[ARM] Fix kernel-mode undefined instruction aborts

If the kernel attempts to execute a CP1 or CP2 instruction and it
aborts, and a FP emulator is not loaded, we try to return as if to
a user context, instead of the proper kernel context.  Since the
fault came from kernel mode, we must use the kernel return paths.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 8 insertions, 4 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 2db42b18f53f..8517c3c3eb33 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -436,7 +436,7 @@ __und_usr:
         usr_entry
 
         tst     r3, #PSR_T_BIT                  @ Thumb mode?
-        bne     fpundefinstr                    @ ignore FP
+        bne     __und_usr_unknown               @ ignore FP
         sub     r4, r2, #4
 
         @
@@ -448,7 +448,7 @@ __und_usr:
         @
 1:      ldrt    r0, [r4]
         adr     r9, ret_from_exception
-        adr     lr, fpundefinstr
+        adr     lr, __und_usr_unknown
         @
         @ fallthrough to call_fpe
         @
@@ -476,7 +476,9 @@ __und_usr:
  * Emulators may wish to make use of the following registers:
  *  r0  = instruction opcode.
  *  r2  = PC+4
+ *  r9  = normal "successful" return address
  *  r10 = this threads thread_info structure.
+ *  lr  = unrecognised instruction return address
  */
 call_fpe:
         tst     r0, #0x08000000                 @ only CDP/CPRT/LDC/STC have bit 27
@@ -545,10 +547,12 @@ do_fpe:
 
         .data
 ENTRY(fp_enter)
-        .word   fpundefinstr
+        .word   no_fp
         .text
 
-fpundefinstr:
+no_fp:  mov     pc, lr
+
+__und_usr_unknown:
         mov     r0, sp
         adr     lr, ret_from_exception
         b       do_undefinstr