x86: asm: make sure __put_user_size() evaluates pointer once

User access macros must ensure their arguments are evaluated only once if
they are used more than once in the macro body.  Adding
instrument_put_user() to __put_user_size() resulted in double evaluation
of the `ptr` argument, which led to correctness issues when performing
e.g.  unsafe_put_user(..., p++, ...).

To fix those issues, evaluate the `ptr` argument of __put_user_size() at
the beginning of the macro.

Link: https://lkml.kernel.org/r/20221024212144.2852069-4-glider@google.com
Fixes: 888f84a6da4d ("x86: asm: instrument usercopy in get_user() and put_user()")
Signed-off-by: Alexander Potapenko <glider@google.com>
Reported-by: youling257 <youling257@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 8bc614c..1cc756e 100644 (file)
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -254,24 +254,25 @@ extern void __put_user_nocheck_8(void);
 #define __put_user_size(x, ptr, size, label)                           \
 do {                                                                   \
        __typeof__(*(ptr)) __x = (x); /* eval x once */                 \
-       __chk_user_ptr(ptr);                                            \
+       __typeof__(ptr) __ptr = (ptr); /* eval ptr once */              \
+       __chk_user_ptr(__ptr);                                          \
        switch (size) {                                                 \
        case 1:                                                         \
-               __put_user_goto(__x, ptr, "b", "iq", label);            \
+               __put_user_goto(__x, __ptr, "b", "iq", label);          \
                break;                                                  \
        case 2:                                                         \
-               __put_user_goto(__x, ptr, "w", "ir", label);            \
+               __put_user_goto(__x, __ptr, "w", "ir", label);          \
                break;                                                  \
        case 4:                                                         \
-               __put_user_goto(__x, ptr, "l", "ir", label);            \
+               __put_user_goto(__x, __ptr, "l", "ir", label);          \
                break;                                                  \
        case 8:                                                         \
-               __put_user_goto_u64(__x, ptr, label);                   \
+               __put_user_goto_u64(__x, __ptr, label);                 \
                break;                                                  \
        default:                                                        \
                __put_user_bad();                                       \
        }                                                               \
-       instrument_put_user(__x, ptr, size);                            \
+       instrument_put_user(__x, __ptr, size);                          \
 } while (0)
 
 #ifdef CONFIG_CC_HAS_ASM_GOTO_OUTPUT