Date:   Wed, 22 Dec 2021 11:11:07 +0000
From:   Catalin Marinas <catalin.marinas@arm.com>
To:     andrey.konovalov@linux.dev
Cc:     Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        kasan-dev@googlegroups.com, linux-mm@kvack.org,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        Peter Collingbourne <pcc@google.com>,
        Evgenii Stepanov <eugenis@google.com>,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: Re: [PATCH mm v4 32/39] kasan, arm64: don't tag executable vmalloc
 allocations
Message-ID: <YcMHyxOIN0LD7Lrt@arm.com>
References: <cover.1640036051.git.andreyknvl@google.com>
 <85ecef50788a3915a9a8fb52e97207901f27b057.1640036051.git.andreyknvl@google.com>
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On Mon, Dec 20, 2021 at 11:02:04PM +0100, andrey.konovalov@linux.dev wrote:
> From: Andrey Konovalov <andreyknvl@google.com>
> 
> Besides asking vmalloc memory to be executable via the prot argument
> of __vmalloc_node_range() (see the previous patch), the kernel can skip
> that bit and instead mark memory as executable via set_memory_x().
> 
> Once tag-based KASAN modes start tagging vmalloc allocations, executing
> code from such allocations will lead to the PC register getting a tag,
> which is not tolerated by the kernel.
> 
> Generic kernel code typically allocates memory via module_alloc() if
> it intends to mark memory as executable. (On arm64 module_alloc()
> uses __vmalloc_node_range() without setting the executable bit).
> 
> Thus, reset pointer tags of pointers returned from module_alloc().
> 
> However, on arm64 there's an exception: the eBPF subsystem. Instead of
> using module_alloc(), it uses vmalloc() (via bpf_jit_alloc_exec())
> to allocate its JIT region.
> 
> Thus, reset pointer tags of pointers returned from bpf_jit_alloc_exec().
> 
> Resetting tags for these pointers results in untagged pointers being
> passed to set_memory_x(). This causes conflicts in arithmetic checks
> in change_memory_common(), as vm_struct->addr pointer returned by
> find_vm_area() is tagged.
> 
> Reset pointer tag of find_vm_area(addr)->addr in change_memory_common().
> 
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> 

Acked-by: Catalin Marinas <catalin.marinas@arm.com>