[PATCH v7] mm,kfence: decouple kfence from page granularity mapping judgement
Zhenhua Huang
quic_zhenhuah at quicinc.com
Mon Mar 13 23:35:15 PDT 2023
On 2023/3/14 13:26, Zhenhua Huang 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 at liebao ]# cat /proc/meminfo
> MemTotal: 999484 kB
> After:
> [root at 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 at arm.com>
> Signed-off-by: Zhenhua Huang <quic_zhenhuah at quicinc.com>
> ---
> arch/arm64/mm/mmu.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> arch/arm64/mm/pageattr.c | 8 ++++++--
> include/linux/kfence.h | 11 +++++++++++
> mm/kfence/core.c | 9 +++++++++
> 4 files changed, 69 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 6f9d889..7f34206 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 +526,33 @@ 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;
I suddenly realized it would break other arch as only defined under
arm64, let me relocate the declaration to arm64 headers as well. Sorry
for inconvenience.
> +
> static void __init map_mem(pgd_t *pgdp)
> {
> static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
> @@ -543,6 +571,10 @@ 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 +640,17 @@ 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..83f57d2 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -7,6 +7,7 @@
> #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>
> @@ -22,12 +23,15 @@ 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..f1330b6 100644
> --- a/include/linux/kfence.h
> +++ b/include/linux/kfence.h
> @@ -18,6 +18,7 @@
> #include <linux/static_key.h>
>
> extern unsigned long kfence_sample_interval;
> +extern phys_addr_t early_kfence_pool;
>
> /*
> * We allocate an even number of pages, as it simplifies calculations to map
> @@ -64,6 +65,12 @@ 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 +229,12 @@ bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *sla
>
> #else /* CONFIG_KFENCE */
>
> +extern phys_addr_t early_kfence_pool;
> +
> +#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))
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