linux-kernel - Re: [PATCH 2/2] x86/amd_node: fix null pointer dereference if amd_smn

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Message-ID: <20251203205427.GB741246@yaz-khff2.amd.com>
Date: Wed, 3 Dec 2025 15:54:27 -0500
From: Yazen Ghannam <yazen.ghannam@....com>
To: Steven Noonan <steven@...inklabs.net>
Cc: linux-kernel@...r.kernel.org, Ariadne Conill <ariadne@...adne.space>,
	x86@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/amd_node: fix null pointer dereference if
 amd_smn_init failed

On Fri, Nov 14, 2025 at 07:57:46PM +0000, Steven Noonan wrote:
> We should be checking the `smn_exclusive` flag before anything else,
> because that indicates whether we got through `amd_smn_init`
> successfully.
> 
> Without this change, we dereference `amd_roots` even though it may not
> be allocated.
> 
> Signed-off-by: Steven Noonan <steven@...inklabs.net>
> Signed-off-by: Ariadne Conill <ariadne@...adne.space>
> CC: Yazen Ghannam <yazen.ghannam@....com>
> CC: x86@...r.kernel.org
> CC: stable@...r.kernel.org

Same feedback here as for patch 1.

> ---
>  arch/x86/kernel/amd_node.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/amd_node.c b/arch/x86/kernel/amd_node.c
> index cdc6ba224d4ad..919932339f4a2 100644
> --- a/arch/x86/kernel/amd_node.c
> +++ b/arch/x86/kernel/amd_node.c
> @@ -88,6 +88,9 @@ static int __amd_smn_rw(u8 i_off, u8 d_off, u16 node, u32 address, u32 *value, b
>  	struct pci_dev *root;
>  	int err = -ENODEV;
>  
> +	if (!smn_exclusive)
> +		return err;
> +
>  	if (node >= amd_num_nodes())
>  		return err;
>  
> @@ -95,9 +98,6 @@ static int __amd_s
> mn_rw(u8 i_off, u8 d_off, u16 node, u32 address, u32 *value, b
>  	if (!root)
>  		return err;
>  
> -	if (!smn_exclusive)
> -		return err;
> -
>  	guard(mutex)(&smn_mutex);
>  
>  	err = pci_write_config_dword(root, i_off, address);
> -- 

This change looks good.

Did you encounter a NULL pointer dereference? Or did you find this by
code inspection?

Thanks,
Yazen