Re: [PATCH v1 01/15] powerpc/uaccess: Remove __get_user_allowed() and unsafe_op_wrap()

[Christophe Leroy]

Le 01/03/2021 à 23:02, Daniel Axtens a écrit :
> Christophe Leroy <christophe.leroy@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> >   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)

As mentioned by Segher, this is not needed, sizeof(p) doesn't evaluate (p) so (p) is only evaluated 
once in the macro, so no risk of side-effects with that.

Christophe