[PATCH] kasan: hw_tags: avoid invalid virt_to_page()

[Mark Rutland]

When booting with 'kasan.vmalloc=off', a kernel configured with support
for KASAN_HW_TAGS will explode at boot time due to bogus use of
virt_to_page() on a vmalloc adddress. With CONFIG_DEBUG_VIRTUAL selected
this will be reported explicitly, and with or without
CONFIG_DEBUG_VIRTUAL the kernel will dereference a bogus address:

| ------------[ cut here ]------------
| virt_to_phys used for non-linear address: (____ptrval____) (0xffff800008000000)
| WARNING: CPU: 0 PID: 0 at arch/arm64/mm/physaddr.c:15 __virt_to_phys+0x78/0x80
| Modules linked in:
| CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.3.0-rc3-00073-g83865133300d-dirty #4
| Hardware name: linux,dummy-virt (DT)
| pstate: 600000c5 (nZCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : __virt_to_phys+0x78/0x80
| lr : __virt_to_phys+0x78/0x80
| sp : ffffcd076afd3c80
| x29: ffffcd076afd3c80 x28: 0068000000000f07 x27: ffff800008000000
| x26: fffffbfff0000000 x25: fffffbffff000000 x24: ff00000000000000
| x23: ffffcd076ad3c000 x22: fffffc0000000000 x21: ffff800008000000
| x20: ffff800008004000 x19: ffff800008000000 x18: ffff800008004000
| x17: 666678302820295f x16: ffffffffffffffff x15: 0000000000000004
| x14: ffffcd076b009e88 x13: 0000000000000fff x12: 0000000000000003
| x11: 00000000ffffefff x10: c0000000ffffefff x9 : 0000000000000000
| x8 : 0000000000000000 x7 : 205d303030303030 x6 : 302e30202020205b
| x5 : ffffcd076b41d63f x4 : ffffcd076afd3827 x3 : 0000000000000000
| x2 : 0000000000000000 x1 : ffffcd076afd3a30 x0 : 000000000000004f
| Call trace:
|  __virt_to_phys+0x78/0x80
|  __kasan_unpoison_vmalloc+0xd4/0x478
|  __vmalloc_node_range+0x77c/0x7b8
|  __vmalloc_node+0x54/0x64
|  init_IRQ+0x94/0xc8
|  start_kernel+0x194/0x420
|  __primary_switched+0xbc/0xc4
| ---[ end trace 0000000000000000 ]---
| Unable to handle kernel paging request at virtual address 03fffacbe27b8000
| Mem abort info:
|   ESR = 0x0000000096000004
|   EC = 0x25: DABT (current EL), IL = 32 bits
|   SET = 0, FnV = 0
|   EA = 0, S1PTW = 0
|   FSC = 0x04: level 0 translation fault
| Data abort info:
|   ISV = 0, ISS = 0x00000004
|   CM = 0, WnR = 0
| swapper pgtable: 4k pages, 48-bit VAs, pgdp=0000000041bc5000
| [03fffacbe27b8000] pgd=0000000000000000, p4d=0000000000000000
| Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
| Modules linked in:
| CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W          6.3.0-rc3-00073-g83865133300d-dirty #4
| Hardware name: linux,dummy-virt (DT)
| pstate: 200000c5 (nzCv daIF -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : __kasan_unpoison_vmalloc+0xe4/0x478
| lr : __kasan_unpoison_vmalloc+0xd4/0x478
| sp : ffffcd076afd3ca0
| x29: ffffcd076afd3ca0 x28: 0068000000000f07 x27: ffff800008000000
| x26: 0000000000000000 x25: 03fffacbe27b8000 x24: ff00000000000000
| x23: ffffcd076ad3c000 x22: fffffc0000000000 x21: ffff800008000000
| x20: ffff800008004000 x19: ffff800008000000 x18: ffff800008004000
| x17: 666678302820295f x16: ffffffffffffffff x15: 0000000000000004
| x14: ffffcd076b009e88 x13: 0000000000000fff x12: 0000000000000001
| x11: 0000800008000000 x10: ffff800008000000 x9 : ffffb2f8dee00000
| x8 : 000ffffb2f8dee00 x7 : 205d303030303030 x6 : 302e30202020205b
| x5 : ffffcd076b41d63f x4 : ffffcd076afd3827 x3 : 0000000000000000
| x2 : 0000000000000000 x1 : ffffcd076afd3a30 x0 : ffffb2f8dee00000
| Call trace:
|  __kasan_unpoison_vmalloc+0xe4/0x478
|  __vmalloc_node_range+0x77c/0x7b8
|  __vmalloc_node+0x54/0x64
|  init_IRQ+0x94/0xc8
|  start_kernel+0x194/0x420
|  __primary_switched+0xbc/0xc4
| Code: d34cfc08 aa1f03fa 8b081b39 d503201f (f9400328)
| ---[ end trace 0000000000000000 ]---
| Kernel panic - not syncing: Attempted to kill the idle task!

This is because init_vmalloc_pages() erroneously calls virt_to_page() on
a vmalloc address, while virt_to_page() is only valid for addresses in
the linear/direct map. Since init_vmalloc_pages() expects virtual
addresses in the vmalloc range, it must use vmalloc_to_page() rather
than virt_to_page().

We call init_vmalloc_pages() from __kasan_unpoison_vmalloc(), where we
check !is_vmalloc_or_module_addr(), suggesting that we might encounter a
non-vmalloc address. Luckily, this never happens. By design, we only
call __kasan_unpoison_vmalloc() on pointers in the vmalloc area, and I
have verified that we don't violate that expectation. Given that,
is_vmalloc_or_module_addr() must always be true for any legitimate
argument to __kasan_unpoison_vmalloc().

Correct init_vmalloc_pages() to use vmalloc_to_page(), and remove the
redundant and misleading use of is_vmalloc_or_module_addr() in
__kasan_unpoison_vmalloc().

Fixes: 6c2f761dad7851d8 ("kasan: fix zeroing vmalloc memory with HW_TAGS")
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: kasan-dev@xxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx
---
 mm/kasan/hw_tags.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/kasan/hw_tags.c b/mm/kasan/hw_tags.c
index d1bcb0205327a..2f7ec2e1718ad 100644
--- a/mm/kasan/hw_tags.c
+++ b/mm/kasan/hw_tags.c
@@ -285,7 +285,7 @@ static void init_vmalloc_pages(const void *start, unsigned long size)
 	const void *addr;
 
 	for (addr = start; addr < start + size; addr += PAGE_SIZE) {
-		struct page *page = virt_to_page(addr);
+		struct page *page = vmalloc_to_page(addr);
 
 		clear_highpage_kasan_tagged(page);
 	}
@@ -297,7 +297,7 @@ void *__kasan_unpoison_vmalloc(const void *start, unsigned long size,
 	u8 tag;
 	unsigned long redzone_start, redzone_size;
 
-	if (!kasan_vmalloc_enabled() || !is_vmalloc_or_module_addr(start)) {
+	if (!kasan_vmalloc_enabled()) {
 		if (flags & KASAN_VMALLOC_INIT)
 			init_vmalloc_pages(start, size);
 		return (void *)start;
-- 
2.30.2