[PATCH v9] mm,kfence: decouple kfence from page granularity mapping judgement
Zhenhua Huang
quic_zhenhuah at quicinc.com
Thu Mar 16 05:19:51 PDT 2023
On 2023/3/16 18:36, Zhenhua Huang wrote:
>
>
> On 2023/3/16 18:06, Marco Elver wrote:
>> On Thu, Mar 16, 2023 at 04:50PM +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;
>>
>> This should not be accessible if !CONFIG_KFENCE.
>>
>>> +#ifdef CONFIG_KFENCE
>>> +
>>> +extern char *__kfence_pool;
>>> +static inline void kfence_set_pool(phys_addr_t addr)
>>> +{
>>> + __kfence_pool = phys_to_virt(addr);
>>> +}
>>
>> kfence_set_pool() is redundant if it's for arm64 only, because we know
>> where it's needed, and there you could just access __kfence_pool
>> directly. So let's just remove this function. (Initially I thought you
>> want to provide it generally, also for other architectures.)
>>
>>> +#else
>>> +
>>> +static inline void kfence_set_pool(phys_addr_t addr) { }
>>> +
>>> +#endif
>>> +
>>> static inline bool arch_kfence_init_pool(void) { return true; }
>> [...]
>>> +#endif
>>> +
>>> +phys_addr_t early_kfence_pool;
>>
>> This variable now exists in non-KFENCE builds, which is wrong.
>>
>>> 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);
>>> + }
>>
>> This whole piece of code could also be wrapped in another function,
>> which becomes a no-op if !CONFIG_KFENCE. Then you also don't need to
>> provide the KFENCE_POOL_SIZE define for 0 if !CONFIG_KFENCE.
>>
>> [...]
>>> + *
>>> + * 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);
>>
>> Accessing a non-existent variable if !CONFIG_KFENCE works because the
>> compiler optimizes out the access, but is generally bad style.
>
> Hi Marco,
>
> Actually my previous intention is not to do separation between KFENCE
> and non-KFENCE, instead to ensure early_kfence_pool always to be NULL in
> non-KFENCE build. That works well from my side w/ and w/o
> CONFIG_KFENCE.. but Yes that not clear to have this variable still in
> non-Kfence build.
>
> Sure, I will follow your suggestion below and tested on my side. Thanks.
>
> Thanks,
> Zhenhua
>
>>
>>
>> I think the only issue that I have is that the separation between KFENCE
>> and non-KFENCE builds is not great.
>>
>> At the end of the email are is a diff against your patch which would be
>> my suggested changes (while at it, I fixed up a bunch of other issues).
>> Untested, so if you decide to adopt these changes, please test.
Hi Marco,
All below seems well except minor change like we can't define
kfence_early_init as __initdata because it is used by non init function
like can_set_direct_map. Warning reported:
WARNING: modpost: vmlinux.o: section mismatch in reference:
can_set_direct_map (section: .text) -> kfence_early_init (section:
.init.data)
I have modified and sent out a new patchset. Please help review.
Thanks,
Zhenhua
>>
>> Thanks,
>> -- Marco
>>
>> ------ >8 ------
>>
>>
>> diff --git a/arch/arm64/include/asm/kfence.h
>> b/arch/arm64/include/asm/kfence.h
>> index 8143c91854e1..a81937fae9f6 100644
>> --- a/arch/arm64/include/asm/kfence.h
>> +++ b/arch/arm64/include/asm/kfence.h
>> @@ -10,22 +10,6 @@
>> #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)
>> @@ -35,4 +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 61944c7091f0..683958616ac1 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -528,17 +528,14 @@ 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;
>> -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)
>> +/* early_param() will be parsed before map_mem() below. */
>> +static int __init parse_kfence_early_init(char *arg)
>> {
>> int val;
>> - if (get_option(&p, &val))
>> + if (get_option(&arg, &val))
>> kfence_early_init = !!val;
>> return 0;
>> }
>> @@ -552,22 +549,34 @@ static phys_addr_t arm64_kfence_alloc_pool(void)
>> return 0;
>> kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
>> - if (!kfence_pool)
>> + 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;
>> }
>> -#else
>> -
>> -static phys_addr_t arm64_kfence_alloc_pool(void)
>> +static void arm64_kfence_map_pool(phys_addr_t kfence_pool, pgd_t *pgdp)
>> {
>> - return 0;
>> -}
>> -
>> -#endif
>> + if (!kfence_pool)
>> + return;
>> -phys_addr_t early_kfence_pool;
>> + /* 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)
>> {
>> @@ -575,6 +584,7 @@ static void __init map_mem(pgd_t *pgdp)
>> 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;
>> @@ -588,8 +598,6 @@ 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;
>> @@ -656,17 +664,7 @@ 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);
>> - }
>> + 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 7ce5295cc6fb..aa8fd12cc96f 100644
>> --- a/arch/arm64/mm/pageattr.c
>> +++ b/arch/arm64/mm/pageattr.c
>> @@ -7,7 +7,6 @@
>> #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>
>> @@ -28,11 +27,10 @@ bool can_set_direct_map(void)
>> * 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.
>> + * KFENCE pool requires page-granular mapping if initialized late.
>> */
>> return (rodata_enabled && rodata_full) ||
>> debug_pagealloc_enabled() ||
>> - (IS_ENABLED(CONFIG_KFENCE) && !early_kfence_pool);
>> + arm64_kfence_can_set_direct_map();
>> }
>> 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 91cbcc98e293..726857a4b680 100644
>> --- a/include/linux/kfence.h
>> +++ b/include/linux/kfence.h
>> @@ -222,7 +222,6 @@ 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_init(void) { }
>> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
>> index fab087d39633..e7f22af5e710 100644
>> --- a/mm/kfence/core.c
>> +++ b/mm/kfence/core.c
>> @@ -818,7 +818,7 @@ void __init kfence_alloc_pool(void)
>> if (!kfence_sample_interval)
>> return;
>> - /* if the pool has already been initialized by arch, skip the
>> below */
>> + /* If the pool has already been initialized by arch, skip the
>> below. */
>> if (__kfence_pool)
>> return;
>
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