xtensa: don't allow overflow/underflow on unaligned stack

Double exceptions that happen during register window overflow/underflow
are handled in the topmost stack frame, as if it was the only exception
that occured. However unaligned access exception handler is special
because it needs to analyze instruction that caused the exception, but
the userspace instruction that triggered window exception is completely
irrelevant. Unaligned data access is rather normal in the generic
userspace code, but stack pointer manipulation must always be done by
architecture-aware code and thus unaligned stack means a serious problem
anyway.
Use the default unaligned access handler that raises SIGBUS in case
of unaligned access in window overflow/underflow handler.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

3 files changed, 10 insertions, 7 deletions

diff --git a/arch/xtensa/kernel/traps.c b/arch/xtensa/kernel/traps.c
index eebbfd8c26fc..9d2f45f010ef 100644
--- a/arch/xtensa/kernel/traps.c
+++ b/arch/xtensa/kernel/traps.c
@@ -101,9 +101,8 @@ static dispatch_init_table_t __initdata dispatch_init_table[] = {
 #if XCHAL_UNALIGNED_LOAD_EXCEPTION || XCHAL_UNALIGNED_STORE_EXCEPTION
 #ifdef CONFIG_XTENSA_UNALIGNED_USER
 { EXCCAUSE_UNALIGNED,           USER,      fast_unaligned },
-#else
-{ EXCCAUSE_UNALIGNED,           0,         do_unaligned_user },
 #endif
+{ EXCCAUSE_UNALIGNED,           0,         do_unaligned_user },
 { EXCCAUSE_UNALIGNED,           KRNL,      fast_unaligned },
 #endif
 #ifdef CONFIG_MMU
@@ -264,7 +263,6 @@ do_illegal_instruction(struct pt_regs *regs)
  */
 
 #if XCHAL_UNALIGNED_LOAD_EXCEPTION || XCHAL_UNALIGNED_STORE_EXCEPTION
-#ifndef CONFIG_XTENSA_UNALIGNED_USER
 void
 do_unaligned_user (struct pt_regs *regs)
 {
@@ -286,7 +284,6 @@ do_unaligned_user (struct pt_regs *regs)
 
 }
 #endif
-#endif
 
 void
 do_debug(struct pt_regs *regs)
diff --git a/arch/xtensa/kernel/vectors.S b/arch/xtensa/kernel/vectors.S
index 8453e6e39895..1b397a902292 100644
--- a/arch/xtensa/kernel/vectors.S
+++ b/arch/xtensa/kernel/vectors.S
@@ -454,8 +454,14 @@ _DoubleExceptionVector_WindowOverflow:
         s32i    a0, a2, PT_DEPC
 
 _DoubleExceptionVector_handle_exception:
+        addi    a0, a0, -EXCCAUSE_UNALIGNED
+        beqz    a0, 2f
         addx4   a0, a0, a3
-        l32i    a0, a0, EXC_TABLE_FAST_USER
+        l32i    a0, a0, EXC_TABLE_FAST_USER + 4 * EXCCAUSE_UNALIGNED
+        xsr     a3, excsave1
+        jx      a0
+2:
+        movi    a0, user_exception
         xsr     a3, excsave1
         jx      a0
 
diff --git a/arch/xtensa/kernel/vmlinux.lds.S b/arch/xtensa/kernel/vmlinux.lds.S
index d16db6df86f8..fc1bc2ba8d5d 100644
--- a/arch/xtensa/kernel/vmlinux.lds.S
+++ b/arch/xtensa/kernel/vmlinux.lds.S
@@ -269,13 +269,13 @@ SECTIONS
                   .UserExceptionVector.literal)
   SECTION_VECTOR (_DoubleExceptionVector_literal,
                   .DoubleExceptionVector.literal,
-                  DOUBLEEXC_VECTOR_VADDR - 40,
+                  DOUBLEEXC_VECTOR_VADDR - 48,
                   SIZEOF(.UserExceptionVector.text),
                   .UserExceptionVector.text)
   SECTION_VECTOR (_DoubleExceptionVector_text,
                   .DoubleExceptionVector.text,
                   DOUBLEEXC_VECTOR_VADDR,
-                  40,
+                  48,
                   .DoubleExceptionVector.literal)
 
   . = (LOADADDR( .DoubleExceptionVector.text ) + SIZEOF( .DoubleExceptionVector.text ) + 3) & ~ 3;