[PATCH 4.9 07/16] ARM: 8796/1: spectre-v1,v1.1: provide helpers for address sanitization

David Long
2019-02-14T14:50:56Z

From: Julien Thierry <julien.thierry@arm.com>

Commit afaf6838f4bc896a711180b702b388b8cfa638fc upstream.

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>
Signed-off-by: David A. Long <dave.long@linaro.org>
---
arch/arm/include/asm/assembler.h | 11 +++++++++++
arch/arm/include/asm/uaccess.h | 26 ++++++++++++++++++++++++++
arch/arm/lib/copy_from_user.S | 6 +-----
3 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
index e616f61f859d..7d727506096f 100644
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -465,6 +465,17 @@ 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 b61acd62cffb..0f6c6b873bc5 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -129,6 +129,32 @@ 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 a826df3d3814..6709a8d33963 100644
--- 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"
--
2.17.1