FAILED: Patch "LoongArch: Rework KASAN initialization for PTW-enabled systems" failed to apply to 5.10-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 5ec5ac4ca27e4daa234540ac32f9fc5219377d53 Mon Sep 17 00:00:00 2001
From: Tiezhu Yang <yangtiezhu@loongson.cn>
Date: Tue, 10 Feb 2026 19:31:17 +0800
Subject: [PATCH] LoongArch: Rework KASAN initialization for PTW-enabled
 systems

kasan_init_generic() 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_init_generic()

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_init_generic() later can defer the occasion
of kasan_enabled(), so as to avoid speculative accesses on shadow pages.

After moving kasan_init_generic() 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 | 78 +++++++++++++++++-----------------
 1 file changed, 40 insertions(+), 38 deletions(-)

diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
index 170da98ad4f55..0fc02ca064573 100644
--- a/arch/loongarch/mm/kasan_init.c
+++ b/arch/loongarch/mm/kasan_init.c
@@ -40,39 +40,43 @@ 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)))
 
-void *kasan_mem_to_shadow(const void *addr)
+static void *mem_to_shadow(const void *addr)
 {
-	if (!kasan_enabled()) {
+	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_enabled())
+		return mem_to_shadow(addr);
+	else
+		return (void *)(kasan_early_shadow_page);
 }
 
 const void *kasan_shadow_to_mem(const void *shadow_addr)
@@ -293,11 +297,8 @@ 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));
-
-	/* Enable KASAN here before kasan_mem_to_shadow(). */
-	kasan_init_generic();
+	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) {
@@ -307,13 +308,13 @@ 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.
@@ -328,4 +329,5 @@ void __init kasan_init(void)
 
 	/* At this point kasan is fully initialized. Enable error messages */
 	init_task.kasan_depth = 0;
+	kasan_init_generic();
 }
-- 
2.51.0