On Thu, Apr 02, 2020 at 07:34:19AM +0000, Christophe Leroy wrote:
> Add support for selective read or write user access with
> user_read_access_begin/end and user_write_access_begin/end.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
-Kees
> ---
> arch/powerpc/include/asm/book3s/32/kup.h | 4 ++--
> arch/powerpc/include/asm/kup.h | 14 +++++++++++++-
> arch/powerpc/include/asm/uaccess.h | 22 ++++++++++++++++++++++
> 3 files changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/32/kup.h b/arch/powerpc/include/asm/book3s/32/kup.h
> index 3c0ba22dc360..1617e73bee30 100644
> --- a/arch/powerpc/include/asm/book3s/32/kup.h
> +++ b/arch/powerpc/include/asm/book3s/32/kup.h
> @@ -108,7 +108,7 @@ static __always_inline void allow_user_access(void __user *to, const void __user
> u32 addr, end;
>
> BUILD_BUG_ON(!__builtin_constant_p(dir));
> - BUILD_BUG_ON(dir == KUAP_CURRENT);
> + BUILD_BUG_ON(dir & ~KUAP_READ_WRITE);
>
> if (!(dir & KUAP_WRITE))
> return;
> @@ -131,7 +131,7 @@ static __always_inline void prevent_user_access(void __user *to, const void __us
>
> BUILD_BUG_ON(!__builtin_constant_p(dir));
>
> - if (dir == KUAP_CURRENT) {
> + if (dir & KUAP_CURRENT_WRITE) {
> u32 kuap = current->thread.kuap;
>
> if (unlikely(!kuap))
> diff --git a/arch/powerpc/include/asm/kup.h b/arch/powerpc/include/asm/kup.h
> index 92bcd1a26d73..c745ee41ad66 100644
> --- a/arch/powerpc/include/asm/kup.h
> +++ b/arch/powerpc/include/asm/kup.h
> @@ -10,7 +10,9 @@
> * Use the current saved situation instead of the to/from/size params.
> * Used on book3s/32
> */
> -#define KUAP_CURRENT 4
> +#define KUAP_CURRENT_READ 4
> +#define KUAP_CURRENT_WRITE 8
> +#define KUAP_CURRENT (KUAP_CURRENT_READ | KUAP_CURRENT_WRITE)
>
> #ifdef CONFIG_PPC64
> #include <asm/book3s/64/kup-radix.h>
> @@ -101,6 +103,16 @@ static inline void prevent_current_access_user(void)
> prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT);
> }
>
> +static inline void prevent_current_read_from_user(void)
> +{
> + prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT_READ);
> +}
> +
> +static inline void prevent_current_write_to_user(void)
> +{
> + prevent_user_access(NULL, NULL, ~0UL, KUAP_CURRENT_WRITE);
> +}
> +
> #endif /* !__ASSEMBLY__ */
>
> #endif /* _ASM_POWERPC_KUAP_H_ */
> diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> index 2f500debae21..4427d419eb1d 100644
> --- a/arch/powerpc/include/asm/uaccess.h
> +++ b/arch/powerpc/include/asm/uaccess.h
> @@ -468,6 +468,28 @@ static __must_check inline bool user_access_begin(const void __user *ptr, size_t
> #define user_access_save prevent_user_access_return
> #define user_access_restore restore_user_access
>
> +static __must_check inline bool
> +user_read_access_begin(const void __user *ptr, size_t len)
> +{
> + if (unlikely(!access_ok(ptr, len)))
> + return false;
> + allow_read_from_user(ptr, len);
> + return true;
> +}
> +#define user_read_access_begin user_read_access_begin
> +#define user_read_access_end prevent_current_read_from_user
> +
> +static __must_check inline bool
> +user_write_access_begin(const void __user *ptr, size_t len)
> +{
> + if (unlikely(!access_ok(ptr, len)))
> + return false;
> + allow_write_to_user((void __user *)ptr, len);
> + return true;
> +}
> +#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_put_user(x, p, e) unsafe_op_wrap(__put_user_allowed(x, p), e)
> --
> 2.25.0
>
--
Kees Cook
