[PATCH v2 2/2] kasan: Unpoison vms[area] addresses with a common tag

[Maciej Wieczor-Retman <m.wieczorretman@pm.me>]

From: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>

A KASAN tag mismatch, possibly causing a kernel panic, can be observed
on systems with a tag-based KASAN enabled and with multiple NUMA nodes.
It was reported on arm64 and reproduced on x86. It can be explained in
the following points:

	1. There can be more than one virtual memory chunk.
	2. Chunk's base address has a tag.
	3. The base address points at the first chunk and thus inherits
	   the tag of the first chunk.
	4. The subsequent chunks will be accessed with the tag from the
	   first chunk.
	5. Thus, the subsequent chunks need to have their tag set to
	   match that of the first chunk.

Use the modified __kasan_unpoison_vmalloc() to pass the tag of the first
vm_struct's address when vm_structs are unpoisoned in
pcpu_get_vm_areas(). Assigning a common tag resolves the pcpu chunk
address mismatch.

Fixes: 1d96320f8d53 ("kasan, vmalloc: add vmalloc tagging for SW_TAGS")
Cc: <stable@vger.kernel.org> # 6.1+
Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
---
Changelog v2:
- Revise the whole patch to match the fixed refactorization from the
  first patch.

Changelog v1:
- Rewrite the patch message to point at the user impact of the issue.
- Move helper to common.c so it can be compiled in all KASAN modes.

 mm/kasan/common.c  |  3 ++-
 mm/kasan/hw_tags.c | 12 ++++++++----
 mm/kasan/shadow.c  | 15 +++++++++++----
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/mm/kasan/common.c b/mm/kasan/common.c
index 7884ea7d13f9..e5a867a5670b 100644
--- a/mm/kasan/common.c
+++ b/mm/kasan/common.c
@@ -591,11 +591,12 @@ void kasan_unpoison_vmap_areas(struct vm_struct **vms, int nr_vms,
 	unsigned long size;
 	void *addr;
 	int area;
+	u8 tag = get_tag(vms[0]->addr);
 
 	for (area = 0 ; area < nr_vms ; area++) {
 		size = vms[area]->size;
 		addr = vms[area]->addr;
-		vms[area]->addr = __kasan_unpoison_vmap_areas(addr, size, flags);
+		vms[area]->addr = __kasan_unpoison_vmap_areas(addr, size, flags, tag);
 	}
 }
 #endif
diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index 4b7936a2bd6f..2a02b898b9d8 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -317,7 +317,7 @@ static void init_vmalloc_pages(const void *start, unsigned long size)
 }
 
 static void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
-				      kasan_vmalloc_flags_t flags)
+				      kasan_vmalloc_flags_t flags, int unpoison_tag)
 {
 	u8 tag;
 	unsigned long redzone_start, redzone_size;
@@ -361,7 +361,11 @@ static void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
 		return (void *)start;
 	}
 
-	tag = kasan_random_tag();
+	if (unpoison_tag < 0)
+		tag = kasan_random_tag();
+	else
+		tag = unpoison_tag;
+
 	start = set_tag(start, tag);
 
 	/* Unpoison and initialize memory up to size. */
@@ -390,7 +394,7 @@ static void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
 void *__kasan_random_unpoison_vmalloc(const void *start, unsigned long size,
 				      kasan_vmalloc_flags_t flags)
 {
-	return __kasan_unpoison_vmalloc(start, size, flags);
+	return __kasan_unpoison_vmalloc(start, size, flags, -1);
 }
 
 void __kasan_poison_vmalloc(const void *start, unsigned long size)
@@ -405,7 +409,7 @@ void __kasan_poison_vmalloc(const void *start, unsigned long size)
 void *__kasan_unpoison_vmap_areas(void *addr, unsigned long size,
 				  kasan_vmalloc_flags_t flags, u8 tag)
 {
-	return __kasan_unpoison_vmalloc(addr, size, flags);
+	return __kasan_unpoison_vmalloc(addr, size, flags, tag);
 }
 #endif
 
diff --git a/mm/kasan/shadow.c b/mm/kasan/shadow.c
index 0a8d8bf6e9cf..7a66ffc1d5b3 100644
--- a/mm/kasan/shadow.c
+++ b/mm/kasan/shadow.c
@@ -625,8 +625,10 @@ void kasan_release_vmalloc(unsigned long start, unsigned long end,
 }
 
 static void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
-				      kasan_vmalloc_flags_t flags)
+				      kasan_vmalloc_flags_t flags, int unpoison_tag)
 {
+	u8 tag;
+
 	/*
 	 * Software KASAN modes unpoison both VM_ALLOC and non-VM_ALLOC
 	 * mappings, so the KASAN_VMALLOC_VM_ALLOC flag is ignored.
@@ -648,7 +650,12 @@ static void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
 	    !(flags & KASAN_VMALLOC_PROT_NORMAL))
 		return (void *)start;
 
-	start = set_tag(start, kasan_random_tag());
+	if (unpoison_tag < 0)
+		tag = kasan_random_tag();
+	else
+		tag = unpoison_tag;
+
+	start = set_tag(start, tag);
 	kasan_unpoison(start, size, false);
 	return (void *)start;
 }
@@ -656,13 +663,13 @@ static void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
 void *__kasan_random_unpoison_vmalloc(const void *start, unsigned long size,
 				      kasan_vmalloc_flags_t flags)
 {
-	return __kasan_unpoison_vmalloc(start, size, flags);
+	return __kasan_unpoison_vmalloc(start, size, flags, -1);
 }
 
 void *__kasan_unpoison_vmap_areas(void *addr, unsigned long size,
 				  kasan_vmalloc_flags_t flags, u8 tag)
 {
-	return __kasan_unpoison_vmalloc(addr, size, flags);
+	return __kasan_unpoison_vmalloc(addr, size, flags, tag);
 }
 
 /*
-- 
2.52.0