[PATCH v4] mm,kfence: decouple kfence from page granularity mapping judgement

[PATCH v4] 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, arm64_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@arm.com>
Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
---
 arch/arm64/mm/mmu.c      | 42 ++++++++++++++++++++++++++++++++++++++++++
 arch/arm64/mm/pageattr.c |  5 ++---
 include/linux/kfence.h   |  8 ++++++++
 mm/kfence/core.c         |  9 +++++++++
 4 files changed, 61 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 6f9d889..ca5c932 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>
@@ -525,6 +526,31 @@ static int __init enable_crash_mem_map(char *arg)
 }
 early_param("crashkernel", enable_crash_mem_map);
 
+#ifdef CONFIG_KFENCE
+
+static phys_addr_t arm64_kfence_alloc_pool(void)
+{
+	phys_addr_t kfence_pool;
+
+	if (!kfence_sample_interval)
+		return 0;
+
+	kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
+	if (!kfence_pool)
+		pr_err("failed to allocate kfence pool\n");
+
+	return kfence_pool;
+}
+
+#else
+
+static phys_addr_t arm64_kfence_alloc_pool(void)
+{
+	return 0;
+}
+
+#endif
+
 static void __init map_mem(pgd_t *pgdp)
 {
 	static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
@@ -532,6 +558,7 @@ 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;
+	phys_addr_t kfence_pool;
 	u64 i;
 
 	/*
@@ -564,6 +591,10 @@ static void __init map_mem(pgd_t *pgdp)
 	}
 #endif
 
+	kfence_pool = arm64_kfence_alloc_pool();
+	if (kfence_pool)
+		memblock_mark_nomap(kfence_pool, KFENCE_POOL_SIZE);
+
 	/* map all the memory banks */
 	for_each_mem_range(i, &start, &end) {
 		if (start >= end)
@@ -608,6 +639,17 @@ static void __init map_mem(pgd_t *pgdp)
 		}
 	}
 #endif
+
+	/* Kfence pool needs page-level mapping */
+	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);
+	}
 }
 
 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..570d4e3 100644
--- a/include/linux/kfence.h
+++ b/include/linux/kfence.h
@@ -64,6 +64,12 @@ static __always_inline bool is_kfence_address(const void *addr)
 void __init kfence_alloc_pool(void);
 
 /**
+ * kfence_set_pool() - allows an arch to set the
+ * KFENCE pool during early init
+ */
+void __init kfence_set_pool(phys_addr_t addr);
+
+/**
  * kfence_init() - perform KFENCE initialization at boot time
  *
  * Requires that kfence_alloc_pool() was called before. This sets up the
@@ -222,8 +228,10 @@ bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *sla
 
 #else /* CONFIG_KFENCE */
 
+#define KFENCE_POOL_SIZE 0
 static inline bool is_kfence_address(const void *addr) { return false; }
 static inline void kfence_alloc_pool(void) { }
+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/mm/kfence/core.c b/mm/kfence/core.c
index 5349c37..0765395 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -814,12 +814,21 @@ void __init kfence_alloc_pool(void)
 	if (!kfence_sample_interval)
 		return;
 
+	/* if the pool has already been initialized by arch, skip the below */
+	if (__kfence_pool)
+		return;
+
 	__kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
 
 	if (!__kfence_pool)
 		pr_err("failed to allocate pool\n");
 }
 
+void __init kfence_set_pool(phys_addr_t addr)
+{
+	__kfence_pool = phys_to_virt(addr);
+}
+
 static void kfence_init_enable(void)
 {
 	if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS))
-- 
2.7.4

Re: [PATCH v4] mm,kfence: decouple kfence from page granularity mapping judgement

[Andrew Morton]

On Fri, 10 Mar 2023 17:30:04 +0800 Zhenhua Huang <quic_zhenhuah@quicinc.com> wrote:

> 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, arm64_kfence_alloc_pool is to allocate phys
> addr, __kfence_pool is to be set after linear mapping set up.

Why make this change?  What are the benefits?  What are the user
visible effects?

> LINK: [1] https://lore.kernel.org/linux-arm-kernel/1675750519-1064-1-git-send-email-quic_zhenhuah@quicinc.com/T/

Chasing the links indicates that "page-granular mapping costed more (2M
per 1GB) memory".  Please spell all this out in this patch's changelog.

btw. this format:

Link: https://lore.kernel.org/linux-arm-kernel/1675750519-1064-1-git-send-email-quic_zhenhuah@quicinc.com/T/ [1]

is conventional.

Re: [PATCH v4] mm,kfence: decouple kfence from page granularity mapping judgement

[Zhenhua Huang]

Thanks Andrew!

On 2023/3/13 5:01, Andrew Morton wrote:
> On Fri, 10 Mar 2023 17:30:04 +0800 Zhenhua Huang <quic_zhenhuah@quicinc.com> wrote:
> 
>> 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, arm64_kfence_alloc_pool is to allocate phys
>> addr, __kfence_pool is to be set after linear mapping set up.
> 
> Why make this change?  What are the benefits?  What are the user
> visible effects?
> 
>> LINK: [1] https://lore.kernel.org/linux-arm-kernel/1675750519-1064-1-git-send-email-quic_zhenhuah@quicinc.com/T/
> 
> Chasing the links indicates that "page-granular mapping costed more (2M
> per 1GB) memory".  Please spell all this out in this patch's changelog.

Yeah, let me update these and also my test outcome in changelog to make 
it clear~! Thanks.

> 
> btw. this format:
> 
> Link: https://lore.kernel.org/linux-arm-kernel/1675750519-1064-1-git-send-email-quic_zhenhuah@quicinc.com/T/ [1]
> 
> is conventional.

Do you mean it was not directly pointing to Mark's suggestion? let me 
update to: 
https://lore.kernel.org/linux-arm-kernel/Y+IsdrvDNILA59UN@FVFF77S0Q05N/

>