Date:   Fri, 7 Jan 2022 13:42:53 +0200
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Dave Hansen <dave.hansen@intel.com>
Cc:     Nathan Chancellor <nathan@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>, reinette.chatre@intel.com,
        linux-kernel@vger.kernel.org, linux-sgx@vger.kernel.org
Subject: Re: [PATCH v13 2/2] x86/sgx: Add an attribute for the amount of SGX
 memory in a NUMA node
Message-ID: <YdgnPTE5cnrptniM@iki.fi>
References: <20211116162116.93081-1-jarkko@kernel.org>
 <20211116162116.93081-2-jarkko@kernel.org>
 <YbzhBrimHGGpddDM@archlinux-ax161>
 <YcuhhI2+k0XVuTb1@iki.fi>
 <c857c964-89b9-d827-74ec-32cf874e8d8b@intel.com>
 <YddAiHSSX0V7UUik@iki.fi>
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On Thu, Jan 06, 2022 at 09:18:35PM +0200, Jarkko Sakkinen wrote:
> On Sat, Jan 01, 2022 at 08:54:51PM -0800, Dave Hansen wrote:
> > On 12/28/21 3:45 PM, Jarkko Sakkinen wrote:
> > >> If I can provide any further information or testing, let me know!
> > > Dave, when is the fix going to be applied [*]?
> > > 
> > >> Cheers,
> > >> Nathan
> > > [*] https://lore.kernel.org/linux-sgx/YcGTePmWDMOQU1pn@iki.fi/T/#m831a01bdde347f9e0af2c973986fae0499718201
> > 
> > Greg preferred hiding the file as opposed to faking a number in there.
> > Any testing of the attached would be appreciated.
> 
> > 
> > From: Dave Hansen <dave.hansen@linux.intel.com>
> > 
> > Nathan Chancellor reported an oops when aceessing the
> > 'sgx_total_bytes' sysfs file:
> > 
> > 	https://lore.kernel.org/all/YbzhBrimHGGpddDM@archlinux-ax161/
> > 
> > The sysfs output code accesses the sgx_numa_nodes[] array
> > unconditionally.  However, this array is allocated during SGX
> > initialization, which only occurs on systems where SGX is
> > supported.
> > 
> > If the sysfs file is accessed on systems without SGX support,
> > sgx_numa_nodes[] is NULL and an oops occurs.
> > 
> > To fix this, hide the entire nodeX/x86/ attribute group on
> > systems without SGX support using the ->is_visible attribute
> > group callback.
> > 
> > Fixes: 50468e431335 ("x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node")
> > Reported-by: Nathan Chancellor <nathan@kernel.org>
> > CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Jarkko Sakkinen <jarkko@kernel.org>
> > Cc: linux-sgx@vger.kernel.org
> > Cc: x86@kernel.org
> > Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> > ---
> > 
> >  b/arch/x86/kernel/cpu/sgx/main.c |   11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff -puN arch/x86/kernel/cpu/sgx/main.c~sgx-null-ptr arch/x86/kernel/cpu/sgx/main.c
> > --- a/arch/x86/kernel/cpu/sgx/main.c~sgx-null-ptr	2021-12-20 07:56:38.309584807 -0800
> > +++ b/arch/x86/kernel/cpu/sgx/main.c	2021-12-20 08:17:28.997705149 -0800
> > @@ -910,6 +910,16 @@ static ssize_t sgx_total_bytes_show(stru
> >  }
> >  static DEVICE_ATTR_RO(sgx_total_bytes);
> >  
> > +static umode_t arch_node_attr_is_visible(struct kobject * kobj,
> > +		struct attribute * attr, int idx)
> > +{
> > +	/* Make all x86/ attributes invisible when SGX is not initialized: */
> > +	if (nodes_empty(sgx_numa_mask))
> > +		return 0;
> > +
> > +	return attr->mode;
> > +}
> > +
> >  static struct attribute *arch_node_dev_attrs[] = {
> >  	&dev_attr_sgx_total_bytes.attr,
> >  	NULL,
> > @@ -918,6 +928,7 @@ static struct attribute *arch_node_dev_a
> >  const struct attribute_group arch_node_dev_group = {
> >  	.name = "x86",
> >  	.attrs = arch_node_dev_attrs,
> > +	.is_visible = arch_node_attr_is_visible,
> >  };
> >  #endif /* CONFIG_NUMA */
> >  
> > _
> 
> I'm compiling now kernel with this applied, reporting soon but the fix
> looks good to me.

Tested-by: Jarkko Sakkinen <jarkko@kernel.org>

Did two tests in a virtual machine:

1. Without the patch reproduced the crash.
2. With the patch verified that the crash does not occur.

/Jarkko