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

[Zhenhua Huang <quic_zhenhuah@quicinc.com>]

On 2023/3/16 22:15, Kefeng Wang wrote:
> 
> 
> 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,

Thanks Kefeng. Addressed your comments in latest patch.

Thanks,
Zhenhua

> 
> 
>> 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)