[PATCH] mm,kfence: decouple kfence from page granularity mapping judgement
Zhenhua Huang
quic_zhenhuah at quicinc.com
Thu Mar 9 03:26:02 PST 2023
Thanks Marco!
On 2023/3/9 19:09, Marco Elver wrote:
> On Thu, 9 Mar 2023 at 12:04, Zhenhua Huang <quic_zhenhuah at quicinc.com> wrote:
>>
>> Thanks Marco.
>>
>> On 2023/3/9 18:33, Marco Elver wrote:
>>> On Thu, 9 Mar 2023 at 09:05, Zhenhua Huang <quic_zhenhuah at quicinc.com> wrote:
>>>>
>>>> Kfence only needs its pool to be mapped as page granularity, previous
>>>> judgement was a bit over protected. Decouple it from judgement and do
>>>> page granularity mapping for kfence pool only [1].
>>>>
>>>> To implement this, also relocate the kfence pool allocation before the
>>>> linear mapping setting up, 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/1675750519-1064-1-git-send-email-quic_zhenhuah@quicinc.com/T/
>>>> Suggested-by: Mark Rutland <mark.rutland at arm.com>
>>>> Signed-off-by: Zhenhua Huang <quic_zhenhuah at quicinc.com>
>>>> ---
>>>> arch/arm64/mm/mmu.c | 24 ++++++++++++++++++++++++
>>>> arch/arm64/mm/pageattr.c | 5 ++---
>>>> include/linux/kfence.h | 10 ++++++++--
>>>> init/main.c | 1 -
>>>> mm/kfence/core.c | 18 ++++++++++++++----
>>>> 5 files changed, 48 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>>>> index 6f9d889..bd79691 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>
>>>> @@ -532,6 +533,9 @@ static void __init map_mem(pgd_t *pgdp)
>>>> phys_addr_t kernel_end = __pa_symbol(__init_begin);
>>>> phys_addr_t start, end;
>>>> int flags = NO_EXEC_MAPPINGS;
>>>> +#ifdef CONFIG_KFENCE
>>>> + phys_addr_t kfence_pool = 0;
>>>> +#endif
>>>> u64 i;
>>>>
>>>> /*
>>>> @@ -564,6 +568,12 @@ static void __init map_mem(pgd_t *pgdp)
>>>> }
>>>> #endif
>>>>
>>>> +#ifdef CONFIG_KFENCE
>>>> + kfence_pool = kfence_alloc_pool();
>>>> + if (kfence_pool)
>>>> + memblock_mark_nomap(kfence_pool, KFENCE_POOL_SIZE);
>>>> +#endif
>>>> +
>>>> /* map all the memory banks */
>>>> for_each_mem_range(i, &start, &end) {
>>>> if (start >= end)
>>>> @@ -608,6 +618,20 @@ static void __init map_mem(pgd_t *pgdp)
>>>> }
>>>> }
>>>> #endif
>>>> +
>>>> + /* Kfence pool needs page-level mapping */
>>>> +#ifdef CONFIG_KFENCE
>>>> + if (kfence_pool) {
>>>> + __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 really mapped now */
>>>> + kfence_set_pool(kfence_pool);
>>>> + }
>>>> +#endif
>>>> +
>>>> }
>>>>
>>>> void mark_rodata_ro(void)
>>>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>>>> index 79dd201..61156d0 100644
>>>> --- a/arch/arm64/mm/pageattr.c
>>>> +++ b/arch/arm64/mm/pageattr.c
>>>> @@ -22,12 +22,11 @@ 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.
>>>> */
>>>> - return (rodata_enabled && rodata_full) || debug_pagealloc_enabled() ||
>>>> - IS_ENABLED(CONFIG_KFENCE);
>>>> + return (rodata_enabled && rodata_full) || debug_pagealloc_enabled();
>>>> }
>>>>
>>>> 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..0252e74 100644
>>>> --- a/include/linux/kfence.h
>>>> +++ b/include/linux/kfence.h
>>>> @@ -61,7 +61,12 @@ static __always_inline bool is_kfence_address(const void *addr)
>>>> /**
>>>> * kfence_alloc_pool() - allocate the KFENCE pool via memblock
>>>> */
>>>> -void __init kfence_alloc_pool(void);
>>>> +phys_addr_t __init kfence_alloc_pool(void);
>>>> +
>>>> +/**
>>>> + * kfence_set_pool() - KFENCE pool mapped and can be used
>>>> + */
>>>> +void __init kfence_set_pool(phys_addr_t addr);
>>>>
>>>> /**
>>>> * kfence_init() - perform KFENCE initialization at boot time
>>>> @@ -223,7 +228,8 @@ bool __kfence_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *sla
>>>> #else /* CONFIG_KFENCE */
>>>>
>>>> static inline bool is_kfence_address(const void *addr) { return false; }
>>>> -static inline void kfence_alloc_pool(void) { }
>>>> +static inline phys_addr_t kfence_alloc_pool(void) { return (phys_addr_t)NULL; }
>>>> +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/init/main.c b/init/main.c
>>>> index 4425d17..9aaf217 100644
>>>> --- a/init/main.c
>>>> +++ b/init/main.c
>>>> @@ -839,7 +839,6 @@ static void __init mm_init(void)
>>>> */
>>>> page_ext_init_flatmem();
>>>> init_mem_debugging_and_hardening();
>>>> - kfence_alloc_pool();
>>>
>>> This breaks other architectures.
>>
>> Nice catch. Thanks!
>>
>>>
>>>> report_meminit();
>>>> kmsan_init_shadow();
>>>> stack_depot_early_init();
>>>> diff --git a/mm/kfence/core.c b/mm/kfence/core.c
>>>> index 5349c37..dd5cdd5 100644
>>>> --- a/mm/kfence/core.c
>>>> +++ b/mm/kfence/core.c
>>>> @@ -809,15 +809,25 @@ static void toggle_allocation_gate(struct work_struct *work)
>>>>
>>>> /* === Public interface ===================================================== */
>>>>
>>>> -void __init kfence_alloc_pool(void)
>>>> +phys_addr_t __init kfence_alloc_pool(void)
>>>> {
>>>
>>> You could just return here:
>>>
>>> if (__kfence_pool)
>>> return; /* Initialized earlier by arch init code. */
>>
>> Yeah.
>>
>>>
>>> ... and see my comments below.
>>>
>>>> + phys_addr_t kfence_pool;
>>>> if (!kfence_sample_interval)
>>>> - return;
>>>> + return 0;
>>>>
>>>> - __kfence_pool = memblock_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
>>>> + kfence_pool = memblock_phys_alloc(KFENCE_POOL_SIZE, PAGE_SIZE);
>>>>
>>>> - if (!__kfence_pool)
>>>> + if (!kfence_pool) {
>>>> pr_err("failed to allocate pool\n");
>>>> + return 0;
>>>> + }
>>>> +
>>>> + return kfence_pool;
>>>> +}
>>>> +
>>>> +void __init kfence_set_pool(phys_addr_t addr)
>>>> +{
>>>> + __kfence_pool = phys_to_virt(addr);
>>>> }
>>>
>>> I would suggest leaving kfence_alloc_pool() to return nothing (with
>>> the addition above), and just set __kfence_pool as before.
>>> __kfence_pool itself is exported by include/linux/kfence.h, so if you
>>> call kfence_alloc_pool() in arm64 earlier, you can access
>>> __kfence_pool to get the allocated pool.
>>
>> Shall we add one new function like arm64_kfence_alloc_pool() ? The
>> reason is linear mapping at that time not set up and we must alloc phys
>> addr based on memblock. We can't use common kfence_alloc_pool()..
>
> Ah right - well, you can initialize __kfence_pool however you like
> within arm64 init code. Just teaching kfence_alloc_pool() to do
> nothing if it's already initialized should be enough. Within
> arch/arm64/mm/mmu.c it might be nice to factor out some bits into a
> helper like arm64_kfence_alloc_pool(), but would just stick to
> whatever is simplest.
Many thanks Marco. Let me conclude as following:
1. put arm64_kfence_alloc_pool() within arch/arm64/mm/mmu.c as it's
arch_ specific codes.
2. leave kfence_set_pool() to set _kfence_pool within kfence driver, as
it may become common part.
The reason we still need #2 is because _kfence_pool only can be used
after mapping set up, it must be late than pool allocation. Do you have
any further suggestion?
>
> Thanks,
> -- Marco
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