linux-kernel - Re: [PATCH v2 2/2] mm: usercopy: Warn vmalloc/module address in check_heap

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Date:   Sun, 26 Dec 2021 17:33:43 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Kees Cook <keescook@...omium.org>,
        Laura Abbott <labbott@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>
CC:     Nicholas Piggin <npiggin@...il.com>
Subject: Re: [PATCH v2 2/2] mm: usercopy: Warn vmalloc/module address in
 check_heap_object()



Le 25/12/2021 à 13:06, Kefeng Wang a écrit :
> virt_addr_valid() could be insufficient to validate the virt addr
> on some architecture, which could lead to potential BUG which has
> been found on arm64/powerpc64.
> 
> Let's add WARN_ON to check if the virt addr is passed virt_addr_valid()
> but is a vmalloc/module address.

I think that's the responsibility of the architecture and doesn't 
deserve a WARN_ON() in generic code.

The generic code cannot check all what architectures do wrong.

Eventually you can do some testing at startup, maybe with 
CONFIG_DEBUG_VM_PGTABLE, but I don't think we should have such 
verification in functions like check_heap_object()

> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
>   mm/usercopy.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index b3de3c4eefba..ce83e0b137dd 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -228,6 +228,8 @@ static inline void check_heap_object(const void *ptr, unsigned long n,
>   	if (!virt_addr_valid(ptr))
>   		return;
>   
> +	WARN_ON_ONCE(is_vmalloc_or_module_addr(ptr));
> +
>   	/*
>   	 * When CONFIG_HIGHMEM=y, kmap_to_page() will give either the
>   	 * highmem page or fallback to virt_to_page(). The following