[PATCH 4.14 107/109] ARM: spectre-v1: use get_user() for __get_user()

Greg Kroah-Hartman
2018-10-16T17:22:11Z

From: Russell King <rmk+kernel@armlinux.org.uk>

Commit b1cd0a14806321721aae45f5446ed83a3647c914 upstream.

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>
Signed-off-by: David A. Long <dave.long@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm/include/asm/uaccess.h | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

--- 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 f
#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 f
__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) \