linux-kernel - Re: [PATCH] usercopy: Add tests for all get

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Message-ID: <CAGXu5j+MtxHxiPbSG3+6Tuw3EkBPixO73GYn692Nfoi1AwPWZw@mail.gmail.com>
Date:   Wed, 15 Feb 2017 09:06:25 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Hoeun Ryu <hoeun.ryu@...il.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCH] usercopy: Add tests for all get_user() sizes

On Wed, Feb 15, 2017 at 12:50 AM, Geert Uytterhoeven
<geert@...ux-m68k.org> wrote:
> On Tue, Feb 14, 2017 at 9:40 PM, Kees Cook <keescook@...omium.org> wrote:
>> The existing test was only exercising native unsigned long size
>> get_user(). For completeness, we should check all sizes.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  lib/test_user_copy.c | 45 ++++++++++++++++++++++++++++++++++-----------
>>  1 file changed, 34 insertions(+), 11 deletions(-)
>>
>> diff --git a/lib/test_user_copy.c b/lib/test_user_copy.c
>> index ac3a60ba9331..49569125b7c5 100644
>> --- a/lib/test_user_copy.c
>> +++ b/lib/test_user_copy.c
>> @@ -40,8 +40,11 @@ static int __init test_user_copy_init(void)
>>         char __user *usermem;
>>         char *bad_usermem;
>>         unsigned long user_addr;
>> -       unsigned long value = 0x5A;
>>         char *zerokmem;
>> +       u8 val_u8;
>> +       u16 val_u16;
>> +       u32 val_u32;
>> +       u64 val_u64;
>>
>>         kmem = kmalloc(PAGE_SIZE * 2, GFP_KERNEL);
>>         if (!kmem)
>> @@ -72,10 +75,20 @@ static int __init test_user_copy_init(void)
>>                     "legitimate copy_from_user failed");
>>         ret |= test(copy_to_user(usermem, kmem, PAGE_SIZE),
>>                     "legitimate copy_to_user failed");
>> -       ret |= test(get_user(value, (unsigned long __user *)usermem),
>> -                   "legitimate get_user failed");
>> -       ret |= test(put_user(value, (unsigned long __user *)usermem),
>> -                   "legitimate put_user failed");
>> +
>> +#define test_legit(size)                                                 \
>> +       do {                                                              \
>> +               ret |= test(get_user(val_##size, (size __user *)usermem), \
>> +                   "legitimate get_user (" #size ") failed");            \
>> +               ret |= test(put_user(val_##size, (size __user *)usermem), \
>> +                   "legitimate put_user (" #size ") failed");            \
>> +       } while (0)
>> +
>> +       test_legit(u8);
>> +       test_legit(u16);
>> +       test_legit(u32);
>> +       test_legit(u64);
>> +#undef test_legit
>
> ERROR: "__get_user_bad" [lib/test_user_copy.ko] undefined!
>
> http://kisskb.ellerman.id.au/kisskb/buildresult/12936728/
>
> So 64-bit get_user() support is mandatory now?

That's not my intention. :) In my sampling of architectures, I missed
a couple 32-bit archs that don't support 64-bit getuser(). I'm not
sure how to correctly write these tests, though, since it seems rather
ad-hoc. e.g. m68k has 64-bit getuser() commented out due to an old gcc
bug...

Should I just universally skip 64-bit getuser on 32-bit archs?

-Kees

-- 
Kees Cook
Pixel Security