Re: [PATCH v4 5/9] kasan/loongarch: select ARCH_DEFER_KASAN and call kasan_init_generic

[Sabyrzhan Tasbolatov <snovitoll@gmail.com>]

On Tue, Aug 5, 2025 at 10:18 PM Andrey Ryabinin <ryabinin.a.a@gmail.com> wrote:
>
>
>
> On 8/5/25 4:26 PM, Sabyrzhan Tasbolatov wrote:
> > LoongArch needs deferred KASAN initialization as it has a custom
> > kasan_arch_is_ready() implementation that tracks shadow memory
> > readiness via the kasan_early_stage flag.
> >
> > Select ARCH_DEFER_KASAN to enable the unified static key mechanism
> > for runtime KASAN control. Call kasan_init_generic() which handles
> > Generic KASAN initialization and enables the static key.
> >
> > Replace kasan_arch_is_ready() with kasan_enabled() and delete the
> > flag kasan_early_stage in favor of the unified kasan_enabled()
> > interface.
> >
> > Note that init_task.kasan_depth = 0 is called after kasan_init_generic(),
> > which is different than in other arch kasan_init(). This is left
> > unchanged as it cannot be tested.
> >
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217049
> > Signed-off-by: Sabyrzhan Tasbolatov <snovitoll@gmail.com>
> > ---
> > Changes in v4:
> > - Replaced !kasan_enabled() with !kasan_shadow_initialized() in
> >   loongarch which selects ARCH_DEFER_KASAN (Andrey Ryabinin)
> > ---
> >  arch/loongarch/Kconfig             | 1 +
> >  arch/loongarch/include/asm/kasan.h | 7 -------
> >  arch/loongarch/mm/kasan_init.c     | 8 ++------
> >  3 files changed, 3 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> > index f0abc38c40a..f6304c073ec 100644
> > --- a/arch/loongarch/Kconfig
> > +++ b/arch/loongarch/Kconfig
> > @@ -9,6 +9,7 @@ config LOONGARCH
> >       select ACPI_PPTT if ACPI
> >       select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
> >       select ARCH_BINFMT_ELF_STATE
> > +     select ARCH_DEFER_KASAN
> >       select ARCH_DISABLE_KASAN_INLINE
> >       select ARCH_ENABLE_MEMORY_HOTPLUG
> >       select ARCH_ENABLE_MEMORY_HOTREMOVE
> > diff --git a/arch/loongarch/include/asm/kasan.h b/arch/loongarch/include/asm/kasan.h
> > index 62f139a9c87..0e50e5b5e05 100644
> > --- a/arch/loongarch/include/asm/kasan.h
> > +++ b/arch/loongarch/include/asm/kasan.h
> > @@ -66,7 +66,6 @@
> >  #define XKPRANGE_WC_SHADOW_OFFSET    (KASAN_SHADOW_START + XKPRANGE_WC_KASAN_OFFSET)
> >  #define XKVRANGE_VC_SHADOW_OFFSET    (KASAN_SHADOW_START + XKVRANGE_VC_KASAN_OFFSET)
> >
> > -extern bool kasan_early_stage;
> >  extern unsigned char kasan_early_shadow_page[PAGE_SIZE];
> >
> >  #define kasan_mem_to_shadow kasan_mem_to_shadow
> > @@ -75,12 +74,6 @@ void *kasan_mem_to_shadow(const void *addr);
> >  #define kasan_shadow_to_mem kasan_shadow_to_mem
> >  const void *kasan_shadow_to_mem(const void *shadow_addr);
> >
> > -#define kasan_arch_is_ready kasan_arch_is_ready
> > -static __always_inline bool kasan_arch_is_ready(void)
> > -{
> > -     return !kasan_early_stage;
> > -}
> > -
> >  #define addr_has_metadata addr_has_metadata
> >  static __always_inline bool addr_has_metadata(const void *addr)
> >  {
> > diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
> > index d2681272d8f..57fb6e98376 100644
> > --- a/arch/loongarch/mm/kasan_init.c
> > +++ b/arch/loongarch/mm/kasan_init.c
> > @@ -40,11 +40,9 @@ static pgd_t kasan_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
> >  #define __pte_none(early, pte) (early ? pte_none(pte) : \
> >  ((pte_val(pte) & _PFN_MASK) == (unsigned long)__pa(kasan_early_shadow_page)))
> >
> > -bool kasan_early_stage = true;
> > -
> >  void *kasan_mem_to_shadow(const void *addr)
> >  {
> > -     if (!kasan_arch_is_ready()) {
> > +     if (!kasan_shadow_initialized()) {
> >               return (void *)(kasan_early_shadow_page);
> >       } else {
> >               unsigned long maddr = (unsigned long)addr;
> > @@ -298,8 +296,6 @@ void __init kasan_init(void)
> >       kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
> >                                       kasan_mem_to_shadow((void *)KFENCE_AREA_END));
> >
> > -     kasan_early_stage = false;
> > -
>
> There is a reason for this line to be here.
> Your patch will change the result of the follow up kasan_mem_to_shadow() call and
> feed the wrong address to kasan_map_populate()

Thanks, I've missed it. Here the upcoming v5 for this:

diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
index d2681272d8f..0e6622b57ce 100644
--- a/arch/loongarch/mm/kasan_init.c
+++ b/arch/loongarch/mm/kasan_init.c
@@ -40,11 +40,9 @@ static pgd_t kasan_pg_dir[PTRS_PER_PGD] __initdata
__aligned(PAGE_SIZE);
#define __pte_none(early, pte) (early ? pte_none(pte) : \
((pte_val(pte) & _PFN_MASK) == (unsigned long)__pa(kasan_early_shadow_page)))
-bool kasan_early_stage = true;
-
void *kasan_mem_to_shadow(const void *addr)
{
- if (!kasan_arch_is_ready()) {
+ if (!kasan_shadow_initialized()) {
return (void *)(kasan_early_shadow_page);
} else {
unsigned long maddr = (unsigned long)addr;
@@ -298,7 +296,10 @@ void __init kasan_init(void)
kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
kasan_mem_to_shadow((void *)KFENCE_AREA_END));
- kasan_early_stage = false;
+ /* Enable KASAN here before kasan_mem_to_shadow() which checks
+ * if kasan_shadow_initialized().
+ */
+ kasan_init_generic();
/* Populate the linear mapping */
for_each_mem_range(i, &pa_start, &pa_end) {
@@ -329,5 +330,4 @@ void __init kasan_init(void)
/* At this point kasan is fully initialized. Enable error messages */
init_task.kasan_depth = 0;
- pr_info("KernelAddressSanitizer initialized.\n");
}
-- 
2.34.1

>
>
> >       /* Populate the linear mapping */
> >       for_each_mem_range(i, &pa_start, &pa_end) {
> >               void *start = (void *)phys_to_virt(pa_start);
> > @@ -329,5 +325,5 @@ void __init kasan_init(void)
> >
> >       /* At this point kasan is fully initialized. Enable error messages */
> >       init_task.kasan_depth = 0;
> > -     pr_info("KernelAddressSanitizer initialized.\n");
> > +     kasan_init_generic();
> >  }
>