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Date: Tue, 4 Jan 2022 12:19:20 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
gregkh@...uxfoundation.org, jarkko@...nel.org,
linux-sgx@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] [v3] x86/sgx: Fix NULL pointer dereference on non-SGX
systems
On Tue, Jan 04, 2022 at 09:15:27AM -0800, Dave Hansen wrote:
>
> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> == Problem ==
>
> 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.
>
> == Solution ==
>
> To fix this, hide the entire nodeX/x86/ attribute group on
> systems without SGX support using the ->is_visible attribute
> group callback.
>
> Unfortunately, SGX is initialized via a device_initcall() which
> occurs _after_ the ->is_visible() callback. Instead of moving
> SGX initialization earlier, call sysfs_update_group() during
> SGX initialization to update the group visiblility.
>
> This update requires moving the SGX sysfs code earlier in
> sgx/main.c. There are no code changes other than the addition of
> arch_update_sysfs_visibility() and a minor whitespace fixup to
> arch_node_attr_is_visible() which checkpatch caught.
>
> Fixes: 50468e431335 ("x86/sgx: Add an attribute for the amount of SGX memory in a NUMA node")
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> CC: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Jarkko Sakkinen <jarkko@...nel.org>
> Cc: linux-sgx@...r.kernel.org
> Cc: x86@...nel.org
Tested-by: Nathan Chancellor <nathan@...nel.org>
> ---
>
> b/arch/x86/kernel/cpu/sgx/main.c | 65 ++++++++++++++++++++++++++++-----------
> 1 file changed, 47 insertions(+), 18 deletions(-)
>
> 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 2022-01-04 08:43:17.042821249 -0800
> @@ -6,11 +6,13 @@
> #include <linux/highmem.h>
> #include <linux/kthread.h>
> #include <linux/miscdevice.h>
> +#include <linux/node.h>
> #include <linux/pagemap.h>
> #include <linux/ratelimit.h>
> #include <linux/sched/mm.h>
> #include <linux/sched/signal.h>
> #include <linux/slab.h>
> +#include <linux/sysfs.h>
> #include <asm/sgx.h>
> #include "driver.h"
> #include "encl.h"
> @@ -780,6 +782,48 @@ static inline u64 __init sgx_calc_sectio
> ((high & GENMASK_ULL(19, 0)) << 32);
> }
>
> +#ifdef CONFIG_NUMA
> +static ssize_t sgx_total_bytes_show(struct device *dev, struct device_attribute *attr, char *buf)
> +{
> + return sysfs_emit(buf, "%lu\n", sgx_numa_nodes[dev->id].size);
> +}
> +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,
> +};
> +
> +const struct attribute_group arch_node_dev_group = {
> + .name = "x86",
> + .attrs = arch_node_dev_attrs,
> + .is_visible = arch_node_attr_is_visible,
> +};
> +
> +static void __init arch_update_sysfs_visibility(int nid)
> +{
> + struct node *node = node_devices[nid];
> + int ret;
> +
> + ret = sysfs_update_group(&node->dev.kobj, &arch_node_dev_group);
> +
> + if (ret)
> + pr_err("sysfs update failed (%d), files may be invisible", ret);
> +}
> +#else /* !CONFIG_NUMA */
> +static void __init arch_update_sysfs_visibility(int nid) {}
> +#endif
> +
> static bool __init sgx_page_cache_init(void)
> {
> u32 eax, ebx, ecx, edx, type;
> @@ -826,6 +870,9 @@ static bool __init sgx_page_cache_init(v
> INIT_LIST_HEAD(&sgx_numa_nodes[nid].sgx_poison_page_list);
> node_set(nid, sgx_numa_mask);
> sgx_numa_nodes[nid].size = 0;
> +
> + /* Make SGX-specific node sysfs files visible: */
> + arch_update_sysfs_visibility(nid);
> }
>
> sgx_epc_sections[i].node = &sgx_numa_nodes[nid];
> @@ -903,24 +950,6 @@ int sgx_set_attribute(unsigned long *all
> }
> EXPORT_SYMBOL_GPL(sgx_set_attribute);
>
> -#ifdef CONFIG_NUMA
> -static ssize_t sgx_total_bytes_show(struct device *dev, struct device_attribute *attr, char *buf)
> -{
> - return sysfs_emit(buf, "%lu\n", sgx_numa_nodes[dev->id].size);
> -}
> -static DEVICE_ATTR_RO(sgx_total_bytes);
> -
> -static struct attribute *arch_node_dev_attrs[] = {
> - &dev_attr_sgx_total_bytes.attr,
> - NULL,
> -};
> -
> -const struct attribute_group arch_node_dev_group = {
> - .name = "x86",
> - .attrs = arch_node_dev_attrs,
> -};
> -#endif /* CONFIG_NUMA */
> -
> static int __init sgx_init(void)
> {
> int ret;
> _
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