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* [PATCH for 6.6 & 6.12] LoongArch: Rework KASAN initialization for PTW-enabled systems
@ 2026-02-15 14:09 Huacai Chen
  2026-02-16  9:52 ` Greg Kroah-Hartman
  0 siblings, 1 reply; 5+ messages in thread
From: Huacai Chen @ 2026-02-15 14:09 UTC (permalink / raw)
  To: Greg Kroah-Hartman, Sasha Levin, Huacai Chen
  Cc: Xuerui Wang, stable, linux-kernel, loongarch, Tiezhu Yang,
	Huacai Chen

From: Tiezhu Yang <yangtiezhu@loongson.cn>

commit 5ec5ac4ca27e4daa234540ac32f9fc5219377d53 upstream.

"kasan_early_stage = false" indicates that kasan is fully initialized,
so it should be put at end of kasan_init().

Otherwise bringing up the primary CPU failed when CONFIG_KASAN is set
on PTW-enabled systems, here are the call chains:

    kernel_entry()
      start_kernel()
        setup_arch()
          kasan_init()
            kasan_early_stage = false

The reason is PTW-enabled systems have speculative accesses which means
memory accesses to the shadow memory after kasan_init() may be executed
by hardware before. However, accessing shadow memory is safe only after
kasan fully initialized because kasan_init() uses a temporary PGD table
until we have populated all levels of shadow page tables and writen the
PGD register. Moving "kasan_early_stage = false" later can defer the
occasion of kasan_arch_is_ready(), so as to avoid speculative accesses
on shadow pages.

After moving "kasan_early_stage = false" to the end, kasan_init() can no
longer call kasan_mem_to_shadow() for shadow address conversion because
it will always return kasan_early_shadow_page. On the other hand, we
should keep the current logic of kasan_mem_to_shadow() for both the early
and final stage because there may be instrumentation before kasan_init().

To solve this, we factor out a new mem_to_shadow() function from current
kasan_mem_to_shadow() for the shadow address conversion in kasan_init().

Cc: stable@vger.kernel.org
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
---
 arch/loongarch/mm/kasan_init.c | 77 ++++++++++++++++++----------------
 1 file changed, 40 insertions(+), 37 deletions(-)

diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
index d2681272d8f0..9337380a70eb 100644
--- a/arch/loongarch/mm/kasan_init.c
+++ b/arch/loongarch/mm/kasan_init.c
@@ -42,39 +42,43 @@ static pgd_t kasan_pg_dir[PTRS_PER_PGD] __initdata __aligned(PAGE_SIZE);
 
 bool kasan_early_stage = true;
 
-void *kasan_mem_to_shadow(const void *addr)
+static void *mem_to_shadow(const void *addr)
 {
-	if (!kasan_arch_is_ready()) {
+	unsigned long offset = 0;
+	unsigned long maddr = (unsigned long)addr;
+	unsigned long xrange = (maddr >> XRANGE_SHIFT) & 0xffff;
+
+	if (maddr >= FIXADDR_START)
 		return (void *)(kasan_early_shadow_page);
-	} else {
-		unsigned long maddr = (unsigned long)addr;
-		unsigned long xrange = (maddr >> XRANGE_SHIFT) & 0xffff;
-		unsigned long offset = 0;
-
-		if (maddr >= FIXADDR_START)
-			return (void *)(kasan_early_shadow_page);
-
-		maddr &= XRANGE_SHADOW_MASK;
-		switch (xrange) {
-		case XKPRANGE_CC_SEG:
-			offset = XKPRANGE_CC_SHADOW_OFFSET;
-			break;
-		case XKPRANGE_UC_SEG:
-			offset = XKPRANGE_UC_SHADOW_OFFSET;
-			break;
-		case XKPRANGE_WC_SEG:
-			offset = XKPRANGE_WC_SHADOW_OFFSET;
-			break;
-		case XKVRANGE_VC_SEG:
-			offset = XKVRANGE_VC_SHADOW_OFFSET;
-			break;
-		default:
-			WARN_ON(1);
-			return NULL;
-		}
 
-		return (void *)((maddr >> KASAN_SHADOW_SCALE_SHIFT) + offset);
+	maddr &= XRANGE_SHADOW_MASK;
+	switch (xrange) {
+	case XKPRANGE_CC_SEG:
+		offset = XKPRANGE_CC_SHADOW_OFFSET;
+		break;
+	case XKPRANGE_UC_SEG:
+		offset = XKPRANGE_UC_SHADOW_OFFSET;
+		break;
+	case XKPRANGE_WC_SEG:
+		offset = XKPRANGE_WC_SHADOW_OFFSET;
+		break;
+	case XKVRANGE_VC_SEG:
+		offset = XKVRANGE_VC_SHADOW_OFFSET;
+		break;
+	default:
+		WARN_ON(1);
+		return NULL;
 	}
+
+	return (void *)((maddr >> KASAN_SHADOW_SCALE_SHIFT) + offset);
+}
+
+void *kasan_mem_to_shadow(const void *addr)
+{
+	if (kasan_arch_is_ready())
+		return mem_to_shadow(addr);
+	else
+		return (void *)(kasan_early_shadow_page);
 }
 
 const void *kasan_shadow_to_mem(const void *shadow_addr)
@@ -295,10 +299,8 @@ void __init kasan_init(void)
 	/* Maps everything to a single page of zeroes */
 	kasan_pgd_populate(KASAN_SHADOW_START, KASAN_SHADOW_END, NUMA_NO_NODE, true);
 
-	kasan_populate_early_shadow(kasan_mem_to_shadow((void *)VMALLOC_START),
-					kasan_mem_to_shadow((void *)KFENCE_AREA_END));
-
-	kasan_early_stage = false;
+	kasan_populate_early_shadow(mem_to_shadow((void *)VMALLOC_START),
+					mem_to_shadow((void *)KFENCE_AREA_END));
 
 	/* Populate the linear mapping */
 	for_each_mem_range(i, &pa_start, &pa_end) {
@@ -308,13 +310,13 @@ void __init kasan_init(void)
 		if (start >= end)
 			break;
 
-		kasan_map_populate((unsigned long)kasan_mem_to_shadow(start),
-			(unsigned long)kasan_mem_to_shadow(end), NUMA_NO_NODE);
+		kasan_map_populate((unsigned long)mem_to_shadow(start),
+			(unsigned long)mem_to_shadow(end), NUMA_NO_NODE);
 	}
 
 	/* Populate modules mapping */
-	kasan_map_populate((unsigned long)kasan_mem_to_shadow((void *)MODULES_VADDR),
-		(unsigned long)kasan_mem_to_shadow((void *)MODULES_END), NUMA_NO_NODE);
+	kasan_map_populate((unsigned long)mem_to_shadow((void *)MODULES_VADDR),
+		(unsigned long)mem_to_shadow((void *)MODULES_END), NUMA_NO_NODE);
 	/*
 	 * KAsan may reuse the contents of kasan_early_shadow_pte directly, so we
 	 * should make sure that it maps the zero page read-only.
@@ -329,5 +331,6 @@ void __init kasan_init(void)
 
 	/* At this point kasan is fully initialized. Enable error messages */
 	init_task.kasan_depth = 0;
+	kasan_early_stage = false;
 	pr_info("KernelAddressSanitizer initialized.\n");
 }
-- 
2.52.0


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2026-02-15 14:09 [PATCH for 6.6 & 6.12] LoongArch: Rework KASAN initialization for PTW-enabled systems Huacai Chen
2026-02-16  9:52 ` Greg Kroah-Hartman
2026-02-16 10:09   ` Huacai Chen
2026-02-16 10:20     ` Greg Kroah-Hartman
2026-02-16 10:34       ` Huacai Chen

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