From: Catalin Marinas <catalin.marinas@arm.com>
To: Will Deacon <will@kernel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org
Subject: Re: [PATCH 1/5] arm64: vdso: don't free unallocated pages
Date: Wed, 15 Apr 2020 11:08:37 +0100 [thread overview]
Message-ID: <20200415100836.GB6526@gaia> (raw)
In-Reply-To: <20200414151033.GA30288@willie-the-truck>
On Tue, Apr 14, 2020 at 04:10:35PM +0100, Will Deacon wrote:
> On Tue, Apr 14, 2020 at 03:53:45PM +0100, Vincenzo Frascino wrote:
> > On 4/14/20 2:27 PM, Mark Rutland wrote:
> > > On Tue, Apr 14, 2020 at 01:50:38PM +0100, Vincenzo Frascino wrote:
> > >> On 4/14/20 11:42 AM, Mark Rutland wrote:
> > >>> The aarch32_vdso_pages[] array never has entries allocated in the C_VVAR
> > >>> or C_VDSO slots, and as the array is zero initialized these contain
> > >>> NULL.
> > >>>
> > >>> However in __aarch32_alloc_vdso_pages() when
> > >>> aarch32_alloc_kuser_vdso_page() fails we attempt to free the page whose
> > >>> struct page is at NULL, which is obviously nonsensical.
> > >>
> > >> Could you please explain why do you think that free(NULL) is "nonsensical"?
> > >
> > > Regardless of the below, can you please explain why it is sensical? I'm
> > > struggling to follow your argument here.
> >
> > free(NULL) is a no-operation ("no action occurs") according to the C standard
> > (ISO-IEC 9899 paragraph 7.20.3.2). Hence this should not cause any bug if the
> > allocator is correctly implemented. From what I can see the implementation of
> > the page allocator honors this assumption.
> >
> > Since you say it is a bug (providing evidence), we might have to investigate
> > because probably there is an issue somewhere else.
>
> Not sure why you feel the need to throw the C standard around -- the patch
> from Mark looks obviously like the right thing to do to me, so:
>
> Acked-by: Will Deacon <will@kernel.org>
>
> Catalin -- please take this one as a fix so that I can queue the rest of
> the patches for 5.8 once it's hit mainline.
I queued this patch for -rc2. Thanks.
--
Catalin
next prev parent reply other threads:[~2020-04-15 10:08 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200414104252.16061-1-mark.rutland@arm.com>
2020-04-14 10:42 ` [PATCH 1/5] arm64: vdso: don't free unallocated pages Mark Rutland
2020-04-14 12:50 ` Vincenzo Frascino
2020-04-14 13:27 ` Mark Rutland
2020-04-14 14:53 ` Vincenzo Frascino
2020-04-14 15:10 ` Will Deacon
2020-04-15 10:08 ` Catalin Marinas [this message]
2020-04-14 15:12 ` Mark Rutland
2020-04-14 15:27 ` Vincenzo Frascino
2020-04-14 15:59 ` Catalin Marinas
2020-04-15 10:13 ` Catalin Marinas
2020-04-15 13:03 ` Mark Rutland
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