releases/4.9.30/powerpc-64e-fix-hang-when-debugging-programs-with-relocated-kernel.patch

   1 From fd615f69a18a9d4aa5ef02a1dc83f319f75da8e7 Mon Sep 17 00:00:00 2001
   2 From: LiuHailong <liu.hailong6@zte.com.cn>
   3 Date: Tue, 7 Feb 2017 10:35:52 +0800
   4 Subject: powerpc/64e: Fix hang when debugging programs with relocated kernel
   5
   6 From: LiuHailong <liu.hailong6@zte.com.cn>
   7
   8 commit fd615f69a18a9d4aa5ef02a1dc83f319f75da8e7 upstream.
   9
  10 Debug interrupts can be taken during interrupt entry, since interrupt
  11 entry does not automatically turn them off.  The kernel will check
  12 whether the faulting instruction is between [interrupt_base_book3e,
  13 __end_interrupts], and if so clear MSR[DE] and return.
  14
  15 However, when the kernel is built with CONFIG_RELOCATABLE, it can't use
  16 LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e) and
  17 LOAD_REG_IMMEDIATE(r15,__end_interrupts), as they ignore relocation.
  18 Thus, if the kernel is actually running at a different address than it
  19 was built at, the address comparison will fail, and the exception entry
  20 code will hang at kernel_dbg_exc.
  21
  22 r2(toc) is also not usable here, as r2 still holds data from the
  23 interrupted context, so LOAD_REG_ADDR() doesn't work either.  So we use
  24 the *name@got* to get the EV of two labels directly.
  25
  26 Test programs test.c shows as follows:
  27 int main(int argc, char *argv[])
  28 {
  29         if (access("/proc/sys/kernel/perf_event_paranoid", F_OK) == -1)
  30                 printf("Kernel doesn't have perf_event support\n");
  31 }
  32
  33 Steps to reproduce the bug, for example:
  34  1) ./gdb ./test
  35  2) (gdb) b access
  36  3) (gdb) r
  37  4) (gdb) s
  38
  39 Signed-off-by: Liu Hailong <liu.hailong6@zte.com.cn>
  40 Signed-off-by: Jiang Xuexin <jiang.xuexin@zte.com.cn>
  41 Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
  42 Reviewed-by: Liu Song <liu.song11@zte.com.cn>
  43 Reviewed-by: Huang Jian <huang.jian@zte.com.cn>
  44 [scottwood: cleaned up commit message, and specified bad behavior
  45  as a hang rather than an oops to correspond to mainline kernel behavior]
  46 Fixes: 1cb6e0649248 ("powerpc/book3e: support CONFIG_RELOCATABLE")
  47 Signed-off-by: Scott Wood <oss@buserror.net>
  48 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  49
  50 ---
  51  arch/powerpc/kernel/exceptions-64e.S |   12 ++++++++++++
  52  1 file changed, 12 insertions(+)
  53
  54 --- a/arch/powerpc/kernel/exceptions-64e.S
  55 +++ b/arch/powerpc/kernel/exceptions-64e.S
  56 @@ -735,8 +735,14 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
  57         andis.  r15,r14,(DBSR_IC|DBSR_BT)@h
  58         beq+    1f
  59
  60 +#ifdef CONFIG_RELOCATABLE
  61 +       ld      r15,PACATOC(r13)
  62 +       ld      r14,interrupt_base_book3e@got(r15)
  63 +       ld      r15,__end_interrupts@got(r15)
  64 +#else
  65         LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e)
  66         LOAD_REG_IMMEDIATE(r15,__end_interrupts)
  67 +#endif
  68         cmpld   cr0,r10,r14
  69         cmpld   cr1,r10,r15
  70         blt+    cr0,1f
  71 @@ -799,8 +805,14 @@ kernel_dbg_exc:
  72         andis.  r15,r14,(DBSR_IC|DBSR_BT)@h
  73         beq+    1f
  74
  75 +#ifdef CONFIG_RELOCATABLE
  76 +       ld      r15,PACATOC(r13)
  77 +       ld      r14,interrupt_base_book3e@got(r15)
  78 +       ld      r15,__end_interrupts@got(r15)
  79 +#else
  80         LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e)
  81         LOAD_REG_IMMEDIATE(r15,__end_interrupts)
  82 +#endif
  83         cmpld   cr0,r10,r14
  84         cmpld   cr1,r10,r15
  85         blt+    cr0,1f