Unrated severityNVD Advisory· Published Jun 8, 2026
CVE-2026-46279
CVE-2026-46279
Description
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] [ 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---
Affected products
1Patches
6b49dfabc38camm/alloc_tag: clear codetag for pages allocated before page_ext initialization
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.gitHao GeMar 31, 2026Fixed in 7.0.4via kernel-cna
4 files changed · +121 −3
include/linux/alloc_tag.h+2 −0 modifieddiff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h index d40ac39bfbe8d..02de2ede560f3 100644 --- a/include/linux/alloc_tag.h +++ b/include/linux/alloc_tag.h @@ -163,9 +163,11 @@ static inline void alloc_tag_sub_check(union codetag_ref *ref) { WARN_ONCE(ref && !ref->ct, "alloc_tag was not set\n"); } +void alloc_tag_add_early_pfn(unsigned long pfn); #else static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag) {} static inline void alloc_tag_sub_check(union codetag_ref *ref) {} +static inline void alloc_tag_add_early_pfn(unsigned long pfn) {} #endif /* Caller should verify both ref and tag to be valid */
include/linux/pgalloc_tag.h+1 −1 modifieddiff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h index 38a82d65e58e9..951d333622685 100644 --- a/include/linux/pgalloc_tag.h +++ b/include/linux/pgalloc_tag.h @@ -181,7 +181,7 @@ static inline struct alloc_tag *__pgalloc_tag_get(struct page *page) if (get_page_tag_ref(page, &ref, &handle)) { alloc_tag_sub_check(&ref); - if (ref.ct) + if (ref.ct && !is_codetag_empty(&ref)) tag = ct_to_alloc_tag(ref.ct); put_page_tag_ref(handle); }
lib/alloc_tag.c+109 −0 modifieddiff --git a/lib/alloc_tag.c b/lib/alloc_tag.c index 58991ab09d84b..ed1bdcf1f8abf 100644 --- a/lib/alloc_tag.c +++ b/lib/alloc_tag.c @@ -6,7 +6,9 @@ #include <linux/kallsyms.h> #include <linux/module.h> #include <linux/page_ext.h> +#include <linux/pgalloc_tag.h> #include <linux/proc_fs.h> +#include <linux/rcupdate.h> #include <linux/seq_buf.h> #include <linux/seq_file.h> #include <linux/string_choices.h> @@ -758,8 +760,115 @@ static __init bool need_page_alloc_tagging(void) return mem_profiling_support; } +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG +/* + * Track page allocations before page_ext is initialized. + * Some pages are allocated before page_ext becomes available, leaving + * their codetag uninitialized. Track these early PFNs so we can clear + * their codetag refs later to avoid warnings when they are freed. + * + * Early allocations include: + * - Base allocations independent of CPU count + * - Per-CPU allocations (e.g., CPU hotplug callbacks during smp_init, + * such as trace ring buffers, scheduler per-cpu data) + * + * For simplicity, we fix the size to 8192. + * If insufficient, a warning will be triggered to alert the user. + * + * TODO: Replace fixed-size array with dynamic allocation using + * a GFP flag similar to ___GFP_NO_OBJ_EXT to avoid recursion. + */ +#define EARLY_ALLOC_PFN_MAX 8192 + +static unsigned long early_pfns[EARLY_ALLOC_PFN_MAX] __initdata; +static atomic_t early_pfn_count __initdata = ATOMIC_INIT(0); + +static void __init __alloc_tag_add_early_pfn(unsigned long pfn) +{ + int old_idx, new_idx; + + do { + old_idx = atomic_read(&early_pfn_count); + if (old_idx >= EARLY_ALLOC_PFN_MAX) { + pr_warn_once("Early page allocations before page_ext init exceeded EARLY_ALLOC_PFN_MAX (%d)\n", + EARLY_ALLOC_PFN_MAX); + return; + } + new_idx = old_idx + 1; + } while (!atomic_try_cmpxchg(&early_pfn_count, &old_idx, new_idx)); + + early_pfns[old_idx] = pfn; +} + +typedef void alloc_tag_add_func(unsigned long pfn); +static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata = + RCU_INITIALIZER(__alloc_tag_add_early_pfn); + +void alloc_tag_add_early_pfn(unsigned long pfn) +{ + alloc_tag_add_func *alloc_tag_add; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_read_lock(); + alloc_tag_add = rcu_dereference(alloc_tag_add_early_pfn_ptr); + if (alloc_tag_add) + alloc_tag_add(pfn); + rcu_read_unlock(); +} + +static void __init clear_early_alloc_pfn_tag_refs(void) +{ + unsigned int i; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_assign_pointer(alloc_tag_add_early_pfn_ptr, NULL); + /* Make sure we are not racing with __alloc_tag_add_early_pfn() */ + synchronize_rcu(); + + for (i = 0; i < atomic_read(&early_pfn_count); i++) { + unsigned long pfn = early_pfns[i]; + + if (pfn_valid(pfn)) { + struct page *page = pfn_to_page(pfn); + union pgtag_ref_handle handle; + union codetag_ref ref; + + if (get_page_tag_ref(page, &ref, &handle)) { + /* + * An early-allocated page could be freed and reallocated + * after its page_ext is initialized but before we clear it. + * In that case, it already has a valid tag set. + * We should not overwrite that valid tag with CODETAG_EMPTY. + * + * Note: there is still a small race window between checking + * ref.ct and calling set_codetag_empty(). We accept this + * race as it's unlikely and the extra complexity of atomic + * cmpxchg is not worth it for this debug-only code path. + */ + if (ref.ct) { + put_page_tag_ref(handle); + continue; + } + + set_codetag_empty(&ref); + update_page_tag_ref(handle, &ref); + put_page_tag_ref(handle); + } + } + + } +} +#else /* !CONFIG_MEM_ALLOC_PROFILING_DEBUG */ +static inline void __init clear_early_alloc_pfn_tag_refs(void) {} +#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */ + static __init void init_page_alloc_tagging(void) { + clear_early_alloc_pfn_tag_refs(); } struct page_ext_operations page_alloc_tagging_ops = {
mm/page_alloc.c+9 −2 modifieddiff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2d4b6f1a554ed..04494bc2e46f9 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1289,10 +1289,18 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task, union pgtag_ref_handle handle; union codetag_ref ref; - if (get_page_tag_ref(page, &ref, &handle)) { + if (likely(get_page_tag_ref(page, &ref, &handle))) { alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr); update_page_tag_ref(handle, &ref); put_page_tag_ref(handle); + } else { + /* + * page_ext is not available yet, record the pfn so we can + * clear the tag ref later when page_ext is initialized. + */ + alloc_tag_add_early_pfn(page_to_pfn(page)); + if (task->alloc_tag) + alloc_tag_set_inaccurate(task->alloc_tag); } } -- cgit 1.3-korg
d5b495ba9de0mm/alloc_tag: clear codetag for pages allocated before page_ext initialization
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.gitHao GeMar 31, 2026Fixed in 6.18.27via kernel-cna
4 files changed · +121 −3
include/linux/alloc_tag.h+2 −0 modifieddiff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h index d40ac39bfbe8d..02de2ede560f3 100644 --- a/include/linux/alloc_tag.h +++ b/include/linux/alloc_tag.h @@ -163,9 +163,11 @@ static inline void alloc_tag_sub_check(union codetag_ref *ref) { WARN_ONCE(ref && !ref->ct, "alloc_tag was not set\n"); } +void alloc_tag_add_early_pfn(unsigned long pfn); #else static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag) {} static inline void alloc_tag_sub_check(union codetag_ref *ref) {} +static inline void alloc_tag_add_early_pfn(unsigned long pfn) {} #endif /* Caller should verify both ref and tag to be valid */
include/linux/pgalloc_tag.h+1 −1 modifieddiff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h index 38a82d65e58e9..951d333622685 100644 --- a/include/linux/pgalloc_tag.h +++ b/include/linux/pgalloc_tag.h @@ -181,7 +181,7 @@ static inline struct alloc_tag *__pgalloc_tag_get(struct page *page) if (get_page_tag_ref(page, &ref, &handle)) { alloc_tag_sub_check(&ref); - if (ref.ct) + if (ref.ct && !is_codetag_empty(&ref)) tag = ct_to_alloc_tag(ref.ct); put_page_tag_ref(handle); }
lib/alloc_tag.c+109 −0 modifieddiff --git a/lib/alloc_tag.c b/lib/alloc_tag.c index f26456988445b..df6ba06a8e4a8 100644 --- a/lib/alloc_tag.c +++ b/lib/alloc_tag.c @@ -6,7 +6,9 @@ #include <linux/kallsyms.h> #include <linux/module.h> #include <linux/page_ext.h> +#include <linux/pgalloc_tag.h> #include <linux/proc_fs.h> +#include <linux/rcupdate.h> #include <linux/seq_buf.h> #include <linux/seq_file.h> #include <linux/string_choices.h> @@ -757,8 +759,115 @@ static __init bool need_page_alloc_tagging(void) return mem_profiling_support; } +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG +/* + * Track page allocations before page_ext is initialized. + * Some pages are allocated before page_ext becomes available, leaving + * their codetag uninitialized. Track these early PFNs so we can clear + * their codetag refs later to avoid warnings when they are freed. + * + * Early allocations include: + * - Base allocations independent of CPU count + * - Per-CPU allocations (e.g., CPU hotplug callbacks during smp_init, + * such as trace ring buffers, scheduler per-cpu data) + * + * For simplicity, we fix the size to 8192. + * If insufficient, a warning will be triggered to alert the user. + * + * TODO: Replace fixed-size array with dynamic allocation using + * a GFP flag similar to ___GFP_NO_OBJ_EXT to avoid recursion. + */ +#define EARLY_ALLOC_PFN_MAX 8192 + +static unsigned long early_pfns[EARLY_ALLOC_PFN_MAX] __initdata; +static atomic_t early_pfn_count __initdata = ATOMIC_INIT(0); + +static void __init __alloc_tag_add_early_pfn(unsigned long pfn) +{ + int old_idx, new_idx; + + do { + old_idx = atomic_read(&early_pfn_count); + if (old_idx >= EARLY_ALLOC_PFN_MAX) { + pr_warn_once("Early page allocations before page_ext init exceeded EARLY_ALLOC_PFN_MAX (%d)\n", + EARLY_ALLOC_PFN_MAX); + return; + } + new_idx = old_idx + 1; + } while (!atomic_try_cmpxchg(&early_pfn_count, &old_idx, new_idx)); + + early_pfns[old_idx] = pfn; +} + +typedef void alloc_tag_add_func(unsigned long pfn); +static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata = + RCU_INITIALIZER(__alloc_tag_add_early_pfn); + +void alloc_tag_add_early_pfn(unsigned long pfn) +{ + alloc_tag_add_func *alloc_tag_add; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_read_lock(); + alloc_tag_add = rcu_dereference(alloc_tag_add_early_pfn_ptr); + if (alloc_tag_add) + alloc_tag_add(pfn); + rcu_read_unlock(); +} + +static void __init clear_early_alloc_pfn_tag_refs(void) +{ + unsigned int i; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_assign_pointer(alloc_tag_add_early_pfn_ptr, NULL); + /* Make sure we are not racing with __alloc_tag_add_early_pfn() */ + synchronize_rcu(); + + for (i = 0; i < atomic_read(&early_pfn_count); i++) { + unsigned long pfn = early_pfns[i]; + + if (pfn_valid(pfn)) { + struct page *page = pfn_to_page(pfn); + union pgtag_ref_handle handle; + union codetag_ref ref; + + if (get_page_tag_ref(page, &ref, &handle)) { + /* + * An early-allocated page could be freed and reallocated + * after its page_ext is initialized but before we clear it. + * In that case, it already has a valid tag set. + * We should not overwrite that valid tag with CODETAG_EMPTY. + * + * Note: there is still a small race window between checking + * ref.ct and calling set_codetag_empty(). We accept this + * race as it's unlikely and the extra complexity of atomic + * cmpxchg is not worth it for this debug-only code path. + */ + if (ref.ct) { + put_page_tag_ref(handle); + continue; + } + + set_codetag_empty(&ref); + update_page_tag_ref(handle, &ref); + put_page_tag_ref(handle); + } + } + + } +} +#else /* !CONFIG_MEM_ALLOC_PROFILING_DEBUG */ +static inline void __init clear_early_alloc_pfn_tag_refs(void) {} +#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */ + static __init void init_page_alloc_tagging(void) { + clear_early_alloc_pfn_tag_refs(); } struct page_ext_operations page_alloc_tagging_ops = {
mm/page_alloc.c+9 −2 modifieddiff --git a/mm/page_alloc.c b/mm/page_alloc.c index 6288c7e4b971b..43363fd3b8ea4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1289,10 +1289,18 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task, union pgtag_ref_handle handle; union codetag_ref ref; - if (get_page_tag_ref(page, &ref, &handle)) { + if (likely(get_page_tag_ref(page, &ref, &handle))) { alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr); update_page_tag_ref(handle, &ref); put_page_tag_ref(handle); + } else { + /* + * page_ext is not available yet, record the pfn so we can + * clear the tag ref later when page_ext is initialized. + */ + alloc_tag_add_early_pfn(page_to_pfn(page)); + if (task->alloc_tag) + alloc_tag_set_inaccurate(task->alloc_tag); } } -- cgit 1.3-korg
6b1842775a46mm/alloc_tag: clear codetag for pages allocated before page_ext initialization
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.gitHao GeMar 31, 2026Fixed in 7.1-rc1via kernel-cna
4 files changed · +121 −3
include/linux/alloc_tag.h+2 −0 modifieddiff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h index d40ac39bfbe8d..02de2ede560f3 100644 --- a/include/linux/alloc_tag.h +++ b/include/linux/alloc_tag.h @@ -163,9 +163,11 @@ static inline void alloc_tag_sub_check(union codetag_ref *ref) { WARN_ONCE(ref && !ref->ct, "alloc_tag was not set\n"); } +void alloc_tag_add_early_pfn(unsigned long pfn); #else static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag) {} static inline void alloc_tag_sub_check(union codetag_ref *ref) {} +static inline void alloc_tag_add_early_pfn(unsigned long pfn) {} #endif /* Caller should verify both ref and tag to be valid */
include/linux/pgalloc_tag.h+1 −1 modifieddiff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h index 38a82d65e58e9..951d333622685 100644 --- a/include/linux/pgalloc_tag.h +++ b/include/linux/pgalloc_tag.h @@ -181,7 +181,7 @@ static inline struct alloc_tag *__pgalloc_tag_get(struct page *page) if (get_page_tag_ref(page, &ref, &handle)) { alloc_tag_sub_check(&ref); - if (ref.ct) + if (ref.ct && !is_codetag_empty(&ref)) tag = ct_to_alloc_tag(ref.ct); put_page_tag_ref(handle); }
lib/alloc_tag.c+109 −0 modifieddiff --git a/lib/alloc_tag.c b/lib/alloc_tag.c index 58991ab09d84b..ed1bdcf1f8abf 100644 --- a/lib/alloc_tag.c +++ b/lib/alloc_tag.c @@ -6,7 +6,9 @@ #include <linux/kallsyms.h> #include <linux/module.h> #include <linux/page_ext.h> +#include <linux/pgalloc_tag.h> #include <linux/proc_fs.h> +#include <linux/rcupdate.h> #include <linux/seq_buf.h> #include <linux/seq_file.h> #include <linux/string_choices.h> @@ -758,8 +760,115 @@ static __init bool need_page_alloc_tagging(void) return mem_profiling_support; } +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG +/* + * Track page allocations before page_ext is initialized. + * Some pages are allocated before page_ext becomes available, leaving + * their codetag uninitialized. Track these early PFNs so we can clear + * their codetag refs later to avoid warnings when they are freed. + * + * Early allocations include: + * - Base allocations independent of CPU count + * - Per-CPU allocations (e.g., CPU hotplug callbacks during smp_init, + * such as trace ring buffers, scheduler per-cpu data) + * + * For simplicity, we fix the size to 8192. + * If insufficient, a warning will be triggered to alert the user. + * + * TODO: Replace fixed-size array with dynamic allocation using + * a GFP flag similar to ___GFP_NO_OBJ_EXT to avoid recursion. + */ +#define EARLY_ALLOC_PFN_MAX 8192 + +static unsigned long early_pfns[EARLY_ALLOC_PFN_MAX] __initdata; +static atomic_t early_pfn_count __initdata = ATOMIC_INIT(0); + +static void __init __alloc_tag_add_early_pfn(unsigned long pfn) +{ + int old_idx, new_idx; + + do { + old_idx = atomic_read(&early_pfn_count); + if (old_idx >= EARLY_ALLOC_PFN_MAX) { + pr_warn_once("Early page allocations before page_ext init exceeded EARLY_ALLOC_PFN_MAX (%d)\n", + EARLY_ALLOC_PFN_MAX); + return; + } + new_idx = old_idx + 1; + } while (!atomic_try_cmpxchg(&early_pfn_count, &old_idx, new_idx)); + + early_pfns[old_idx] = pfn; +} + +typedef void alloc_tag_add_func(unsigned long pfn); +static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata = + RCU_INITIALIZER(__alloc_tag_add_early_pfn); + +void alloc_tag_add_early_pfn(unsigned long pfn) +{ + alloc_tag_add_func *alloc_tag_add; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_read_lock(); + alloc_tag_add = rcu_dereference(alloc_tag_add_early_pfn_ptr); + if (alloc_tag_add) + alloc_tag_add(pfn); + rcu_read_unlock(); +} + +static void __init clear_early_alloc_pfn_tag_refs(void) +{ + unsigned int i; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_assign_pointer(alloc_tag_add_early_pfn_ptr, NULL); + /* Make sure we are not racing with __alloc_tag_add_early_pfn() */ + synchronize_rcu(); + + for (i = 0; i < atomic_read(&early_pfn_count); i++) { + unsigned long pfn = early_pfns[i]; + + if (pfn_valid(pfn)) { + struct page *page = pfn_to_page(pfn); + union pgtag_ref_handle handle; + union codetag_ref ref; + + if (get_page_tag_ref(page, &ref, &handle)) { + /* + * An early-allocated page could be freed and reallocated + * after its page_ext is initialized but before we clear it. + * In that case, it already has a valid tag set. + * We should not overwrite that valid tag with CODETAG_EMPTY. + * + * Note: there is still a small race window between checking + * ref.ct and calling set_codetag_empty(). We accept this + * race as it's unlikely and the extra complexity of atomic + * cmpxchg is not worth it for this debug-only code path. + */ + if (ref.ct) { + put_page_tag_ref(handle); + continue; + } + + set_codetag_empty(&ref); + update_page_tag_ref(handle, &ref); + put_page_tag_ref(handle); + } + } + + } +} +#else /* !CONFIG_MEM_ALLOC_PROFILING_DEBUG */ +static inline void __init clear_early_alloc_pfn_tag_refs(void) {} +#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */ + static __init void init_page_alloc_tagging(void) { + clear_early_alloc_pfn_tag_refs(); } struct page_ext_operations page_alloc_tagging_ops = {
mm/page_alloc.c+9 −2 modifieddiff --git a/mm/page_alloc.c b/mm/page_alloc.c index 111b54df8a3cb..b1c5430cad4e5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1252,10 +1252,18 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task, union pgtag_ref_handle handle; union codetag_ref ref; - if (get_page_tag_ref(page, &ref, &handle)) { + if (likely(get_page_tag_ref(page, &ref, &handle))) { alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr); update_page_tag_ref(handle, &ref); put_page_tag_ref(handle); + } else { + /* + * page_ext is not available yet, record the pfn so we can + * clear the tag ref later when page_ext is initialized. + */ + alloc_tag_add_early_pfn(page_to_pfn(page)); + if (task->alloc_tag) + alloc_tag_set_inaccurate(task->alloc_tag); } } -- cgit 1.3-korg
d5b495ba9de0mm/alloc_tag: clear codetag for pages allocated before page_ext initialization
4 files changed · +121 −3
include/linux/alloc_tag.h+2 −0 modifieddiff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h index d40ac39bfbe8d..02de2ede560f3 100644 --- a/include/linux/alloc_tag.h +++ b/include/linux/alloc_tag.h @@ -163,9 +163,11 @@ static inline void alloc_tag_sub_check(union codetag_ref *ref) { WARN_ONCE(ref && !ref->ct, "alloc_tag was not set\n"); } +void alloc_tag_add_early_pfn(unsigned long pfn); #else static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag) {} static inline void alloc_tag_sub_check(union codetag_ref *ref) {} +static inline void alloc_tag_add_early_pfn(unsigned long pfn) {} #endif /* Caller should verify both ref and tag to be valid */
include/linux/pgalloc_tag.h+1 −1 modifieddiff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h index 38a82d65e58e9..951d333622685 100644 --- a/include/linux/pgalloc_tag.h +++ b/include/linux/pgalloc_tag.h @@ -181,7 +181,7 @@ static inline struct alloc_tag *__pgalloc_tag_get(struct page *page) if (get_page_tag_ref(page, &ref, &handle)) { alloc_tag_sub_check(&ref); - if (ref.ct) + if (ref.ct && !is_codetag_empty(&ref)) tag = ct_to_alloc_tag(ref.ct); put_page_tag_ref(handle); }
lib/alloc_tag.c+109 −0 modifieddiff --git a/lib/alloc_tag.c b/lib/alloc_tag.c index f26456988445b..df6ba06a8e4a8 100644 --- a/lib/alloc_tag.c +++ b/lib/alloc_tag.c @@ -6,7 +6,9 @@ #include <linux/kallsyms.h> #include <linux/module.h> #include <linux/page_ext.h> +#include <linux/pgalloc_tag.h> #include <linux/proc_fs.h> +#include <linux/rcupdate.h> #include <linux/seq_buf.h> #include <linux/seq_file.h> #include <linux/string_choices.h> @@ -757,8 +759,115 @@ static __init bool need_page_alloc_tagging(void) return mem_profiling_support; } +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG +/* + * Track page allocations before page_ext is initialized. + * Some pages are allocated before page_ext becomes available, leaving + * their codetag uninitialized. Track these early PFNs so we can clear + * their codetag refs later to avoid warnings when they are freed. + * + * Early allocations include: + * - Base allocations independent of CPU count + * - Per-CPU allocations (e.g., CPU hotplug callbacks during smp_init, + * such as trace ring buffers, scheduler per-cpu data) + * + * For simplicity, we fix the size to 8192. + * If insufficient, a warning will be triggered to alert the user. + * + * TODO: Replace fixed-size array with dynamic allocation using + * a GFP flag similar to ___GFP_NO_OBJ_EXT to avoid recursion. + */ +#define EARLY_ALLOC_PFN_MAX 8192 + +static unsigned long early_pfns[EARLY_ALLOC_PFN_MAX] __initdata; +static atomic_t early_pfn_count __initdata = ATOMIC_INIT(0); + +static void __init __alloc_tag_add_early_pfn(unsigned long pfn) +{ + int old_idx, new_idx; + + do { + old_idx = atomic_read(&early_pfn_count); + if (old_idx >= EARLY_ALLOC_PFN_MAX) { + pr_warn_once("Early page allocations before page_ext init exceeded EARLY_ALLOC_PFN_MAX (%d)\n", + EARLY_ALLOC_PFN_MAX); + return; + } + new_idx = old_idx + 1; + } while (!atomic_try_cmpxchg(&early_pfn_count, &old_idx, new_idx)); + + early_pfns[old_idx] = pfn; +} + +typedef void alloc_tag_add_func(unsigned long pfn); +static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata = + RCU_INITIALIZER(__alloc_tag_add_early_pfn); + +void alloc_tag_add_early_pfn(unsigned long pfn) +{ + alloc_tag_add_func *alloc_tag_add; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_read_lock(); + alloc_tag_add = rcu_dereference(alloc_tag_add_early_pfn_ptr); + if (alloc_tag_add) + alloc_tag_add(pfn); + rcu_read_unlock(); +} + +static void __init clear_early_alloc_pfn_tag_refs(void) +{ + unsigned int i; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_assign_pointer(alloc_tag_add_early_pfn_ptr, NULL); + /* Make sure we are not racing with __alloc_tag_add_early_pfn() */ + synchronize_rcu(); + + for (i = 0; i < atomic_read(&early_pfn_count); i++) { + unsigned long pfn = early_pfns[i]; + + if (pfn_valid(pfn)) { + struct page *page = pfn_to_page(pfn); + union pgtag_ref_handle handle; + union codetag_ref ref; + + if (get_page_tag_ref(page, &ref, &handle)) { + /* + * An early-allocated page could be freed and reallocated + * after its page_ext is initialized but before we clear it. + * In that case, it already has a valid tag set. + * We should not overwrite that valid tag with CODETAG_EMPTY. + * + * Note: there is still a small race window between checking + * ref.ct and calling set_codetag_empty(). We accept this + * race as it's unlikely and the extra complexity of atomic + * cmpxchg is not worth it for this debug-only code path. + */ + if (ref.ct) { + put_page_tag_ref(handle); + continue; + } + + set_codetag_empty(&ref); + update_page_tag_ref(handle, &ref); + put_page_tag_ref(handle); + } + } + + } +} +#else /* !CONFIG_MEM_ALLOC_PROFILING_DEBUG */ +static inline void __init clear_early_alloc_pfn_tag_refs(void) {} +#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */ + static __init void init_page_alloc_tagging(void) { + clear_early_alloc_pfn_tag_refs(); } struct page_ext_operations page_alloc_tagging_ops = {
mm/page_alloc.c+9 −2 modifieddiff --git a/mm/page_alloc.c b/mm/page_alloc.c index 6288c7e4b971b..43363fd3b8ea4 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1289,10 +1289,18 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task, union pgtag_ref_handle handle; union codetag_ref ref; - if (get_page_tag_ref(page, &ref, &handle)) { + if (likely(get_page_tag_ref(page, &ref, &handle))) { alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr); update_page_tag_ref(handle, &ref); put_page_tag_ref(handle); + } else { + /* + * page_ext is not available yet, record the pfn so we can + * clear the tag ref later when page_ext is initialized. + */ + alloc_tag_add_early_pfn(page_to_pfn(page)); + if (task->alloc_tag) + alloc_tag_set_inaccurate(task->alloc_tag); } } -- cgit 1.3-korg
b49dfabc38camm/alloc_tag: clear codetag for pages allocated before page_ext initialization
4 files changed · +121 −3
include/linux/alloc_tag.h+2 −0 modifieddiff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h index d40ac39bfbe8d..02de2ede560f3 100644 --- a/include/linux/alloc_tag.h +++ b/include/linux/alloc_tag.h @@ -163,9 +163,11 @@ static inline void alloc_tag_sub_check(union codetag_ref *ref) { WARN_ONCE(ref && !ref->ct, "alloc_tag was not set\n"); } +void alloc_tag_add_early_pfn(unsigned long pfn); #else static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag) {} static inline void alloc_tag_sub_check(union codetag_ref *ref) {} +static inline void alloc_tag_add_early_pfn(unsigned long pfn) {} #endif /* Caller should verify both ref and tag to be valid */
include/linux/pgalloc_tag.h+1 −1 modifieddiff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h index 38a82d65e58e9..951d333622685 100644 --- a/include/linux/pgalloc_tag.h +++ b/include/linux/pgalloc_tag.h @@ -181,7 +181,7 @@ static inline struct alloc_tag *__pgalloc_tag_get(struct page *page) if (get_page_tag_ref(page, &ref, &handle)) { alloc_tag_sub_check(&ref); - if (ref.ct) + if (ref.ct && !is_codetag_empty(&ref)) tag = ct_to_alloc_tag(ref.ct); put_page_tag_ref(handle); }
lib/alloc_tag.c+109 −0 modifieddiff --git a/lib/alloc_tag.c b/lib/alloc_tag.c index 58991ab09d84b..ed1bdcf1f8abf 100644 --- a/lib/alloc_tag.c +++ b/lib/alloc_tag.c @@ -6,7 +6,9 @@ #include <linux/kallsyms.h> #include <linux/module.h> #include <linux/page_ext.h> +#include <linux/pgalloc_tag.h> #include <linux/proc_fs.h> +#include <linux/rcupdate.h> #include <linux/seq_buf.h> #include <linux/seq_file.h> #include <linux/string_choices.h> @@ -758,8 +760,115 @@ static __init bool need_page_alloc_tagging(void) return mem_profiling_support; } +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG +/* + * Track page allocations before page_ext is initialized. + * Some pages are allocated before page_ext becomes available, leaving + * their codetag uninitialized. Track these early PFNs so we can clear + * their codetag refs later to avoid warnings when they are freed. + * + * Early allocations include: + * - Base allocations independent of CPU count + * - Per-CPU allocations (e.g., CPU hotplug callbacks during smp_init, + * such as trace ring buffers, scheduler per-cpu data) + * + * For simplicity, we fix the size to 8192. + * If insufficient, a warning will be triggered to alert the user. + * + * TODO: Replace fixed-size array with dynamic allocation using + * a GFP flag similar to ___GFP_NO_OBJ_EXT to avoid recursion. + */ +#define EARLY_ALLOC_PFN_MAX 8192 + +static unsigned long early_pfns[EARLY_ALLOC_PFN_MAX] __initdata; +static atomic_t early_pfn_count __initdata = ATOMIC_INIT(0); + +static void __init __alloc_tag_add_early_pfn(unsigned long pfn) +{ + int old_idx, new_idx; + + do { + old_idx = atomic_read(&early_pfn_count); + if (old_idx >= EARLY_ALLOC_PFN_MAX) { + pr_warn_once("Early page allocations before page_ext init exceeded EARLY_ALLOC_PFN_MAX (%d)\n", + EARLY_ALLOC_PFN_MAX); + return; + } + new_idx = old_idx + 1; + } while (!atomic_try_cmpxchg(&early_pfn_count, &old_idx, new_idx)); + + early_pfns[old_idx] = pfn; +} + +typedef void alloc_tag_add_func(unsigned long pfn); +static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata = + RCU_INITIALIZER(__alloc_tag_add_early_pfn); + +void alloc_tag_add_early_pfn(unsigned long pfn) +{ + alloc_tag_add_func *alloc_tag_add; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_read_lock(); + alloc_tag_add = rcu_dereference(alloc_tag_add_early_pfn_ptr); + if (alloc_tag_add) + alloc_tag_add(pfn); + rcu_read_unlock(); +} + +static void __init clear_early_alloc_pfn_tag_refs(void) +{ + unsigned int i; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_assign_pointer(alloc_tag_add_early_pfn_ptr, NULL); + /* Make sure we are not racing with __alloc_tag_add_early_pfn() */ + synchronize_rcu(); + + for (i = 0; i < atomic_read(&early_pfn_count); i++) { + unsigned long pfn = early_pfns[i]; + + if (pfn_valid(pfn)) { + struct page *page = pfn_to_page(pfn); + union pgtag_ref_handle handle; + union codetag_ref ref; + + if (get_page_tag_ref(page, &ref, &handle)) { + /* + * An early-allocated page could be freed and reallocated + * after its page_ext is initialized but before we clear it. + * In that case, it already has a valid tag set. + * We should not overwrite that valid tag with CODETAG_EMPTY. + * + * Note: there is still a small race window between checking + * ref.ct and calling set_codetag_empty(). We accept this + * race as it's unlikely and the extra complexity of atomic + * cmpxchg is not worth it for this debug-only code path. + */ + if (ref.ct) { + put_page_tag_ref(handle); + continue; + } + + set_codetag_empty(&ref); + update_page_tag_ref(handle, &ref); + put_page_tag_ref(handle); + } + } + + } +} +#else /* !CONFIG_MEM_ALLOC_PROFILING_DEBUG */ +static inline void __init clear_early_alloc_pfn_tag_refs(void) {} +#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */ + static __init void init_page_alloc_tagging(void) { + clear_early_alloc_pfn_tag_refs(); } struct page_ext_operations page_alloc_tagging_ops = {
mm/page_alloc.c+9 −2 modifieddiff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2d4b6f1a554ed..04494bc2e46f9 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1289,10 +1289,18 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task, union pgtag_ref_handle handle; union codetag_ref ref; - if (get_page_tag_ref(page, &ref, &handle)) { + if (likely(get_page_tag_ref(page, &ref, &handle))) { alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr); update_page_tag_ref(handle, &ref); put_page_tag_ref(handle); + } else { + /* + * page_ext is not available yet, record the pfn so we can + * clear the tag ref later when page_ext is initialized. + */ + alloc_tag_add_early_pfn(page_to_pfn(page)); + if (task->alloc_tag) + alloc_tag_set_inaccurate(task->alloc_tag); } } -- cgit 1.3-korg
6b1842775a46mm/alloc_tag: clear codetag for pages allocated before page_ext initialization
4 files changed · +121 −3
include/linux/alloc_tag.h+2 −0 modifieddiff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h index d40ac39bfbe8d..02de2ede560f3 100644 --- a/include/linux/alloc_tag.h +++ b/include/linux/alloc_tag.h @@ -163,9 +163,11 @@ static inline void alloc_tag_sub_check(union codetag_ref *ref) { WARN_ONCE(ref && !ref->ct, "alloc_tag was not set\n"); } +void alloc_tag_add_early_pfn(unsigned long pfn); #else static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag) {} static inline void alloc_tag_sub_check(union codetag_ref *ref) {} +static inline void alloc_tag_add_early_pfn(unsigned long pfn) {} #endif /* Caller should verify both ref and tag to be valid */
include/linux/pgalloc_tag.h+1 −1 modifieddiff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h index 38a82d65e58e9..951d333622685 100644 --- a/include/linux/pgalloc_tag.h +++ b/include/linux/pgalloc_tag.h @@ -181,7 +181,7 @@ static inline struct alloc_tag *__pgalloc_tag_get(struct page *page) if (get_page_tag_ref(page, &ref, &handle)) { alloc_tag_sub_check(&ref); - if (ref.ct) + if (ref.ct && !is_codetag_empty(&ref)) tag = ct_to_alloc_tag(ref.ct); put_page_tag_ref(handle); }
lib/alloc_tag.c+109 −0 modifieddiff --git a/lib/alloc_tag.c b/lib/alloc_tag.c index 58991ab09d84b..ed1bdcf1f8abf 100644 --- a/lib/alloc_tag.c +++ b/lib/alloc_tag.c @@ -6,7 +6,9 @@ #include <linux/kallsyms.h> #include <linux/module.h> #include <linux/page_ext.h> +#include <linux/pgalloc_tag.h> #include <linux/proc_fs.h> +#include <linux/rcupdate.h> #include <linux/seq_buf.h> #include <linux/seq_file.h> #include <linux/string_choices.h> @@ -758,8 +760,115 @@ static __init bool need_page_alloc_tagging(void) return mem_profiling_support; } +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG +/* + * Track page allocations before page_ext is initialized. + * Some pages are allocated before page_ext becomes available, leaving + * their codetag uninitialized. Track these early PFNs so we can clear + * their codetag refs later to avoid warnings when they are freed. + * + * Early allocations include: + * - Base allocations independent of CPU count + * - Per-CPU allocations (e.g., CPU hotplug callbacks during smp_init, + * such as trace ring buffers, scheduler per-cpu data) + * + * For simplicity, we fix the size to 8192. + * If insufficient, a warning will be triggered to alert the user. + * + * TODO: Replace fixed-size array with dynamic allocation using + * a GFP flag similar to ___GFP_NO_OBJ_EXT to avoid recursion. + */ +#define EARLY_ALLOC_PFN_MAX 8192 + +static unsigned long early_pfns[EARLY_ALLOC_PFN_MAX] __initdata; +static atomic_t early_pfn_count __initdata = ATOMIC_INIT(0); + +static void __init __alloc_tag_add_early_pfn(unsigned long pfn) +{ + int old_idx, new_idx; + + do { + old_idx = atomic_read(&early_pfn_count); + if (old_idx >= EARLY_ALLOC_PFN_MAX) { + pr_warn_once("Early page allocations before page_ext init exceeded EARLY_ALLOC_PFN_MAX (%d)\n", + EARLY_ALLOC_PFN_MAX); + return; + } + new_idx = old_idx + 1; + } while (!atomic_try_cmpxchg(&early_pfn_count, &old_idx, new_idx)); + + early_pfns[old_idx] = pfn; +} + +typedef void alloc_tag_add_func(unsigned long pfn); +static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata = + RCU_INITIALIZER(__alloc_tag_add_early_pfn); + +void alloc_tag_add_early_pfn(unsigned long pfn) +{ + alloc_tag_add_func *alloc_tag_add; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_read_lock(); + alloc_tag_add = rcu_dereference(alloc_tag_add_early_pfn_ptr); + if (alloc_tag_add) + alloc_tag_add(pfn); + rcu_read_unlock(); +} + +static void __init clear_early_alloc_pfn_tag_refs(void) +{ + unsigned int i; + + if (static_key_enabled(&mem_profiling_compressed)) + return; + + rcu_assign_pointer(alloc_tag_add_early_pfn_ptr, NULL); + /* Make sure we are not racing with __alloc_tag_add_early_pfn() */ + synchronize_rcu(); + + for (i = 0; i < atomic_read(&early_pfn_count); i++) { + unsigned long pfn = early_pfns[i]; + + if (pfn_valid(pfn)) { + struct page *page = pfn_to_page(pfn); + union pgtag_ref_handle handle; + union codetag_ref ref; + + if (get_page_tag_ref(page, &ref, &handle)) { + /* + * An early-allocated page could be freed and reallocated + * after its page_ext is initialized but before we clear it. + * In that case, it already has a valid tag set. + * We should not overwrite that valid tag with CODETAG_EMPTY. + * + * Note: there is still a small race window between checking + * ref.ct and calling set_codetag_empty(). We accept this + * race as it's unlikely and the extra complexity of atomic + * cmpxchg is not worth it for this debug-only code path. + */ + if (ref.ct) { + put_page_tag_ref(handle); + continue; + } + + set_codetag_empty(&ref); + update_page_tag_ref(handle, &ref); + put_page_tag_ref(handle); + } + } + + } +} +#else /* !CONFIG_MEM_ALLOC_PROFILING_DEBUG */ +static inline void __init clear_early_alloc_pfn_tag_refs(void) {} +#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */ + static __init void init_page_alloc_tagging(void) { + clear_early_alloc_pfn_tag_refs(); } struct page_ext_operations page_alloc_tagging_ops = {
mm/page_alloc.c+9 −2 modifieddiff --git a/mm/page_alloc.c b/mm/page_alloc.c index 111b54df8a3cb..b1c5430cad4e5 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1252,10 +1252,18 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task, union pgtag_ref_handle handle; union codetag_ref ref; - if (get_page_tag_ref(page, &ref, &handle)) { + if (likely(get_page_tag_ref(page, &ref, &handle))) { alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr); update_page_tag_ref(handle, &ref); put_page_tag_ref(handle); + } else { + /* + * page_ext is not available yet, record the pfn so we can + * clear the tag ref later when page_ext is initialized. + */ + alloc_tag_add_early_pfn(page_to_pfn(page)); + if (task->alloc_tag) + alloc_tag_set_inaccurate(task->alloc_tag); } } -- cgit 1.3-korg
Vulnerability mechanics
Root cause
"Pages allocated before page_ext initialization lack a codetag, leading to warnings when reclaimed."
Attack vector
This issue occurs during system boot when pages are allocated before the page_ext subsystem is fully initialized. Specifically, when `alloc_page_ext()` calls `kmemleak_alloc()` and the slab cache has no free objects, it falls back to the buddy allocator. The newly allocated pages lack a codetag because `page_ext` is not yet ready. These pages can later be reclaimed by KASAN, triggering a warning upon freeing due to the uninitialized codetag.
Affected code
The vulnerability lies within the memory allocation path in `mm/page_alloc.c`, specifically in the `__pgalloc_tag_add` function. The fix involves modifications in `lib/alloc_tag.c` and `include/linux/alloc_tag.h` to introduce tracking for early page allocations.
What the fix does
The patch introduces a global array `early_pfns` to track pages allocated before `page_ext` initialization. When such a page is encountered, its PFN is recorded. After `page_ext` is fully initialized, the `clear_early_alloc_pfn_tag_refs()` function iterates through the recorded PFNs and sets their codetags to empty. This prevents the KASAN warning from triggering when these pages are later freed.
Preconditions
- configCONFIG_MEM_ALLOC_PROFILING_DEBUG=Y must be enabled.
- configmem_profiling_compressed must be disabled.
Generated on Jun 8, 2026. Inputs: CWE entries + fix-commit diffs from this CVE's patches. Citations validated against bundle.
References
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