On Tue, 14 Mar 2023 at 08:05, Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx> 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. > > LINK: [1] https://lore.kernel.org/linux-arm-kernel/Y+IsdrvDNILA59UN@FVFF77S0Q05N/ > Suggested-by: Mark Rutland <mark.rutland@xxxxxxx> > Signed-off-by: Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx> > --- > 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. 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. > static void kfence_init_enable(void) > { > if (!IS_ENABLED(CONFIG_KFENCE_STATIC_KEYS)) > -- > 2.7.4 >
