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[4.4,17/18] ARM: spectre-v1: use get_user() for __get_user()

Message ID 20181031140436.2964-18-dave.long@linaro.org
State Superseded
Headers show
Series V4.4 backport of 32-bit arm spectre patches | expand

Commit Message

David Long Oct. 31, 2018, 2:04 p.m. UTC 
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>

---
 arch/arm/include/asm/uaccess.h | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

-- 
2.17.1
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Patch

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 968b50063431..ecd159b45f12 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -314,6 +314,15 @@  static inline void set_fs(mm_segment_t fs)
 #define user_addr_max() \
 	(segment_eq(get_fs(), KERNEL_DS) ? ~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
@@ -330,12 +339,6 @@  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);			\
@@ -395,6 +398,7 @@  do {									\
 
 #define __get_user_asm_word(x, addr, err)			\
 	__get_user_asm(x, addr, err, ldr)
+#endif
 
 #define __put_user(x, ptr)						\
 ({									\