linux-kernel - Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of access

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Date:   Wed, 29 Mar 2023 17:22:49 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Gregory Price <gourry.memverge@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        oleg@...hat.com, avagin@...il.com, peterz@...radead.org,
        luto@...nel.org, krisman@...labora.com, tglx@...utronix.de,
        corbet@....net, shuah@...nel.org, arnd@...db.de, will@...nel.org,
        mark.rutland@....com, tongtiangen@...wei.com, robin.murphy@....com,
        Gregory Price <gregory.price@...verge.com>
Subject: Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of
 access_ok

On Tue, Mar 28, 2023 at 12:48:08PM -0400, Gregory Price wrote:
> diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
> index 5c7b2f9d5913..1a51a54f264f 100644
> --- a/arch/arm64/include/asm/uaccess.h
> +++ b/arch/arm64/include/asm/uaccess.h
> @@ -35,7 +35,9 @@ static inline int __access_ok(const void __user *ptr, unsigned long size);
>   * This is equivalent to the following test:
>   * (u65)addr + (u65)size <= (u65)TASK_SIZE_MAX
>   */
> -static inline int access_ok(const void __user *addr, unsigned long size)
> +static inline int task_access_ok(struct task_struct *task,
> +				 const void __user *addr,
> +				 unsigned long size)
>  {
>  	/*
>  	 * Asynchronous I/O running in a kernel thread does not have the
> @@ -43,11 +45,18 @@ static inline int access_ok(const void __user *addr, unsigned long size)
>  	 * the user address before checking.
>  	 */
>  	if (IS_ENABLED(CONFIG_ARM64_TAGGED_ADDR_ABI) &&
> -	    (current->flags & PF_KTHREAD || test_thread_flag(TIF_TAGGED_ADDR)))
> +	    (task->flags & PF_KTHREAD || test_ti_thread_flag(task, TIF_TAGGED_ADDR)))
>  		addr = untagged_addr(addr);
>  
>  	return likely(__access_ok(addr, size));
>  }
> +
> +static inline int access_ok(const void __user *addr, unsigned long size)
> +{
> +	return task_access_ok(current, addr, size);
> +}
> +
> +#define task_access_ok task_access_ok

I'd not bother with this at all. In the generic code you can either do
an __access_ok() check directly or just
access_ok(untagged_addr(selector), ...) with a comment that address
tagging of the ptraced task may not be enabled.

-- 
Catalin