mm/alloc_tag: clear codetag for pages allocated before page_ext initialization

In the Linux kernel, the following vulnerability has been resolved:

mm/alloc_tag: clear codetag for pages allocated before page_ext initialization

Due to initialization ordering, page_ext is allocated and initialized

relatively late during boot. Some pages have already been allocated and

freed before page_ext becomes available, leaving their codetag

uninitialized.

A clear example is in init_section_page_ext(): alloc_page_ext() calls

kmemleak_alloc(). If the slab cache has no free objects, it falls back to

the buddy allocator to allocate memory. However, at this point page_ext

is not yet fully initialized, so these newly allocated pages have no

codetag set. These pages may later be reclaimed by KASAN, which causes

the warning to trigger when they are freed because their codetag ref is

still empty.

Use a global array to track pages allocated before page_ext is fully

initialized. The array size is fixed at 8192 entries, and will emit a

warning if this limit is exceeded. When page_ext initialization

completes, set their codetag to empty to avoid warnings when they are

freed later.

This warning is only observed with CONFIG_MEM_ALLOC_PROFILING_DEBUG=Y and

mem_profiling_compressed disabled:

[ 9.582133] ------------[ cut here ]------------

[ 9.582137] alloc_tag was not set

[ 9.582139] WARNING: ./include/linux/alloc_tag.h:164 at __pgalloc_tag_sub+0x40f/0x550, CPU#5: systemd/1

[ 9.582190] CPU: 5 UID: 0 PID: 1 Comm: systemd Not tainted 7.0.0-rc4 #1 PREEMPT(lazy)

[ 9.582192] Hardware name: Red Hat KVM, BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014

[ 9.582194] RIP: 0010:__pgalloc_tag_sub+0x40f/0x550

[ 9.582196] Code: 00 00 4c 29 e5 48 8b 05 1f 88 56 05 48 8d 4c ad 00 48 8d 2c c8 e9 87 fd ff ff 0f 0b 0f 0b e9 f3 fe ff ff 48 8d 3d 61 2f ed 03 <67> 48 0f b9 3a e9 b3 fd ff ff 0f 0b eb e4 e8 5e cd 14 02 4c 89 c7

[ 9.582197] RSP: 0018:ffffc9000001f940 EFLAGS: 00010246

[ 9.582200] RAX: dffffc0000000000 RBX: 1ffff92000003f2b RCX: 1ffff110200d806c

[ 9.582201] RDX: ffff8881006c0360 RSI: 0000000000000004 RDI: ffffffff9bc7b460

[ 9.582202] RBP: 0000000000000000 R08: 0000000000000000 R09: fffffbfff3a62324

[ 9.582203] R10: ffffffff9d311923 R11: 0000000000000000 R12: ffffea0004001b00

[ 9.582204] R13: 0000000000002000 R14: ffffea0000000000 R15: ffff8881006c0360

[ 9.582206] FS: 00007ffbbcf2d940(0000) GS:ffff888450479000(0000) knlGS:0000000000000000

[ 9.582208] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

[ 9.582210] CR2: 000055ee3aa260d0 CR3: 0000000148b67005 CR4: 0000000000770ef0

[ 9.582211] PKRU: 55555554

[ 9.582212] Call Trace:

[ 9.582213] <TASK>

[ 9.582214] ? __pfx___pgalloc_tag_sub+0x10/0x10

[ 9.582216] ? check_bytes_and_report+0x68/0x140

[ 9.582219] __free_frozen_pages+0x2e4/0x1150

[ 9.582221] ? __free_slab+0xc2/0x2b0

[ 9.582224] qlist_free_all+0x4c/0xf0

[ 9.582227] kasan_quarantine_reduce+0x15d/0x180

[ 9.582229] __kasan_slab_alloc+0x69/0x90

[ 9.582232] kmem_cache_alloc_noprof+0x14a/0x500

[ 9.582234] do_getname+0x96/0x310

[ 9.582237] do_readlinkat+0x91/0x2f0

[ 9.582239] ? __pfx_do_readlinkat+0x10/0x10

[ 9.582240] ? get_random_bytes_user+0x1df/0x2c0

[ 9.582244] __x64_sys_readlinkat+0x96/0x100

[ 9.582246] do_syscall_64+0xce/0x650

[ 9.582250] ? __x64_sys_getrandom+0x13a/0x1e0

[ 9.582252] ? __pfx___x64_sys_getrandom+0x10/0x10

[ 9.582254] ? do_syscall_64+0x114/0x650

[ 9.582255] ? ksys_read+0xfc/0x1d0

[ 9.582258] ? __pfx_ksys_read+0x10/0x10

[ 9.582260] ? do_syscall_64+0x114/0x650

[ 9.582262] ? do_syscall_64+0x114/0x650

[ 9.582264] ? __pfx_fput_close_sync+0x10/0x10

[ 9.582266] ? file_close_fd_locked+0x178/0x2a0

[ 9.582268] ? __x64_sys_faccessat2+0x96/0x100

[ 9.582269] ? __x64_sys_close+0x7d/0xd0

[ 9.582271] ? do_syscall_64+0x114/0x650

[ 9.582273] ? do_syscall_64+0x114/0x650

[ 9.582275] ? clear_bhb_loop+0x50/0xa0

[ 9.582277] ? clear_bhb_l

---truncated---