On Tue, Aug 5, 2025 at 10:18 PM Andrey Ryabinin [off-list ref] wrote:

On 8/5/25 4:26 PM, Sabyrzhan Tasbolatov wrote:

quoted

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 <redacted>
---
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

quoted

      /* 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();
 }