[PATCH v9] mm,kfence: decouple kfence from page granularity mapping judgement

[Pavan Kondeti]

On Thu, Mar 16, 2023 at 04:50:20PM +0800, 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/include/asm/kfence.h | 16 +++++++++++
>  arch/arm64/mm/mmu.c             | 59 +++++++++++++++++++++++++++++++++++++++++
>  arch/arm64/mm/pageattr.c        |  9 +++++--
>  include/linux/kfence.h          |  1 +
>  mm/kfence/core.c                |  4 +++
>  5 files changed, 87 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h
> index aa855c6..8143c91 100644
> --- a/arch/arm64/include/asm/kfence.h
> +++ b/arch/arm64/include/asm/kfence.h
> @@ -10,6 +10,22 @@
>  
>  #include <asm/set_memory.h>
>  
> +extern phys_addr_t early_kfence_pool;
> +
> +#ifdef CONFIG_KFENCE
> +
> +extern char *__kfence_pool;
> +static inline void kfence_set_pool(phys_addr_t addr)
> +{
> +	__kfence_pool = phys_to_virt(addr);
> +}
> +
> +#else
> +
> +static inline void kfence_set_pool(phys_addr_t addr) { }
> +
> +#endif
> +
>  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..61944c70 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 +527,48 @@ static int __init enable_crash_mem_map(char *arg)
>  }
>  early_param("crashkernel", enable_crash_mem_map);
>  
> +#ifdef CONFIG_KFENCE
> +
> +static bool kfence_early_init __initdata = !!CONFIG_KFENCE_SAMPLE_INTERVAL;
> +/*
> + * early_param can be parsed before linear mapping
> + * set up
> + */
> +static int __init parse_kfence_early_init(char *p)
> +{
> +	int val;
> +
> +	if (get_option(&p, &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)
> +{
> +	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");
> +
> +	return kfence_pool;
> +}
> +
> +#else
> +
> +static phys_addr_t arm64_kfence_alloc_pool(void)
> +{
> +	return 0;
> +}
> +
> +#endif
> +
> +phys_addr_t early_kfence_pool;
> +
>  static void __init map_mem(pgd_t *pgdp)
>  {
>  	static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
> @@ -543,6 +587,10 @@ 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 +656,17 @@ 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);
> +	}

Why not wrap this under CONFIG_KFENCE ? early_kfence_pool can also go in
there?

Thanks,
Pavan