[PATCH v4] mm/alloc_tag: Fix panic when CONFIG_KASAN enabled and CONFIG_KASAN_VMALLOC not enabled

[Hao Ge <hao.ge@linux.dev>]

From: Hao Ge <gehao@kylinos.cn>

When CONFIG_KASAN is enabled but CONFIG_KASAN_VMALLOC
is not enabled, we may encounter a panic during system boot.

Because we haven't allocated pages and created mappings
for the shadow memory corresponding to module_tags region,
similar to how it is done for execmem_vmalloc.

The difference is that our module_tags are allocated on demand,
so similarly,we also need to allocate shadow memory regions on demand.
However, we still need to adhere to the MODULE_ALIGN principle.

Here is the log for panic:

[   18.349421] BUG: unable to handle page fault for address: fffffbfff8092000
[   18.350016] #PF: supervisor read access in kernel mode
[   18.350459] #PF: error_code(0x0000) - not-present page
[   18.350904] PGD 20fe52067 P4D 219dc8067 PUD 219dc4067 PMD 102495067 PTE 0
[   18.351484] Oops: Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
[   18.351961] CPU: 5 UID: 0 PID: 1 Comm: systemd Not tainted 6.13.0-rc1+ #3
[   18.352533] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   18.353494] RIP: 0010:kasan_check_range+0xba/0x1b0
[   18.353931] Code: 8d 5a 07 4c 0f 49 da 49 c1 fb 03 45 85 db 0f 84 dd 00 00 00 45 89 db 4a 8d 14 d8 eb 0d 48 83 c0 08 48 39 c2 0f 84 c1 00 00 00 <48> 83 38 00 74 ed 48 8d 50 08 eb 0d 48 83 c0 01 48 39 d0 0f 84 90
[   18.355484] RSP: 0018:ff11000101877958 EFLAGS: 00010206
[   18.355937] RAX: fffffbfff8092000 RBX: fffffbfff809201e RCX: ffffffff82a7ceac
[   18.356542] RDX: fffffbfff8092018 RSI: 00000000000000f0 RDI: ffffffffc0490000
[   18.357153] RBP: fffffbfff8092000 R08: 0000000000000001 R09: fffffbfff809201d
[   18.357756] R10: ffffffffc04900ef R11: 0000000000000003 R12: ffffffffc0490000
[   18.358365] R13: ff11000101877b48 R14: ffffffffc0490000 R15: 000000000000002c
[   18.358968] FS:  00007f9bd13c5940(0000) GS:ff110001eb480000(0000) knlGS:0000000000000000
[   18.359648] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   18.360178] CR2: fffffbfff8092000 CR3: 0000000109214004 CR4: 0000000000771ef0
[   18.360790] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[   18.361404] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[   18.362020] PKRU: 55555554
[   18.362261] Call Trace:
[   18.362481]  <TASK>
[   18.362671]  ? __die+0x23/0x70
[   18.362964]  ? page_fault_oops+0xc2/0x160
[   18.363318]  ? exc_page_fault+0xad/0xc0
[   18.363680]  ? asm_exc_page_fault+0x26/0x30
[   18.364056]  ? move_module+0x3cc/0x8a0
[   18.364398]  ? kasan_check_range+0xba/0x1b0
[   18.364755]  __asan_memcpy+0x3c/0x60
[   18.365074]  move_module+0x3cc/0x8a0
[   18.365386]  layout_and_allocate.constprop.0+0x3d5/0x720
[   18.365841]  ? early_mod_check+0x3dc/0x510
[   18.366195]  load_module+0x72/0x1850
[   18.366509]  ? __pfx_kernel_read_file+0x10/0x10
[   18.366918]  ? vm_mmap_pgoff+0x21c/0x2d0
[   18.367262]  init_module_from_file+0xd1/0x130
[   18.367638]  ? __pfx_init_module_from_file+0x10/0x10
[   18.368073]  ? __pfx__raw_spin_lock+0x10/0x10
[   18.368456]  ? __pfx_cred_has_capability.isra.0+0x10/0x10
[   18.368938]  idempotent_init_module+0x22c/0x790
[   18.369332]  ? simple_getattr+0x6f/0x120
[   18.369676]  ? __pfx_idempotent_init_module+0x10/0x10
[   18.370110]  ? fdget+0x58/0x3a0
[   18.370393]  ? security_capable+0x64/0xf0
[   18.370745]  __x64_sys_finit_module+0xc2/0x140
[   18.371136]  do_syscall_64+0x7d/0x160
[   18.371459]  ? fdget_pos+0x1c8/0x4c0
[   18.371784]  ? ksys_read+0xfd/0x1d0
[   18.372106]  ? syscall_exit_to_user_mode+0x10/0x1f0
[   18.372525]  ? do_syscall_64+0x89/0x160
[   18.372860]  ? do_syscall_64+0x89/0x160
[   18.373194]  ? do_syscall_64+0x89/0x160
[   18.373527]  ? syscall_exit_to_user_mode+0x10/0x1f0
[   18.373952]  ? do_syscall_64+0x89/0x160
[   18.374283]  ? syscall_exit_to_user_mode+0x10/0x1f0
[   18.374701]  ? do_syscall_64+0x89/0x160
[   18.375037]  ? do_user_addr_fault+0x4a8/0xa40
[   18.375416]  ? clear_bhb_loop+0x25/0x80
[   18.375748]  ? clear_bhb_loop+0x25/0x80
[   18.376119]  ? clear_bhb_loop+0x25/0x80
[   18.376450]  entry_SYSCALL_64_after_hwframe+0x76/0x7e

Fixes: 233e89322cbe ("alloc_tag: fix module allocation tags populated area calculation")
Reported-by: Ben Greear <greearb@candelatech.com>
Closes: https://lore.kernel.org/all/1ba0cc57-e2ed-caa2-1241-aa5615bee01f@candelatech.com/
Suggested-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Hao Ge <gehao@kylinos.cn>
---
v4: Based on Suren's suggestion for modification (to make the code simpler),
    modify the code.
    Update the comments in the code due to the modifications made to the code.
    Add Suggested-by: Suren Baghdasaryan <surenb@google.com>

v3: Adjusting the title because the previous one was a bit unclear.
    Suren has pointed out that our condition for determining whether
    to allocate shadow memory is unreasonable.We have adjusted our method
    to use every 8 pages as an index (idx), and we will make decisions based
    on this idx when determining whether to allocate shadow memory.

v2: Add comments to facilitate understanding of the code.
    Add align nr << PAGE_SHIFT to MODULE_ALIGN,even though kasan_alloc_module_shadow
    already handles this internally,but to make the code more readable and user-friendly

commit 233e89322cbe ("alloc_tag: fix module allocation
tags populated area calculation") is currently in the
mm-hotfixes-unstable branch, so this patch is
developed based on the mm-hotfixes-unstable branch.
---
 lib/alloc_tag.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index f942408b53ef..c5bdfa297a35 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -407,6 +407,8 @@ static int vm_module_tags_populate(void)
 
 	if (phys_end < new_end) {
 		struct page **next_page = vm_module_tags->pages + vm_module_tags->nr_pages;
+		unsigned long old_shadow_end = ALIGN(phys_end, MODULE_ALIGN);
+		unsigned long new_shadow_end = ALIGN(new_end, MODULE_ALIGN);
 		unsigned long more_pages;
 		unsigned long nr;
 
@@ -421,7 +423,19 @@ static int vm_module_tags_populate(void)
 				__free_page(next_page[i]);
 			return -ENOMEM;
 		}
+
 		vm_module_tags->nr_pages += nr;
+
+		/*
+		 * Kasan allocates 1 byte of shadow for every 8 bytes of data.
+		 * When kasan_alloc_module_shadow allocates shadow memory,
+		 * its unit of allocation is a page.
+		 * Therefore, here we need to align to MODULE_ALIGN.
+		 */
+		if (old_shadow_end < new_shadow_end)
+			kasan_alloc_module_shadow((void *)old_shadow_end,
+						  new_shadow_end - old_shadow_end,
+						  GFP_KERNEL);
 	}
 
 	/*
-- 
2.25.1