Re: [PATCH AUTOSEL 5.3 169/203] x86/platform/uv: Fix kmalloc() NULL check routine

Mike Travis
2019-10-02T14:37:11Z

On 10/2/2019 1:34 AM, David Laight wrote:
> From: Sasha Levin
>> Sent: 01 October 2019 17:06
>> Subject: Re: [PATCH AUTOSEL 5.3 169/203] x86/platform/uv: Fix kmalloc() NULL check routine
>>
>> On Sun, Sep 22, 2019 at 10:25:44PM +0200, Greg KH wrote:
>>> On Sun, Sep 22, 2019 at 02:43:15PM -0400, Sasha Levin wrote:
>>>> From: Austin Kim <austindh.kim@gmail.com>
>>>>
>>>> [ Upstream commit 864b23f0169d5bff677e8443a7a90dfd6b090afc ]
>>>>
>>>> The result of kmalloc() should have been checked ahead of below statement:
>>>>
>>>> pqp = (struct bau_pq_entry *)vp;
>>>>
>>>> Move BUG_ON(!vp) before above statement.
>>>>
>>>> Signed-off-by: Austin Kim <austindh.kim@gmail.com>
> ...
>>>> ---
>>>> arch/x86/platform/uv/tlb_uv.c | 4 ++--
>>>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/arch/x86/platform/uv/tlb_uv.c b/arch/x86/platform/uv/tlb_uv.c
>>>> index 20c389a91b803..5f0a96bf27a1f 100644
>>>> --- a/arch/x86/platform/uv/tlb_uv.c
>>>> +++ b/arch/x86/platform/uv/tlb_uv.c
>>>> @@ -1804,9 +1804,9 @@ static void pq_init(int node, int pnode)
>>>>
>>>> plsize = (DEST_Q_SIZE + 1) * sizeof(struct bau_pq_entry);
>>>> vp = kmalloc_node(plsize, GFP_KERNEL, node);
>>>> - pqp = (struct bau_pq_entry *)vp;
>>>> - BUG_ON(!pqp);
>>>> + BUG_ON(!vp);
>>>>
>>>> + pqp = (struct bau_pq_entry *)vp;
>>>> cp = (char *)pqp + 31;
>>>> pqp = (struct bau_pq_entry *)(((unsigned long)cp >> 5) << 5);
>>>>
>>>
>>> How did this even get merged in the first place? I thought a number of
>>> us complained about it.
>>>
>>> This isn't any change in code, and the original is just fine, the author
>>> didn't realize how C works :(
>
> Mind you, the code itself if pretty horrid.
> Looks like it is aligning to 32 bytes, easier done by:
> pqp = (void *)((unsigned long)vp + 31 & ~31);
> (and there's a roundup macro to obfuscate it somewhere.)
> But I'd also expect to see a matching '+ 31' in the size passed to kmalloc().
> Not to mention a comment!
>
> David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>

Thanks, I will put all of these comments in my notes. This whole
function is slated to move to a specialized UV APIC driver since it uses
a unique scaling feature available in the UV hardware. (The original
author has long retired.)

-Mike