linux-kernel - Re: [PATCH v2 1/2] powerpc: Fix virt_addr

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Message-ID: <b377978c-7953-ba08-c775-f2f991c9932c@csgroup.eu>
Date:   Mon, 10 Jan 2022 08:01:38 +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 1/2] powerpc: Fix virt_addr_valid() check



Le 25/12/2021 à 13:06, Kefeng Wang a écrit :
> When run ethtool eth0, the BUG occurred,
> 
>    usercopy: Kernel memory exposure attempt detected from SLUB object not in SLUB page?! (offset 0, size 1048)!
>    kernel BUG at mm/usercopy.c:99
>    ...
>    usercopy_abort+0x64/0xa0 (unreliable)
>    __check_heap_object+0x168/0x190
>    __check_object_size+0x1a0/0x200
>    dev_ethtool+0x2494/0x2b20
>    dev_ioctl+0x5d0/0x770
>    sock_do_ioctl+0xf0/0x1d0
>    sock_ioctl+0x3ec/0x5a0
>    __se_sys_ioctl+0xf0/0x160
>    system_call_exception+0xfc/0x1f0
>    system_call_common+0xf8/0x200
> 
> The code shows below,
> 
>    data = vzalloc(array_size(gstrings.len, ETH_GSTRING_LEN));
>    copy_to_user(useraddr, data, gstrings.len * ETH_GSTRING_LEN))
> 
> The data is alloced by vmalloc(), virt_addr_valid(ptr) will return true
> on PowerPC64, which leads to the panic.
> 
> As commit 4dd7554a6456 ("powerpc/64: Add VIRTUAL_BUG_ON checks for __va
> and __pa addresses") does, make sure the virt addr above PAGE_OFFSET in
> the virt_addr_valid().

The change done by that commit only applies to PPC64.

The change you are doing applies to both PPC64 and PPC32. Did you verify 
the impact (or should I say the absence of impact) on PPC32 ?

> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> ---
>   arch/powerpc/include/asm/page.h | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
> index 254687258f42..300d4c105a3a 100644
> --- a/arch/powerpc/include/asm/page.h
> +++ b/arch/powerpc/include/asm/page.h
> @@ -132,7 +132,10 @@ static inline bool pfn_valid(unsigned long pfn)
>   #define virt_to_page(kaddr)	pfn_to_page(virt_to_pfn(kaddr))
>   #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)
>   
> -#define virt_addr_valid(kaddr)	pfn_valid(virt_to_pfn(kaddr))
> +#define virt_addr_valid(vaddr)	({						\
> +	unsigned long _addr = (unsigned long)vaddr;				\
> +	(unsigned long)(_addr) >= PAGE_OFFSET && pfn_valid(virt_to_pfn(_addr));	\

_addr is already an 'unsigned long' so you shouldnt need to cast it.

> +})
>   
>   /*
>    * On Book-E parts we need __va to parse the device tree and we can't