linux-kernel - RE: [PATCH AUTOSEL 5.3 169/203] x86/platform/uv: Fix kmalloc() NULL check routine

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Message-ID: <ea163ee8ba4446978732c2c6607bd6da@AcuMS.aculab.com>
Date:   Wed, 2 Oct 2019 08:34:08 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Sasha Levin' <sashal@...nel.org>,
        Greg KH <gregkh@...uxfoundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Austin Kim <austindh.kim@...il.com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        "Hedi Berriche" <hedi.berriche@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mike Travis <mike.travis@....com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Russ Anderson <russ.anderson@....com>,
        "Steve Wahl" <steve.wahl@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "allison@...utok.net" <allison@...utok.net>,
        "andy@...radead.org" <andy@...radead.org>,
        "armijn@...ldur.nl" <armijn@...ldur.nl>,
        "bp@...en8.de" <bp@...en8.de>,
        "dvhart@...radead.org" <dvhart@...radead.org>,
        "hpa@...or.com" <hpa@...or.com>, "kjlu@....edu" <kjlu@....edu>,
        "platform-driver-x86@...r.kernel.org" 
        <platform-driver-x86@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>
Subject: RE: [PATCH AUTOSEL 5.3 169/203] x86/platform/uv: Fix kmalloc() NULL
 check routine

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@...il.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@...il.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

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