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.le...@csgroup.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.le...@csgroup.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)


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