linux-kernel - [PATCH] LoongArch: Disable KASAN if PGDIR_SIZE is too large for cpu

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Message-ID: <20241030081110.3431220-1-chenhuacai@loongson.cn>
Date: Wed, 30 Oct 2024 16:11:10 +0800
From: Huacai Chen <chenhuacai@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>
Cc: loongarch@...ts.linux.dev,
	Xuefeng Li <lixuefeng@...ngson.cn>,
	Guo Ren <guoren@...nel.org>,
	Xuerui Wang <kernel@...0n.name>,
	Jiaxun Yang <jiaxun.yang@...goat.com>,
	linux-kernel@...r.kernel.org,
	loongson-kernel@...ts.loongnix.cn,
	Huacai Chen <chenhuacai@...ngson.cn>
Subject: [PATCH] LoongArch: Disable KASAN if PGDIR_SIZE is too large for cpu_vabits

If PGDIR_SIZE is too large for cpu_vabits, KASAN_SHADOW_END will
overflow UINTPTR_MAX because KASAN_SHADOW_START/KASAN_SHADOW_END are
aligned up by PGDIR_SIZE. And then the overflowed KASAN_SHADOW_END looks
like a user space address.

For example, PGDIR_SIZE of CONFIG_4KB_4LEVEL is 2^39, which is too large
for Loongson-2K series whose cpu_vabits = 39.

Since CONFIG_4KB_4LEVEL is completely legal for CPUs with cpu_vabits <=
39, we just disable KASAN via early return in kasan_init(). Otherwise we
get a boot failure.

Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
---
 arch/loongarch/mm/kasan_init.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/loongarch/mm/kasan_init.c b/arch/loongarch/mm/kasan_init.c
index 4a0d1880dd71..6bdcc8751d4e 100644
--- a/arch/loongarch/mm/kasan_init.c
+++ b/arch/loongarch/mm/kasan_init.c
@@ -262,6 +262,17 @@ void __init kasan_init(void)
 	u64 i;
 	phys_addr_t pa_start, pa_end;
 
+	/*
+	 * If PGDIR_SIZE is too large for cpu_vabits, KASAN_SHADOW_END will
+	 * overflow UINTPTR_MAX and then looks like a user space address.
+	 * For example, PGDIR_SIZE of CONFIG_4KB_4LEVEL is 2^39, which is too
+	 * large for Loongson-2K series whose cpu_vabits = 39.
+	 */
+	if (KASAN_SHADOW_END < vm_map_base) {
+		pr_warn("PGDIR_SIZE too large for cpu_vabits, KernelAddressSanitizer disabled.\n");
+		return;
+	}
+
 	/*
 	 * PGD was populated as invalid_pmd_table or invalid_pud_table
 	 * in pagetable_init() which depends on how many levels of page
-- 
2.43.5