, ret_ip);
> >
> > +#ifndef __HAVE_ARCH_SHADOW_MAP
> > +       if (unlikely(kasan_mem_to_shadow((unsigned long *)addr) == NULL))
> > +               return !kasan_report(addr, size, write, ret_ip);
> > +#endif
>
> This should have been ifdef, right?
Sorry, it was a clerical error,
Here it is
#ifndef __HAVE_ARCH_SHADOW_MAP
if (unlikely(! addr_has_metadata((void *)addr)))
return ! kasan_report(addr, size, write, ret_ip);
#else
if (unlikely(kasan_mem_to_shadow((void *)addr) == NULL)) {
kasan_report(addr, size, write, ret_ip);
return;
}
#endif
> But I don't think you need this check here at all: addr_has_metadata
> already checks that shadow exists.
On LongArch, there's a lot of holes between different segments, so kasan
shadow area is some different type of memory that we concatenate, we
can't use if (unlikely((void *)addr <
kasan_shadow_to_mem((void *)KASAN_SHADOW_START))) to determine the
validity, and in arch/loongarch/include/asm/kasan.h I construct invalid
NULL.
> > +
> >          if (likely(!memory_is_poisoned(addr, size)))
> >                  return true;
> >
> > diff --git a/mm/kasan/init.c b/mm/kasan/init.c
> > index cc64ed6858c6..860061a22ca9 100644
> > --- a/mm/kasan/init.c
> > +++ b/mm/kasan/init.c
> > @@ -166,8 +166,9 @@ static int __ref zero_pud_populate(p4d_t *p4d, unsigned long addr,
> >                                  if (!p)
> >                                          return -ENOMEM;
> >                          } else {
> > -                               pud_populate(&init_mm, pud,
> > -                                       early_alloc(PAGE_SIZE, NUMA_NO_NODE));
> > +                               p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
> > +                               pmd_init(p);
> > +                               pud_populate(&init_mm, pud, p);
> >                          }
> >                  }
> >                  zero_pmd_populate(pud, addr, next);
> > @@ -207,8 +208,9 @@ static int __ref zero_p4d_populate(pgd_t *pgd, unsigned long addr,
> >                                  if (!p)
> >                                          return -ENOMEM;
> >                          } else {
> > -                               p4d_populate(&init_mm, p4d,
> > -                                       early_alloc(PAGE_SIZE, NUMA_NO_NODE));
> > +                               p = early_alloc(PAGE_SIZE, NUMA_NO_NODE);
> > +                               pud_init(p);
> > +                               p4d_populate(&init_mm, p4d, p);
>
> Please explain why these changes are needed in the patch description.

This is because in pagetable_init on loongarch/mips, we populate pmd/pud
with invalid_pmd_table/invalid_pud_table,
So pmd_init/pud_init(p) is required, perhaps we define them as __weak in
mm/kasan/init.c, like mm/sparse-vmemmap.c.

diff --git a/include/linux/mm.h  b/include/linux/mm.h
...
+void pmd_init(void *addr);
+void pud_init(void *addr);
...
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
...
+void __weak __meminit pmd_init(void *addr)
+ {
+}
+
@@-203,11 +207,16 @@pud_t * __meminit vmemmap_pud_populate(p4d_t *p4d, 
unsigned long addr, int node)
void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
if (! p)
return NULL;
+               pmd_init(p);
pud_populate(&init_mm, pud, p);
}
return pud;
}
+void __weak __meminit pud_init(void *addr)
+ {
+}
+
p4d_t * __meminit vmemmap_p4d_populate(pgd_t *pgd, unsigned long addr, 
int node)
{
p4d_t *p4d = p4d_offset(pgd, addr);
@@-215,6 +224,7 @@p4d_t * __meminit vmemmap_p4d_populate(pgd_t *pgd, 
unsigned long addr, int node)
void *p = vmemmap_alloc_block_zero(PAGE_SIZE, node);
if (! p)
return NULL;
+               pud_init(p);
p4d_populate(&init_mm, p4d, p);
}
return p4d;

Thanks,
- Qing
> >                          }
> >                  }
> >                  zero_pud_populate(p4d, addr, next);
> > diff --git a/mm/kasan/kasan.h b/mm/kasan/kasan.h
> > index a61eeee3095a..033335c13b25 100644
> > --- a/mm/kasan/kasan.h
> > +++ b/mm/kasan/kasan.h
> > @@ -291,16 +291,22 @@ struct kasan_stack_ring {
> >
> >   #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
> >
> > +#ifndef __HAVE_ARCH_SHADOW_MAP
> >   static inline const void *kasan_shadow_to_mem(const void *shadow_addr)
> >   {
> >          return (void *)(((unsigned long)shadow_addr - KASAN_SHADOW_OFFSET)
> >                  << KASAN_SHADOW_SCALE_SHIFT);
> >   }
> > +#endif
> >
> >   static __always_inline bool addr_has_metadata(const void *addr)
> >   {
> > +#ifdef __HAVE_ARCH_SHADOW_MAP
> > +       return (kasan_mem_to_shadow((void *)addr) != NULL);
> > +#else
> >          return (kasan_reset_tag(addr) >=
> >                  kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
> > +#endif
> >   }
> >
> >   /**
> > --
> > 2.20.1