linux-kernel - Re: [PATCH] riscv: misaligned: Restrict user access to kernel memory

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Message-ID: <384451e5-e2af-44f7-a5b5-894049232e09@ghiti.fr>
Date: Thu, 15 Aug 2024 11:29:01 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Samuel Holland <samuel.holland@...ive.com>,
 Palmer Dabbelt <palmer@...belt.com>
Cc: stable@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
 Ben Dooks <ben.dooks@...ethink.co.uk>, Björn Töpel
 <bjorn@...osinc.com>, Charlie Jenkins <charlie@...osinc.com>,
 Clément Léger <cleger@...osinc.com>,
 Conor Dooley <conor.dooley@...rochip.com>, Evan Green <evan@...osinc.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, linux-kernel@...r.kernel.org,
 linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] riscv: misaligned: Restrict user access to kernel memory

Hi Samuel,

On 15/08/2024 02:57, Samuel Holland wrote:
> raw_copy_{to,from}_user() do not call access_ok(), so this code allowed
> userspace to access any virtual memory address.
>
> Cc: stable@...r.kernel.org
> Fixes: 7c83232161f6 ("riscv: add support for misaligned trap handling in S-mode")
> Fixes: 441381506ba7 ("riscv: misaligned: remove CONFIG_RISCV_M_MODE specific code")
> Signed-off-by: Samuel Holland <samuel.holland@...ive.com>
> ---
>
>   arch/riscv/kernel/traps_misaligned.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index b62d5a2f4541..1a76f99ff185 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -417,7 +417,7 @@ int handle_misaligned_load(struct pt_regs *regs)
>   
>   	val.data_u64 = 0;
>   	if (user_mode(regs)) {
> -		if (raw_copy_from_user(&val, (u8 __user *)addr, len))
> +		if (copy_from_user(&val, (u8 __user *)addr, len))
>   			return -1;
>   	} else {
>   		memcpy(&val, (u8 *)addr, len);
> @@ -515,7 +515,7 @@ int handle_misaligned_store(struct pt_regs *regs)
>   		return -EOPNOTSUPP;
>   
>   	if (user_mode(regs)) {
> -		if (raw_copy_to_user((u8 __user *)addr, &val, len))
> +		if (copy_to_user((u8 __user *)addr, &val, len))
>   			return -1;
>   	} else {
>   		memcpy((u8 *)addr, &val, len);


We could even do the access_ok() *before* even calling 
handle_misaligned_load() in do_trap_load_misaligned() to back off 
earlier. But unless you think it is important, I'm fine with this patch, 
it's on my list for -fixes!

Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>

Thanks,

Alex