linux-kernel - Re: [PATCH] Revert "mm/usercopy: Drop extra is_vmalloc_or

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Date:   Fri, 24 Dec 2021 06:01:07 +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>
Subject: Re: [PATCH] Revert "mm/usercopy: Drop extra is_vmalloc_or_module()
 check"



Le 23/12/2021 à 11:21, Kefeng Wang a écrit :
> This reverts commit 517e1fbeb65f5eade8d14f46ac365db6c75aea9b.
> 
>    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
> 
> When run ethtool eth0, the BUG occurred, 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, add back the is_vmalloc_or_module()
> check to fix it.

Is it expected that virt_addr_valid() returns true on PPC64 for 
vmalloc'ed memory ? If that's the case it also means that 
CONFIG_DEBUG_VIRTUAL won't work as expected either.

If it is unexpected, I think you should fix PPC64 instead of adding this 
hack back. Maybe the ARM64 fix can be used as a starting point, see 
commit 68dd8ef32162 ("arm64: memory: Fix virt_addr_valid() using 
__is_lm_address()")

In the meantime, can you provide more information on your config, 
especially which memory model is used ?

Christophe