linux-kernel - Re: [PATCH] [v3] x86/sgx: Fix NULL pointer dereference on non-SGX systems

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Date:   Wed, 5 Jan 2022 11:40:12 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        nathan@...nel.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
> ---
> 
>  b/arch/x86/kernel/cpu/sgx/main.c |   65 ++++++++++++++++++++++++++++-----------
>  1 file changed, 47 insertions(+), 18 deletions(-)

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>