[PATCH 1/4] powerpc/64s: implement probe_kernel_read/write without touching AMR

[Christophe Leroy]

Le 27/03/2020 à 08:02, Nicholas Piggin a écrit :
> There is no need to allow user accesses when probing kernel addresses.
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
> ---
>   arch/powerpc/include/asm/uaccess.h | 25 ++++++++++-----
>   arch/powerpc/lib/Makefile          |  2 +-
>   arch/powerpc/lib/uaccess.c         | 50 ++++++++++++++++++++++++++++++
>   3 files changed, 68 insertions(+), 9 deletions(-)
>   create mode 100644 arch/powerpc/lib/uaccess.c
> 

[...]

> diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
> index b8de3be10eb4..a15060b5008e 100644
> --- a/arch/powerpc/lib/Makefile
> +++ b/arch/powerpc/lib/Makefile
> @@ -36,7 +36,7 @@ extra-$(CONFIG_PPC64)	+= crtsavres.o
>   endif
>   
>   obj-$(CONFIG_PPC_BOOK3S_64) += copyuser_power7.o copypage_power7.o \
> -			       memcpy_power7.o
> +			       memcpy_power7.o uaccess.o

Why only book3s/64 ? It applies to the 8xx and book3s/32 as well, I 
think it should just be for all powerpc.

>   
>   obj64-y	+= copypage_64.o copyuser_64.o mem_64.o hweight_64.o \
>   	   memcpy_64.o memcpy_mcsafe_64.o
> diff --git a/arch/powerpc/lib/uaccess.c b/arch/powerpc/lib/uaccess.c
> new file mode 100644
> index 000000000000..0057ab52d6fe
> --- /dev/null
> +++ b/arch/powerpc/lib/uaccess.c
> @@ -0,0 +1,50 @@
> +#include <linux/mm.h>
> +#include <linux/uaccess.h>
> +
> +static __always_inline long
> +probe_read_common(void *dst, const void __user *src, size_t size)
> +{
> +	long ret;
> +
> +	pagefault_disable();
> +	ret = raw_copy_from_user_allowed(dst, src, size);
> +	pagefault_enable();
> +
> +	return ret ? -EFAULT : 0;
> +}
> +
> +static __always_inline long
> +probe_write_common(void __user *dst, const void *src, size_t size)
> +{
> +	long ret;
> +
> +	pagefault_disable();
> +	ret = raw_copy_to_user_allowed(dst, src, size);
> +	pagefault_enable();
> +
> +	return ret ? -EFAULT : 0;
> +}
> +
> +long probe_kernel_read(void *dst, const void *src, size_t size)
> +{
> +	long ret;
> +	mm_segment_t old_fs = get_fs();
> +
> +	set_fs(KERNEL_DS);
> +	ret = probe_read_common(dst, (__force const void __user *)src, size);

I think you should squash probe_read_common() here, having it separated 
is a lot of lines for no added value. It also may make people believe it 
overwrites the generic probe_read_common()


> +	set_fs(old_fs);
> +
> +	return ret;
> +}
> +
> +long probe_kernel_write(void *dst, const void *src, size_t size)
> +{
> +	long ret;
> +	mm_segment_t old_fs = get_fs();
> +
> +	set_fs(KERNEL_DS);
> +	ret = probe_write_common((__force void __user *)dst, src, size);

Same comment as for probe_read_common()

> +	set_fs(old_fs);
> +
> +	return ret;
> +}
> 

Christophe