[PATCH v8] mm,kfence: decouple kfence from page granularity mapping judgement
Zhenhua Huang
quic_zhenhuah at quicinc.com
Tue Mar 14 03:31:52 PDT 2023
On 2023/3/14 16:41, Marco Elver wrote:
> On Tue, 14 Mar 2023 at 08:05, Zhenhua Huang <quic_zhenhuah at quicinc.com> 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 | 2 ++
>> arch/arm64/mm/mmu.c | 44 +++++++++++++++++++++++++++++++++++++++++
>> arch/arm64/mm/pageattr.c | 9 +++++++--
>> include/linux/kfence.h | 8 ++++++++
>> mm/kfence/core.c | 9 +++++++++
>> 5 files changed, 70 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h
>> index aa855c6..f1f9ca2d 100644
>> --- a/arch/arm64/include/asm/kfence.h
>> +++ b/arch/arm64/include/asm/kfence.h
>> @@ -10,6 +10,8 @@
>>
>> #include <asm/set_memory.h>
>>
>> +extern phys_addr_t early_kfence_pool;
>> +
>> 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..7fbf2ed 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 +527,33 @@ static int __init enable_crash_mem_map(char *arg)
>> }
>> early_param("crashkernel", enable_crash_mem_map);
>>
>> +#ifdef CONFIG_KFENCE
>> +
>> +static phys_addr_t arm64_kfence_alloc_pool(void)
>> +{
>> + phys_addr_t kfence_pool;
>> +
>> + if (!kfence_sample_interval)
>> + 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;
>
> The compiler will not optimize out this global. This now exists in all
> arm64 kernel builds.
>
> Furthermore, there's no need for this to be phys_addr_t. Nothing
> outside map_mem() needs the address, so this can just be a bool.
Seems we need this early_kfence_bool to be explicit phys_addr_t as we
need to mark/clear NOMAP for the region, so that it will not do linear
mapping in the for loop.
>
> I'd recommend moving the variable under CONFIG_KFENCE, and in the asm
> header, just having a static inline helper function e.g.
> arm64_kfence_early_pool(). That helper just returns false in the
> !CONFIG_KFENCE case.
>
>> static void __init map_mem(pgd_t *pgdp)
>> {
>> static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN);
>> @@ -543,6 +572,10 @@ 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 +641,17 @@ 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);
>> + }
>> }
>>
>> void mark_rodata_ro(void)
>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>> index 79dd201..7ce5295 100644
>> --- a/arch/arm64/mm/pageattr.c
>> +++ b/arch/arm64/mm/pageattr.c
>> @@ -7,10 +7,12 @@
>> #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>
>> #include <asm/tlbflush.h>
>> +#include <asm/kfence.h>
>>
>> struct page_change_data {
>> pgprot_t set_mask;
>> @@ -22,12 +24,15 @@ 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 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);
>> }
>>
>> 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..570d4e3 100644
>> --- a/include/linux/kfence.h
>> +++ b/include/linux/kfence.h
>> @@ -64,6 +64,12 @@ static __always_inline bool is_kfence_address(const void *addr)
>> void __init kfence_alloc_pool(void);
>>
>> /**
>> + * kfence_set_pool() - allows an arch to set the
>> + * KFENCE pool during early init
>> + */
>> +void __init kfence_set_pool(phys_addr_t addr);
>> +
>> +/**
>> * kfence_init() - perform KFENCE initialization at boot time
>> *
>> * Requires that kfence_alloc_pool() was called before. This sets up the
>> @@ -222,8 +228,10 @@ 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_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/mm/kfence/core.c b/mm/kfence/core.c
>> index 5349c37..0765395 100644
>> --- a/mm/kfence/core.c
>> +++ b/mm/kfence/core.c
>> @@ -814,12 +814,21 @@ 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)
>> pr_err("failed to allocate pool\n");
>> }
>>
>> +void __init kfence_set_pool(phys_addr_t addr)
>> +{
>> + __kfence_pool = phys_to_virt(addr);
>> +}
>
> Please move this function to the header as a static inline function,
> because nothing else other than arm64 needs this, having this function
> be here introduces a .text size increase for everyone.
>
> The function is so short that having it as a static inline function is
> fine, and will save a few bytes of .text.
Reasonable! Thanks!
>
>> static void kfence_init_enable(void)
>> {
>> if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS))
>> --
>> 2.7.4
>>
Thanks,
Zhenhua
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