ARM: spectre-v1: use get_user() for __get_user()

Fixing __get_user() for spectre variant 1 is not sane: we would have to
add address space bounds checking in order to validate that the location
should be accessed, and then zero the address if found to be invalid.

Since __get_user() is supposed to avoid the bounds check, and this is
exactly what get_user() does, there's no point having two different
implementations that are doing the same thing.  So, when the Spectre
workarounds are required, make __get_user() an alias of get_user().

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 29fa6f3..4140be4 100644 (file)
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -250,6 +250,16 @@ static inline void set_fs(mm_segment_t fs)
 #define user_addr_max() \
        (uaccess_kernel() ? ~0UL : get_fs())
 
+#ifdef CONFIG_CPU_SPECTRE
+/*
+ * When mitigating Spectre variant 1, it is not worth fixing the non-
+ * verifying accessors, because we need to add verification of the
+ * address space there.  Force these to use the standard get_user()
+ * version instead.
+ */
+#define __get_user(x, ptr) get_user(x, ptr)
+#else
+
 /*
  * The "__xxx" versions of the user access functions do not verify the
  * address space - it must have been done previously with a separate
@@ -266,12 +276,6 @@ static inline void set_fs(mm_segment_t fs)
        __gu_err;                                                       \
 })
 
-#define __get_user_error(x, ptr, err)                                  \
-({                                                                     \
-       __get_user_err((x), (ptr), err);                                \
-       (void) 0;                                                       \
-})
-
 #define __get_user_err(x, ptr, err)                                    \
 do {                                                                   \
        unsigned long __gu_addr = (unsigned long)(ptr);                 \
@@ -331,6 +335,7 @@ do {                                                                        \
 
 #define __get_user_asm_word(x, addr, err)                      \
        __get_user_asm(x, addr, err, ldr)
+#endif
 
 
 #define __put_user_switch(x, ptr, __err, __fn)                         \