From: Robin Murphy <robin.murphy@xxxxxxx>
commit 51369e398d0d33e8f524314e672b07e8cf870e79 upstream.
Currently, USER_DS represents an exclusive limit while KERNEL_DS is
inclusive. In order to do some clever trickery for speculation-safe
masking, we need them both to behave equivalently - there aren't enough
bits to make KERNEL_DS exclusive, so we have precisely one option. This
also happens to correct a longstanding false negative for a range
ending on the very top byte of kernel memory.
Mark Rutland points out that we've actually got the semantics of
addresses vs. segments muddled up in most of the places we need to
amend, so shuffle the {USER,KERNEL}_DS definitions around such that we
can correct those properly instead of just pasting "-1"s everywhere.
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
[ 4.4: Dropped changes from fault.c and fixed minor rebase conflict ]
Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
---
arch/arm64/include/asm/processor.h | 3 ++
arch/arm64/include/asm/uaccess.h | 45 +++++++++++++++++-------------
arch/arm64/kernel/entry.S | 4 +--
3 files changed, 31 insertions(+), 21 deletions(-)
diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 75d9ef6c457c..ff1449c25bf4 100644
--- a/arch/arm64/include/asm/processor.h
+++ b/arch/arm64/include/asm/processor.h
@@ -21,6 +21,9 @@
#define TASK_SIZE_64 (UL(1) << VA_BITS)
+#define KERNEL_DS UL(-1)
+#define USER_DS (TASK_SIZE_64 - 1)
+
#ifndef __ASSEMBLY__
/*
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 829fa6d3e561..c625cc5531fc 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -56,10 +56,7 @@ struct exception_table_entry
extern int fixup_exception(struct pt_regs *regs);
-#define KERNEL_DS (-1UL)
#define get_ds() (KERNEL_DS)
-
-#define USER_DS TASK_SIZE_64
#define get_fs() (current_thread_info()->addr_limit)
static inline void set_fs(mm_segment_t fs)
@@ -87,22 +84,32 @@ static inline void set_fs(mm_segment_t fs)
* Returns 1 if the range is valid, 0 otherwise.
*
* This is equivalent to the following test:
- * (u65)addr + (u65)size <= current->addr_limit
- *
- * This needs 65-bit arithmetic.
+ * (u65)addr + (u65)size <= (u65)current->addr_limit + 1
*/
-#define __range_ok(addr, size) \
-({ \
- unsigned long __addr = (unsigned long __force)(addr); \
- unsigned long flag, roksum; \
- __chk_user_ptr(addr); \
- asm("adds %1, %1, %3; ccmp %1, %4, #2, cc; cset %0, ls" \
- : "=&r" (flag), "=&r" (roksum) \
- : "1" (__addr), "Ir" (size), \
- "r" (current_thread_info()->addr_limit) \
- : "cc"); \
- flag; \
-})
+static inline unsigned long __range_ok(unsigned long addr, unsigned long size)
+{
+ unsigned long limit = current_thread_info()->addr_limit;
+
+ __chk_user_ptr(addr);
+ asm volatile(
+ // A + B <= C + 1 for all A,B,C, in four easy steps:
+ // 1: X = A + B; X' = X % 2^64
+ " adds %0, %0, %2\n"
+ // 2: Set C = 0 if X > 2^64, to guarantee X' > C in step 4
+ " csel %1, xzr, %1, hi\n"
+ // 3: Set X' = ~0 if X >= 2^64. For X == 2^64, this decrements X'
+ // to compensate for the carry flag being set in step 4. For
+ // X > 2^64, X' merely has to remain nonzero, which it does.
+ " csinv %0, %0, xzr, cc\n"
+ // 4: For X < 2^64, this gives us X' - C - 1 <= 0, where the -1
+ // comes from the carry in being clear. Otherwise, we are
+ // testing X' - C == 0, subject to the previous adjustments.
+ " sbcs xzr, %0, %1\n"
+ " cset %0, ls\n"
+ : "+r" (addr), "+r" (limit) : "Ir" (size) : "cc");
+
+ return addr;
+}
/*
* When dealing with data aborts, watchpoints, or instruction traps we may end
@@ -111,7 +118,7 @@ static inline void set_fs(mm_segment_t fs)
*/
#define untagged_addr(addr) sign_extend64(addr, 55)
-#define access_ok(type, addr, size) __range_ok(addr, size)
+#define access_ok(type, addr, size) __range_ok((unsigned long)(addr), size)
#define user_addr_max get_fs
/*
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index c849be9231bb..4c5013b09dcb 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -96,10 +96,10 @@
.else
add x21, sp, #S_FRAME_SIZE
get_thread_info tsk
- /* Save the task's original addr_limit and set USER_DS (TASK_SIZE_64) */
+ /* Save the task's original addr_limit and set USER_DS */
ldr x20, [tsk, #TI_ADDR_LIMIT]
str x20, [sp, #S_ORIG_ADDR_LIMIT]
- mov x20, #TASK_SIZE_64
+ mov x20, #USER_DS
str x20, [tsk, #TI_ADDR_LIMIT]
.endif /* \el == 0 */
mrs x22, elr_el1
--
2.21.0.rc0.269.g1a574e7a288b
