arm64: kasan: don't populate vmalloc area for CONFIG_KASAN_VMALLOC

Linux support KAsan for VMALLOC since commit 3c5c3cfb
("kasan: support backing vmalloc space with real shadow memory")

Like how the MODULES_VADDR does now, just not to early populate
the VMALLOC_START between VMALLOC_END.

Before:

MODULE_VADDR: no mapping, no zero shadow at init
VMALLOC_VADDR: backed with zero shadow at init

After:

MODULE_VADDR: no mapping, no zero shadow at init
VMALLOC_VADDR: no mapping, no zero shadow at init

Thus the mapping will get allocated on demand by the core function
of KASAN_VMALLOC.

  -----------  vmalloc_shadow_start
 |           |
 |           |
 |           | <= non-mapping
 |           |
 |           |
 |-----------|
 |///////////|<- kimage shadow with page table mapping.
 |-----------|
 |           |
 |           | <= non-mapping
 |           |
 ------------- vmalloc_shadow_end
 |00000000000|
 |00000000000| <= Zero shadow
 |00000000000|
 ------------- KASAN_SHADOW_END
Signed-off-by: NLecopzer Chen <lecopzer.chen@mediatek.com>
Acked-by: NAndrey Konovalov <andreyknvl@gmail.com>
Tested-by: NAndrey Konovalov <andreyknvl@gmail.com>
Tested-by: NArd Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20210324040522.15548-2-lecopzer.chen@mediatek.com
[catalin.marinas@arm.com: add a build check on VMALLOC_START != MODULES_END]
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>

arch/arm64/mm/kasan_init.c

@@ -214,6 +214,7 @@ static void __init kasan_init_shadow(void)
 {
 	u64 kimg_shadow_start, kimg_shadow_end;
 	u64 mod_shadow_start, mod_shadow_end;
+	u64 vmalloc_shadow_end;
 	phys_addr_t pa_start, pa_end;
 	u64 i;
 
@@ -223,6 +224,8 @@ static void __init kasan_init_shadow(void)
 	mod_shadow_start = (u64)kasan_mem_to_shadow((void *)MODULES_VADDR);
 	mod_shadow_end = (u64)kasan_mem_to_shadow((void *)MODULES_END);
 
+	vmalloc_shadow_end = (u64)kasan_mem_to_shadow((void *)VMALLOC_END);
+
 	/*
 	 * We are going to perform proper setup of shadow memory.
 	 * At first we should unmap early shadow (clear_pgds() call below).
@@ -241,12 +244,18 @@ static void __init kasan_init_shadow(void)
 
 	kasan_populate_early_shadow(kasan_mem_to_shadow((void *)PAGE_END),
 				   (void *)mod_shadow_start);
-	kasan_populate_early_shadow((void *)kimg_shadow_end,
-				   (void *)KASAN_SHADOW_END);
 
-	if (kimg_shadow_start > mod_shadow_end)
-		kasan_populate_early_shadow((void *)mod_shadow_end,
-					    (void *)kimg_shadow_start);
+	if (IS_ENABLED(CONFIG_KASAN_VMALLOC)) {
+		BUILD_BUG_ON(VMALLOC_START != MODULES_END);
+		kasan_populate_early_shadow((void *)vmalloc_shadow_end,
+					    (void *)KASAN_SHADOW_END);
+	} else {
+		kasan_populate_early_shadow((void *)kimg_shadow_end,
+					    (void *)KASAN_SHADOW_END);
+		if (kimg_shadow_start > mod_shadow_end)
+			kasan_populate_early_shadow((void *)mod_shadow_end,
+						    (void *)kimg_shadow_start);
+	}
 
 	for_each_mem_range(i, &pa_start, &pa_end) {
 		void *start = (void *)__phys_to_virt(pa_start);