arm64: Make USER_DS an inclusive limit

Commit 51369e398d0d 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@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
index 7dddca21fc64e28f694361bdbc05ce19be311b35..fda6f5812281c2d6f549283d4277ab04e4cb153d 100644 (file)
--- 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 335dfe02a846fece1429556038bfa6ebfe23dd5c..87a6a52cee65b057a28aca06cfb7236b4dc627fe 100644 (file)
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -35,10 +35,7 @@
 #include <asm/compiler.h>
 #include <asm/extable.h>
 
-#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)
@@ -66,22 +63,32 @@ 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)(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
@@ -90,7 +97,7 @@ 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
 
 #define _ASM_EXTABLE(from, to)                                         \

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 9766039eef31d71777c725c7932285044d46c712..206186e1f17f338d8f4e05ee0d83140020211606 100644 (file)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -167,10 +167,10 @@ alternative_else_nop_endif
        .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, #TSK_TI_ADDR_LIMIT]
        str     x20, [sp, #S_ORIG_ADDR_LIMIT]
-       mov     x20, #TASK_SIZE_64
+       mov     x20, #USER_DS
        str     x20, [tsk, #TSK_TI_ADDR_LIMIT]
        /* No need to reset PSTATE.UAO, hardware's already set it to 0 for us */
        .endif /* \el == 0 */

diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index b64958b23a7fa193c23dd1a9039f69f4e9f0b863..2789f46622864fd7f372a4646f0a08278e97ec74 100644 (file)
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -242,7 +242,7 @@ static inline bool is_permission_fault(unsigned int esr, struct pt_regs *regs,
        if (fsc_type == ESR_ELx_FSC_PERM)
                return true;
 
-       if (addr < USER_DS && system_uses_ttbr0_pan())
+       if (addr < TASK_SIZE && system_uses_ttbr0_pan())
                return fsc_type == ESR_ELx_FSC_FAULT &&
                        (regs->pstate & PSR_PAN_BIT);
 
@@ -426,7 +426,7 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr,
                mm_flags |= FAULT_FLAG_WRITE;
        }
 
-       if (addr < USER_DS && is_permission_fault(esr, regs, addr)) {
+       if (addr < TASK_SIZE && is_permission_fault(esr, regs, addr)) {
                /* regs->orig_addr_limit may be 0 if we entered from EL0 */
                if (regs->orig_addr_limit == KERNEL_DS)
                        die("Accessing user space memory with fs=KERNEL_DS", regs, esr);