linux-kernel - Re: [PATCH mm v3 31/38] kasan, arm64: don't tag executable vmalloc allocations

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Date:   Mon, 13 Dec 2021 22:59:35 +0100
From:   Andrey Konovalov <andreyknvl@...il.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     Marco Elver <elver@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Peter Collingbourne <pcc@...gle.com>,
        Evgenii Stepanov <eugenis@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        andrey.konovalov@...ux.dev
Subject: Re: [PATCH mm v3 31/38] kasan, arm64: don't tag executable vmalloc allocations

On Mon, Dec 13, 2021 at 10:55 PM <andrey.konovalov@...ux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@...gle.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().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@...gle.com>
>
> ---
>
> Changes v2->v3:
> - Add this patch.
> ---
>  arch/arm64/kernel/module.c    | 3 ++-
>  arch/arm64/net/bpf_jit_comp.c | 3 ++-
>  2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
> index d3a1fa818348..f2d4bb14bfab 100644
> --- a/arch/arm64/kernel/module.c
> +++ b/arch/arm64/kernel/module.c
> @@ -63,7 +63,8 @@ void *module_alloc(unsigned long size)
>                 return NULL;
>         }
>
> -       return p;
> +       /* Memory is intended to be executable, reset the pointer tag. */
> +       return kasan_reset_tag(p);
>  }
>
>  enum aarch64_reloc_op {
> diff --git a/arch/arm64/net/bpf_jit_comp.c b/arch/arm64/net/bpf_jit_comp.c
> index 07aad85848fa..381a67922c2d 100644
> --- a/arch/arm64/net/bpf_jit_comp.c
> +++ b/arch/arm64/net/bpf_jit_comp.c
> @@ -1147,7 +1147,8 @@ u64 bpf_jit_alloc_exec_limit(void)
>
>  void *bpf_jit_alloc_exec(unsigned long size)
>  {
> -       return vmalloc(size);
> +       /* Memory is intended to be executable, reset the pointer tag. */
> +       return kasan_reset_tag(vmalloc(size));
>  }
>
>  void bpf_jit_free_exec(void *addr)
> --
> 2.25.1
>

Catalin, Vincenzo,

This is a new patch added in v3. Could you PTAL? Thanks!