linux-kernel - RE: [PATCH 2/2] x86: fix _

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Date:   Mon, 1 Apr 2019 14:37:23 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Jann Horn' <jannh@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Signed-off-by : Qiaowei Ren" <qiaowei.ren@...el.com>
Subject: RE: [PATCH 2/2] x86: fix __user annotations

From: Jann Horn
> Sent: 28 March 2019 21:23
> Fix __user annotations in various places across the x86 tree:
> 
...
>  - generic_load_microcode() deals with a pointer that can be either a
>    kernel pointer or a user pointer; change the code to pass it around as
>    a __user pointer, and add explicit casts to convert between __user and
>    __kernel
...
> -static int get_ucode_fw(void *to, const void *from, size_t n)
> +static int get_ucode_fw(void *to, const void __user *from, size_t n)
>  {
> -	memcpy(to, from, n);
> +	/* cast paired with request_microcode_fw() */
> +	memcpy(to, (const void __force *)from, n);
>  	return 0;
>  }
> 
> @@ -993,7 +996,8 @@ static enum ucode_state request_microcode_fw(int cpu, struct device *device,
>  		return UCODE_NFOUND;
>  	}
> 
> -	ret = generic_load_microcode(cpu, (void *)firmware->data,
> +	/* cast paired with get_ucode_fw() */
> +	ret = generic_load_microcode(cpu, (void __force __user *)firmware->data,
>  				     firmware->size, &get_ucode_fw);
> 
>  	release_firmware(firmware);
> @@ -1001,7 +1005,7 @@ static enum ucode_state request_microcode_fw(int cpu, struct device *device,
>  	return ret;
>  }
> 
> -static int get_ucode_user(void *to, const void *from, size_t n)
> +static int get_ucode_user(void *to, const void __user *from, size_t n)
>  {
>  	return copy_from_user(to, from, n);
>  }
> @@ -1012,7 +1016,7 @@ request_microcode_user(int cpu, const void __user *buf, size_t size)
>  	if (is_blacklisted(cpu))
>  		return UCODE_NFOUND;
> 
> -	return generic_load_microcode(cpu, (void *)buf, size, &get_ucode_user);
> +	return generic_load_microcode(cpu, buf, size, &get_ucode_user);

That is all an 'accident waiting to happen' ...

	David

-
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