linux-kernel - Re: [PATCH] wireguard: allowedips: Prevent unaligned memory accesses

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Message-ID: <ZoWUQho7noWwAqrF@zx2c4.com>
Date: Wed, 3 Jul 2024 20:11:14 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Helge Deller <deller@...nel.org>
Cc: wireguard@...ts.zx2c4.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org
Subject: Re: [PATCH] wireguard: allowedips: Prevent unaligned memory accesses

Hi Helge,

On Wed, Jul 03, 2024 at 06:20:19PM +0200, Helge Deller wrote:
> On the parisc platform the Linux kernel issues kernel warnings because
> swap_endian() tries to load a 128-bit IPv6 address from an unaligned
> memory location:
>  Kernel: unaligned access to 0x55f4688c in wg_allowedips_insert_v6+0x2c/0x80 [wireguard] (iir 0xf3010df)
>  Kernel: unaligned access to 0x55f46884 in wg_allowedips_insert_v6+0x38/0x80 [wireguard] (iir 0xf2010dc)
> 
> Avoid such unaligned memory accesses by instead using the
> get_unaligned_be64() helper macro.
> 
> Signed-off-by: Helge Deller <deller@....de>
> 
> diff --git a/drivers/net/wireguard/allowedips.c b/drivers/net/wireguard/allowedips.c
> index 0ba714ca5185..daf967130b72 100644
> --- a/drivers/net/wireguard/allowedips.c
> +++ b/drivers/net/wireguard/allowedips.c
> @@ -15,8 +15,8 @@ static void swap_endian(u8 *dst, const u8 *src, u8 bits)
>  	if (bits == 32) {
>  		*(u32 *)dst = be32_to_cpu(*(const __be32 *)src);
>  	} else if (bits == 128) {
> -		((u64 *)dst)[0] = be64_to_cpu(((const __be64 *)src)[0]);
> -		((u64 *)dst)[1] = be64_to_cpu(((const __be64 *)src)[1]);
> +		((u64 *)dst)[0] = get_unaligned_be64(src);

Ahh, right, in6_addr only has a u32 member, not a u64 member, so that's
potentially unaligned.

> +		((u64 *)dst)[1] = get_unaligned_be64(src[8]);

src[8] is not correct, however. (This crashes; did you test it?) I've
fixed it up and put it in the wireguard tree:

https://git.kernel.org/pub/scm/linux/kernel/git/zx2c4/wireguard-linux.git/commit/?id=ad3d9eef8e1b304b243e63124581f97c88ce7ff9

I'll push this up to net.git soon. Thanks for the patch.

Jason