Re: [PATCH v13 2/2] x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node

[Dave Hansen <dave.hansen@intel.com>]

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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.

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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 */
 
_