On 2023/3/14 16:41, Marco Elver wrote:
On Tue, 14 Mar 2023 at 08:05, Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx> wrote:
Kfence only needs its pool to be mapped as page granularity, if it is
inited early. Previous judgement was a bit over protected. From [1], Mark
suggested to "just map the KFENCE region a page granularity". So I
decouple it from judgement and do page granularity mapping for kfence
pool only. Need to be noticed that late init of kfence pool still requires
page granularity mapping.
Page granularity mapping in theory cost more(2M per 1GB) memory on arm64
platform. Like what I've tested on QEMU(emulated 1GB RAM) with
gki_defconfig, also turning off rodata protection:
Before:
[root@liebao ]# cat /proc/meminfo
MemTotal: 999484 kB
After:
[root@liebao ]# cat /proc/meminfo
MemTotal: 1001480 kB
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/Y+IsdrvDNILA59UN@FVFF77S0Q05N/
Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx>
---
arch/arm64/include/asm/kfence.h | 2 ++
arch/arm64/mm/mmu.c | 44 +++++++++++++++++++++++++++++++++++++++++
arch/arm64/mm/pageattr.c | 9 +++++++--
include/linux/kfence.h | 8 ++++++++
mm/kfence/core.c | 9 +++++++++
5 files changed, 70 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h
index aa855c6..f1f9ca2d 100644
--- a/arch/arm64/include/asm/kfence.h
+++ b/arch/arm64/include/asm/kfence.h
@@ -10,6 +10,8 @@
#include <asm/set_memory.h>
+extern phys_addr_t early_kfence_pool;
+
static inline bool arch_kfence_init_pool(void) { return true; }
static inline bool kfence_protect_page(unsigned long addr, bool protect)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 6f9d889..7fbf2ed 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>
@@ -38,6 +39,7 @@
#include <asm/ptdump.h>
#include <asm/tlbflush.h>
#include <asm/pgalloc.h>
+#include <asm/kfence.h>
#define NO_BLOCK_MAPPINGS BIT(0)
#define NO_CONT_MAPPINGS BIT(1)
@@ -525,6 +527,33 @@ 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
+
+phys_addr_t early_kfence_pool;
The compiler will not optimize out this global. This now exists in all
arm64 kernel builds.
Furthermore, there's no need for this to be phys_addr_t. Nothing
outside map_mem() needs the address, so this can just be a bool.
Seems we need this early_kfence_bool to be explicit phys_addr_t as we
need to mark/clear NOMAP for the region, so that it will not do linear
mapping in the for loop.
I'd recommend moving the variable under CONFIG_KFENCE, and in the asm
header, just having a static inline helper function e.g.
arm64_kfence_early_pool(). That helper just returns false in the
!CONFIG_KFENCE case.
static void __init map_mem(pgd_t *pgdp)
{
static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
@@ -543,6 +572,10 @@ static void __init map_mem(pgd_t *pgdp)
*/
BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end));
+ early_kfence_pool = arm64_kfence_alloc_pool();
+ if (early_kfence_pool)
+ memblock_mark_nomap(early_kfence_pool, KFENCE_POOL_SIZE);
+
if (can_set_direct_map())
flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
@@ -608,6 +641,17 @@ static void __init map_mem(pgd_t *pgdp)
}
}
#endif
+
+ /* Kfence pool needs page-level mapping */
+ if (early_kfence_pool) {
+ __map_memblock(pgdp, early_kfence_pool,
+ early_kfence_pool + KFENCE_POOL_SIZE,
+ pgprot_tagged(PAGE_KERNEL),
+ NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
+ memblock_clear_nomap(early_kfence_pool, KFENCE_POOL_SIZE);
+ /* kfence_pool really mapped now */
+ kfence_set_pool(early_kfence_pool);
+ }
}
void mark_rodata_ro(void)
diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
index 79dd201..7ce5295 100644
--- a/arch/arm64/mm/pageattr.c
+++ b/arch/arm64/mm/pageattr.c
@@ -7,10 +7,12 @@
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/vmalloc.h>
+#include <linux/kfence.h>
#include <asm/cacheflush.h>
#include <asm/set_memory.h>
#include <asm/tlbflush.h>
+#include <asm/kfence.h>
struct page_change_data {
pgprot_t set_mask;
@@ -22,12 +24,15 @@ 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.
+ *
+ * Kfence pool requires page granularity mapping also if we init it
+ * late.
*/
return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
- IS_ENABLED(CONFIG_KFENCE);
+ (IS_ENABLED(CONFIG_KFENCE) && !early_kfence_pool);
}
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);
+}
Please move this function to the header as a static inline function,
because nothing else other than arm64 needs this, having this function
be here introduces a .text size increase for everyone.
The function is so short that having it as a static inline function is
fine, and will save a few bytes of .text.
Reasonable! Thanks!
static void kfence_init_enable(void)
{
if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS))
--
2.7.4
Thanks,
Zhenhua
