Re: [PATCH v10] mm,kfence: decouple kfence from page granularity mapping judgement

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2023/3/16 20:18, 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@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.
> 

A few little comments,


> LINK: [1] https://lore.kernel.org/linux-arm-kernel/Y+IsdrvDNILA59UN@FVFF77S0Q05N/
> Suggested-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Zhenhua Huang <quic_zhenhuah@quicinc.com>
> ---
>   arch/arm64/include/asm/kfence.h | 10 +++++++
>   arch/arm64/mm/mmu.c             | 61 +++++++++++++++++++++++++++++++++++++++++
>   arch/arm64/mm/pageattr.c        |  7 +++--
>   mm/kfence/core.c                |  4 +++
>   4 files changed, 80 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h
> index aa855c6..a81937f 100644
> --- a/arch/arm64/include/asm/kfence.h
> +++ b/arch/arm64/include/asm/kfence.h
> @@ -19,4 +19,14 @@ static inline bool kfence_protect_page(unsigned long addr, bool protect)
>   	return true;
>   }
>   
> +#ifdef CONFIG_KFENCE
> +extern bool kfence_early_init;
> +static inline bool arm64_kfence_can_set_direct_map(void)
> +{
> +	return !kfence_early_init;
> +}
> +#else /* CONFIG_KFENCE */
> +static inline bool arm64_kfence_can_set_direct_map(void) { return false; }
> +#endif /* CONFIG_KFENCE */
> +
>   #endif /* __ASM_KFENCE_H */
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index ae25524d..aaf1801 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)
> @@ -521,12 +523,67 @@ static int __init enable_crash_mem_map(char *arg)
>   }
>   early_param("crashkernel", enable_crash_mem_map);
>   
> +#ifdef CONFIG_KFENCE
> +
> +bool kfence_early_init = !!CONFIG_KFENCE_SAMPLE_INTERVAL;

maybe add __ro_after_init

> +
> +/* early_param() will be parsed before map_mem() below. */
> +static int __init parse_kfence_early_init(char *arg)
> +{
> +	int val;
> +
> +	if (get_option(&arg, &val))
> +		kfence_early_init = !!val;
> +	return 0;
> +}
> +early_param("kfence.sample_interval", parse_kfence_early_init);
> +
> +static phys_addr_t arm64_kfence_alloc_pool(void)

and __init

> +{
> +	phys_addr_t kfence_pool;
> +
> +	if (!kfence_early_init)
> +		return 0;
> +
> +	kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
> +	if (!kfence_pool) {
> +		pr_err("failed to allocate kfence pool\n");
> +		kfence_early_init = false;
> +		return 0;
> +	}
> +
> +	/* Temporarily mark as NOMAP. */
> +	memblock_mark_nomap(kfence_pool, KFENCE_POOL_SIZE);
> +
> +	return kfence_pool;
> +}
> +
> +static void arm64_kfence_map_pool(phys_addr_t kfence_pool, pgd_t *pgdp)

Ditto.

Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>

> +{
> +	if (!kfence_pool)
> +		return;
> +
> +	/* KFENCE pool needs page-level mapping. */
> +	__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 = phys_to_virt(kfence_pool);
> +}
> +#else /* CONFIG_KFENCE */
> +
> +static inline phys_addr_t arm64_kfence_alloc_pool(void) { return 0; }
> +static inline void arm64_kfence_map_pool(phys_addr_t kfence_pool, pgd_t *pgdp) { }
> +
> +#endif /* CONFIG_KFENCE */
> +
>   static void __init map_mem(pgd_t *pgdp)
>   {
>   	static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
>   	phys_addr_t kernel_start = __pa_symbol(_stext);
>   	phys_addr_t kernel_end = __pa_symbol(__init_begin);
>   	phys_addr_t start, end;
> +	phys_addr_t early_kfence_pool;
>   	int flags = NO_EXEC_MAPPINGS;
>   	u64 i;
>   
> @@ -539,6 +596,8 @@ 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 (can_set_direct_map())
>   		flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>   
> @@ -604,6 +663,8 @@ static void __init map_mem(pgd_t *pgdp)
>   		}
>   	}
>   #endif
> +
> +	arm64_kfence_map_pool(early_kfence_pool, pgdp);
>   }
>   
>   void mark_rodata_ro(void)
> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
> index debdecf..dd1291a 100644
> --- a/arch/arm64/mm/pageattr.c
> +++ b/arch/arm64/mm/pageattr.c
> @@ -11,6 +11,7 @@
>   #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 +23,14 @@ 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-granular mapping if initialized late.
>   	 */
>   	return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
> -		IS_ENABLED(CONFIG_KFENCE);
> +		arm64_kfence_can_set_direct_map();
>   }
>   
>   static int change_page_range(pte_t *ptep, unsigned long addr, void *data)
> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
> index 1417888..bf2f194c 100644
> --- a/mm/kfence/core.c
> +++ b/mm/kfence/core.c
> @@ -824,6 +824,10 @@ 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)