[PATCH] mm,kfence: decouple kfence from page granularity mapping judgement

[Zhenhua Huang]

Kfence only needs its pool to be mapped as page granularity, previous
judgement was a bit over protected. Decouple it from judgement and do
page granularity mapping for kfence pool only [1].

To implement this, also relocate the kfence pool allocation before the
linear mapping setting up, kfence_alloc_pool is to allocate phys addr,
__kfence_pool is to be set after linear mapping set up.

LINK: [1] https://lore.kernel.org/linux-arm-kernel/1675750519-1064-1-git-send-email-quic_zhenhuah@quicinc.com/T/
Suggested-by: Mark Rutland <mark.rutland at arm.com>
Signed-off-by: Zhenhua Huang <quic_zhenhuah at quicinc.com>
---
 arch/arm64/mm/mmu.c      | 24 ++++++++++++++++++++++++
 arch/arm64/mm/pageattr.c |  5 ++---
 include/linux/kfence.h   | 10 ++++++++--
 init/main.c              |  1 -
 mm/kfence/core.c         | 18 ++++++++++++++----
 5 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 6f9d889..bd79691 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -24,6 +24,7 @@
 #include <linux/mm.h>
 #include <linux/vmalloc.h>
 #include <linux/set_memory.h>
+#include <linux/kfence.h>
 
 #include <asm/barrier.h>
 #include <asm/cputype.h>
@@ -532,6 +533,9 @@ static void __init map_mem(pgd_t *pgdp)
 	phys_addr_t kernel_end = __pa_symbol(__init_begin);
 	phys_addr_t start, end;
 	int flags = NO_EXEC_MAPPINGS;
+#ifdef CONFIG_KFENCE
+	phys_addr_t kfence_pool = 0;
+#endif
 	u64 i;
 
 	/*
@@ -564,6 +568,12 @@ static void __init map_mem(pgd_t *pgdp)
 	}
 #endif
 
+#ifdef CONFIG_KFENCE
+	kfence_pool = kfence_alloc_pool();
+	if (kfence_pool)
+		memblock_mark_nomap(kfence_pool, KFENCE_POOL_SIZE);
+#endif
+
 	/* map all the memory banks */
 	for_each_mem_range(i, &start, &end) {
 		if (start >= end)
@@ -608,6 +618,20 @@ static void __init map_mem(pgd_t *pgdp)
 		}
 	}
 #endif
+
+	/* Kfence pool needs page-level mapping */
+#ifdef CONFIG_KFENCE
+	if (kfence_pool) {
+		__map_memblock(pgdp, kfence_pool,
+			kfence_pool + KFENCE_POOL_SIZE,
+			pgprot_tagged(PAGE_KERNEL),
+			NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
+		memblock_clear_nomap(kfence_pool, KFENCE_POOL_SIZE);
+		/* kfence_pool really mapped now */
+		kfence_set_pool(kfence_pool);
+	}
+#endif
+
 }
 
 void mark_rodata_ro(void)
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 79dd201..61156d0 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -22,12 +22,11 @@ bool rodata_full __ro_after_init = IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED
 bool can_set_direct_map(void)
 {
 	/*
-	 * rodata_full, DEBUG_PAGEALLOC and KFENCE require linear map to be
+	 * rodata_full and DEBUG_PAGEALLOC require linear map to be
 	 * mapped at page granularity, so that it is possible to
 	 * protect/unprotect single pages.
 	 */
-	return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
-		IS_ENABLED(CONFIG_KFENCE);
+	return (rodata_enabled && rodata_full) || debug_pagealloc_enabled();
 }
 
 static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
diff --git a/include/linux/kfence.h b/include/linux/kfence.h
index 726857a..0252e74 100644
--- a/include/linux/kfence.h
+++ b/include/linux/kfence.h
@@ -61,7 +61,12 @@ static __always_inline bool is_kfence_address(const void *addr)
 /**
  * kfence_alloc_pool() - allocate the KFENCE pool via memblock
  */
-void __init kfence_alloc_pool(void);
+phys_addr_t __init kfence_alloc_pool(void);
+
+/**
+ * kfence_set_pool() - KFENCE pool mapped and can be used
+ */
+void __init kfence_set_pool(phys_addr_t addr);
 
 /**
  * kfence_init() - perform KFENCE initialization at boot time
@@ -223,7 +228,8 @@ bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *sla
 #else /* CONFIG_KFENCE */
 
 static inline bool is_kfence_address(const void *addr) { return false; }
-static inline void kfence_alloc_pool(void) { }
+static inline phys_addr_t kfence_alloc_pool(void) { return (phys_addr_t)NULL; }
+static inline void kfence_set_pool(phys_addr_t addr) { }
 static inline void kfence_init(void) { }
 static inline void kfence_shutdown_cache(struct kmem_cache *s) { }
 static inline void *kfence_alloc(struct kmem_cache *s, size_t size, gfp_t flags) { return NULL; }
diff --git a/init/main.c b/init/main.c
index 4425d17..9aaf217 100644
--- a/init/main.c
+++ b/init/main.c
@@ -839,7 +839,6 @@ static void __init mm_init(void)
 	 */
 	page_ext_init_flatmem();
 	init_mem_debugging_and_hardening();
-	kfence_alloc_pool();
 	report_meminit();
 	kmsan_init_shadow();
 	stack_depot_early_init();
diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 5349c37..dd5cdd5 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -809,15 +809,25 @@ static void toggle_allocation_gate(struct work_struct *work)
 
 /* === Public interface ===================================================== */
 
-void __init kfence_alloc_pool(void)
+phys_addr_t __init kfence_alloc_pool(void)
 {
+	phys_addr_t kfence_pool;
 	if (!kfence_sample_interval)
-		return;
+		return 0;
 
-	__kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
+	kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
 
-	if (!__kfence_pool)
+	if (!kfence_pool) {
 		pr_err("failed to allocate pool\n");
+		return 0;
+	}
+
+	return kfence_pool;
+}
+
+void __init kfence_set_pool(phys_addr_t addr)
+{
+	__kfence_pool = phys_to_virt(addr);
 }
 
 static void kfence_init_enable(void)
-- 
2.7.4