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Message-ID: <176762845862.510.9590247050620583118.tip-bot2@tip-bot2>
Date: Mon, 05 Jan 2026 15:54:18 -0000
From: "tip-bot2 for Marco Elver" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Marco Elver <elver@...gle.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: locking/core] kfence: Enable context analysis
The following commit has been merged into the locking/core branch of tip:
Commit-ID: 0f5d764862aa7f50d77b8ea2b4f75a48a630487a
Gitweb: https://git.kernel.org/tip/0f5d764862aa7f50d77b8ea2b4f75a48a630487a
Author: Marco Elver <elver@...gle.com>
AuthorDate: Fri, 19 Dec 2025 16:40:17 +01:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 05 Jan 2026 16:43:34 +01:00
kfence: Enable context analysis
Enable context analysis for the KFENCE subsystem.
Notable, kfence_handle_page_fault() required minor restructure, which
also fixed a subtle race; arguably that function is more readable now.
Signed-off-by: Marco Elver <elver@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://patch.msgid.link/20251219154418.3592607-29-elver@google.com
---
mm/kfence/Makefile | 2 ++
mm/kfence/core.c | 20 +++++++++++++-------
mm/kfence/kfence.h | 14 ++++++++------
mm/kfence/report.c | 4 ++--
4 files changed, 25 insertions(+), 15 deletions(-)
diff --git a/mm/kfence/Makefile b/mm/kfence/Makefile
index 2de2a58..a503e83 100644
--- a/mm/kfence/Makefile
+++ b/mm/kfence/Makefile
@@ -1,5 +1,7 @@
# SPDX-License-Identifier: GPL-2.0
+CONTEXT_ANALYSIS := y
+
obj-y := core.o report.o
CFLAGS_kfence_test.o := -fno-omit-frame-pointer -fno-optimize-sibling-calls
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 577a169..ebf442f 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -133,8 +133,8 @@ struct kfence_metadata *kfence_metadata __read_mostly;
static struct kfence_metadata *kfence_metadata_init __read_mostly;
/* Freelist with available objects. */
-static struct list_head kfence_freelist = LIST_HEAD_INIT(kfence_freelist);
-static DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */
+DEFINE_RAW_SPINLOCK(kfence_freelist_lock); /* Lock protecting freelist. */
+static struct list_head kfence_freelist __guarded_by(&kfence_freelist_lock) = LIST_HEAD_INIT(kfence_freelist);
/*
* The static key to set up a KFENCE allocation; or if static keys are not used
@@ -254,6 +254,7 @@ static bool kfence_unprotect(unsigned long addr)
}
static inline unsigned long metadata_to_pageaddr(const struct kfence_metadata *meta)
+ __must_hold(&meta->lock)
{
unsigned long offset = (meta - kfence_metadata + 1) * PAGE_SIZE * 2;
unsigned long pageaddr = (unsigned long)&__kfence_pool[offset];
@@ -289,6 +290,7 @@ static inline bool kfence_obj_allocated(const struct kfence_metadata *meta)
static noinline void
metadata_update_state(struct kfence_metadata *meta, enum kfence_object_state next,
unsigned long *stack_entries, size_t num_stack_entries)
+ __must_hold(&meta->lock)
{
struct kfence_track *track =
next == KFENCE_OBJECT_ALLOCATED ? &meta->alloc_track : &meta->free_track;
@@ -486,7 +488,7 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g
alloc_covered_add(alloc_stack_hash, 1);
/* Set required slab fields. */
- slab = virt_to_slab((void *)meta->addr);
+ slab = virt_to_slab(addr);
slab->slab_cache = cache;
slab->objects = 1;
@@ -515,6 +517,7 @@ static void *kfence_guarded_alloc(struct kmem_cache *cache, size_t size, gfp_t g
static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool zombie)
{
struct kcsan_scoped_access assert_page_exclusive;
+ u32 alloc_stack_hash;
unsigned long flags;
bool init;
@@ -547,9 +550,10 @@ static void kfence_guarded_free(void *addr, struct kfence_metadata *meta, bool z
/* Mark the object as freed. */
metadata_update_state(meta, KFENCE_OBJECT_FREED, NULL, 0);
init = slab_want_init_on_free(meta->cache);
+ alloc_stack_hash = meta->alloc_stack_hash;
raw_spin_unlock_irqrestore(&meta->lock, flags);
- alloc_covered_add(meta->alloc_stack_hash, -1);
+ alloc_covered_add(alloc_stack_hash, -1);
/* Check canary bytes for memory corruption. */
check_canary(meta);
@@ -594,6 +598,7 @@ static void rcu_guarded_free(struct rcu_head *h)
* which partial initialization succeeded.
*/
static unsigned long kfence_init_pool(void)
+ __context_unsafe(/* constructor */)
{
unsigned long addr, start_pfn;
int i;
@@ -1220,6 +1225,7 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
{
const int page_index = (addr - (unsigned long)__kfence_pool) / PAGE_SIZE;
struct kfence_metadata *to_report = NULL;
+ unsigned long unprotected_page = 0;
enum kfence_error_type error_type;
unsigned long flags;
@@ -1253,9 +1259,8 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
if (!to_report)
goto out;
- raw_spin_lock_irqsave(&to_report->lock, flags);
- to_report->unprotected_page = addr;
error_type = KFENCE_ERROR_OOB;
+ unprotected_page = addr;
/*
* If the object was freed before we took the look we can still
@@ -1267,7 +1272,6 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
if (!to_report)
goto out;
- raw_spin_lock_irqsave(&to_report->lock, flags);
error_type = KFENCE_ERROR_UAF;
/*
* We may race with __kfence_alloc(), and it is possible that a
@@ -1279,6 +1283,8 @@ bool kfence_handle_page_fault(unsigned long addr, bool is_write, struct pt_regs
out:
if (to_report) {
+ raw_spin_lock_irqsave(&to_report->lock, flags);
+ to_report->unprotected_page = unprotected_page;
kfence_report_error(addr, is_write, regs, to_report, error_type);
raw_spin_unlock_irqrestore(&to_report->lock, flags);
} else {
diff --git a/mm/kfence/kfence.h b/mm/kfence/kfence.h
index dfba5ea..f9caea0 100644
--- a/mm/kfence/kfence.h
+++ b/mm/kfence/kfence.h
@@ -34,6 +34,8 @@
/* Maximum stack depth for reports. */
#define KFENCE_STACK_DEPTH 64
+extern raw_spinlock_t kfence_freelist_lock;
+
/* KFENCE object states. */
enum kfence_object_state {
KFENCE_OBJECT_UNUSED, /* Object is unused. */
@@ -53,7 +55,7 @@ struct kfence_track {
/* KFENCE metadata per guarded allocation. */
struct kfence_metadata {
- struct list_head list; /* Freelist node; access under kfence_freelist_lock. */
+ struct list_head list __guarded_by(&kfence_freelist_lock); /* Freelist node. */
struct rcu_head rcu_head; /* For delayed freeing. */
/*
@@ -91,13 +93,13 @@ struct kfence_metadata {
* In case of an invalid access, the page that was unprotected; we
* optimistically only store one address.
*/
- unsigned long unprotected_page;
+ unsigned long unprotected_page __guarded_by(&lock);
/* Allocation and free stack information. */
- struct kfence_track alloc_track;
- struct kfence_track free_track;
+ struct kfence_track alloc_track __guarded_by(&lock);
+ struct kfence_track free_track __guarded_by(&lock);
/* For updating alloc_covered on frees. */
- u32 alloc_stack_hash;
+ u32 alloc_stack_hash __guarded_by(&lock);
#ifdef CONFIG_MEMCG
struct slabobj_ext obj_exts;
#endif
@@ -141,6 +143,6 @@ enum kfence_error_type {
void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *regs,
const struct kfence_metadata *meta, enum kfence_error_type type);
-void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta);
+void kfence_print_object(struct seq_file *seq, const struct kfence_metadata *meta) __must_hold(&meta->lock);
#endif /* MM_KFENCE_KFENCE_H */
diff --git a/mm/kfence/report.c b/mm/kfence/report.c
index 10e6802..787e87c 100644
--- a/mm/kfence/report.c
+++ b/mm/kfence/report.c
@@ -106,6 +106,7 @@ found:
static void kfence_print_stack(struct seq_file *seq, const struct kfence_metadata *meta,
bool show_alloc)
+ __must_hold(&meta->lock)
{
const struct kfence_track *track = show_alloc ? &meta->alloc_track : &meta->free_track;
u64 ts_sec = track->ts_nsec;
@@ -207,8 +208,6 @@ void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *r
if (WARN_ON(type != KFENCE_ERROR_INVALID && !meta))
return;
- if (meta)
- lockdep_assert_held(&meta->lock);
/*
* Because we may generate reports in printk-unfriendly parts of the
* kernel, such as scheduler code, the use of printk() could deadlock.
@@ -263,6 +262,7 @@ void kfence_report_error(unsigned long address, bool is_write, struct pt_regs *r
stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, 0);
if (meta) {
+ lockdep_assert_held(&meta->lock);
pr_err("\n");
kfence_print_object(NULL, meta);
}
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