linux-kernel - Re: [PATCH v1 01/15] powerpc/uaccess: Remove __get_user_allowed() and unsafe_op

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Message-ID: <87im6ao7ld.fsf@dja-thinkpad.axtens.net>
Date:   Tue, 02 Mar 2021 09:02:54 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 01/15] powerpc/uaccess: Remove __get_user_allowed() and unsafe_op_wrap()



Christophe Leroy <christophe.leroy@...roup.eu> writes:

> Those two macros have only one user which is unsafe_get_user().
>
> Put everything in one place and remove them.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
> ---
>  arch/powerpc/include/asm/uaccess.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index 78e2a3990eab..8cbf3e3874f1 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -53,9 +53,6 @@ static inline bool __access_ok(unsigned long addr, unsigned long size)
>  #define __put_user(x, ptr) \
>  	__put_user_nocheck((__typeof__(*(ptr)))(x), (ptr), sizeof(*(ptr)))
>  
> -#define __get_user_allowed(x, ptr) \
> -	__get_user_nocheck((x), (ptr), sizeof(*(ptr)), false)
> -
>  #define __get_user_inatomic(x, ptr) \
>  	__get_user_nosleep((x), (ptr), sizeof(*(ptr)))
>  #define __put_user_inatomic(x, ptr) \
> @@ -482,8 +479,11 @@ user_write_access_begin(const void __user *ptr, size_t len)
>  #define user_write_access_begin	user_write_access_begin
>  #define user_write_access_end		prevent_current_write_to_user
>  
> -#define unsafe_op_wrap(op, err) do { if (unlikely(op)) goto err; } while (0)
> -#define unsafe_get_user(x, p, e) unsafe_op_wrap(__get_user_allowed(x, p), e)
> +#define unsafe_get_user(x, p, e) do {					\
> +	if (unlikely(__get_user_nocheck((x), (p), sizeof(*(p)), false)))\
> +		goto e;							\
> +} while (0)
> +

This seems correct to me.

Checkpatch does have one check that is relevant:

CHECK: Macro argument reuse 'p' - possible side-effects?
#36: FILE: arch/powerpc/include/asm/uaccess.h:482:
+#define unsafe_get_user(x, p, e) do {					\
+	if (unlikely(__get_user_nocheck((x), (p), sizeof(*(p)), false)))\
+		goto e;							\
+} while (0)

Given that we are already creating a new block, should we do something
like this (completely untested):

#define unsafe_get_user(x, p, e) do {					\
        __typeof__(p) __p = (p);
	if (unlikely(__get_user_nocheck((x), (__p), sizeof(*(__p)), false)))\
		goto e;							\
} while (0)

Kind regards,
Daniel

>  #define unsafe_put_user(x, p, e) \
>  	__unsafe_put_user_goto((__typeof__(*(p)))(x), (p), sizeof(*(p)), e)
>  
> -- 
> 2.25.0