Messages in this thread | | | From | Marco Elver <> | Date | Fri, 2 Oct 2020 16:18:48 +0200 | Subject | Re: [PATCH v4 03/11] arm64, kfence: enable KFENCE for ARM64 |
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On Fri, 2 Oct 2020 at 08:48, Jann Horn <jannh@google.com> wrote: > > On Tue, Sep 29, 2020 at 3:38 PM Marco Elver <elver@google.com> wrote: > > Add architecture specific implementation details for KFENCE and enable > > KFENCE for the arm64 architecture. In particular, this implements the > > required interface in <asm/kfence.h>. Currently, the arm64 version does > > not yet use a statically allocated memory pool, at the cost of a pointer > > load for each is_kfence_address(). > [...] > > diff --git a/arch/arm64/include/asm/kfence.h b/arch/arm64/include/asm/kfence.h > [...] > > +static inline bool arch_kfence_initialize_pool(void) > > +{ > > + const unsigned int num_pages = ilog2(roundup_pow_of_two(KFENCE_POOL_SIZE / PAGE_SIZE)); > > + struct page *pages = alloc_pages(GFP_KERNEL, num_pages); > > + > > + if (!pages) > > + return false; > > + > > + __kfence_pool = page_address(pages); > > + return true; > > +} > > If you're going to do "virt_to_page(meta->addr)->slab_cache = cache;" > on these pages in kfence_guarded_alloc(), and pass them into kfree(), > you'd better mark these pages as non-compound - something like > alloc_pages_exact() or split_page() may help. Otherwise, I think when > SLUB's kfree() does virt_to_head_page() right at the start, that will > return a pointer to the first page of the entire __kfence_pool, and > then when it loads page->slab_cache, it gets some random cache and > stuff blows up. Kinda surprising that you haven't run into that during > your testing, maybe I'm missing something...
I added a WARN_ON() check in kfence_initialize_pool() to check if our pages are compound or not; they are not.
In slub.c, __GFP_COMP is passed to alloc_pages(), which causes them to have a compound head I believe.
> Also, this kinda feels like it should be the "generic" version of > arch_kfence_initialize_pool() and live in mm/kfence/core.c ?
Done for v5.
Thanks, -- Marco
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