[PATCH] mm,kfence: decouple kfence from page granularity mapping judgement
Marco Elver
elver at google.com
Thu Mar 9 03:09:22 PST 2023
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.
Thanks,
-- Marco
More information about the linux-arm-kernel
mailing list