ARM: 8796/1: spectre-v1,v1.1: provide helpers for address sanitization

Introduce C and asm helpers to sanitize user address, taking the
address range they target into account.

Use asm helper for existing sanitization in __copy_from_user().

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index f0515f6..39651c1 100644 (file)
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -467,6 +467,17 @@ THUMB(     orr     \reg , \reg , #PSR_T_BIT        )
 #endif
        .endm
 
+       .macro uaccess_mask_range_ptr, addr:req, size:req, limit:req, tmp:req
+#ifdef CONFIG_CPU_SPECTRE
+       sub     \tmp, \limit, #1
+       subs    \tmp, \tmp, \addr       @ tmp = limit - 1 - addr
+       addhs   \tmp, \tmp, #1          @ if (tmp >= 0) {
+       subhss  \tmp, \tmp, \size       @ tmp = limit - (addr + size) }
+       movlo   \addr, #0               @ if (tmp < 0) addr = NULL
+       csdb
+#endif
+       .endm
+
        .macro  uaccess_disable, tmp, isb=1
 #ifdef CONFIG_CPU_SW_DOMAIN_PAN
        /*

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index cf50b03..a5807b6 100644 (file)
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -99,6 +99,32 @@ static inline void set_fs(mm_segment_t fs)
 #define __inttype(x) \
        __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
 
+/*
+ * Sanitise a uaccess pointer such that it becomes NULL if addr+size
+ * is above the current addr_limit.
+ */
+#define uaccess_mask_range_ptr(ptr, size)                      \
+       ((__typeof__(ptr))__uaccess_mask_range_ptr(ptr, size))
+static inline void __user *__uaccess_mask_range_ptr(const void __user *ptr,
+                                                   size_t size)
+{
+       void __user *safe_ptr = (void __user *)ptr;
+       unsigned long tmp;
+
+       asm volatile(
+       "       sub     %1, %3, #1\n"
+       "       subs    %1, %1, %0\n"
+       "       addhs   %1, %1, #1\n"
+       "       subhss  %1, %1, %2\n"
+       "       movlo   %0, #0\n"
+       : "+r" (safe_ptr), "=&r" (tmp)
+       : "r" (size), "r" (current_thread_info()->addr_limit)
+       : "cc");
+
+       csdb();
+       return safe_ptr;
+}
+
 /*
  * Single-value transfer routines.  They automatically use the right
  * size if we just have the right pointer type.  Note that the functions

diff --git a/arch/arm/lib/copy_from_user.S b/arch/arm/lib/copy_from_user.S
index a826df3..6709a8d 100644 (file)
--- a/arch/arm/lib/copy_from_user.S
+++ b/arch/arm/lib/copy_from_user.S
@@ -93,11 +93,7 @@ ENTRY(arm_copy_from_user)
 #ifdef CONFIG_CPU_SPECTRE
        get_thread_info r3
        ldr     r3, [r3, #TI_ADDR_LIMIT]
-       adds    ip, r1, r2      @ ip=addr+size
-       sub     r3, r3, #1      @ addr_limit - 1
-       cmpcc   ip, r3          @ if (addr+size > addr_limit - 1)
-       movcs   r1, #0          @ addr = NULL
-       csdb
+       uaccess_mask_range_ptr r1, r2, r3, ip
 #endif
 
 #include "copy_template.S"