[PATCH 1/2] Revert "powerpc64/elfv1: Only dereference function descriptor for non-text symbols"

[Naveen N. Rao]

This reverts commit 83e840c770f2c5 ("powerpc64/elfv1: Only dereference
function descriptor for non-text symbols").

Chandan reported that on newer kernels, trying to enable function_graph
tracer on ppc64 (BE) locks up the system with the following trace:

  Unable to handle kernel paging request for data at address 0x600000002fa30010
  Faulting instruction address: 0xc0000000001f1300
  Thread overran stack, or stack corrupted
  Oops: Kernel access of bad area, sig: 11 [#1]
  BE SMP NR_CPUS=2048 DEBUG_PAGEALLOC NUMA pSeries
  Modules linked in:
  CPU: 1 PID: 6586 Comm: bash Not tainted 4.14.0-rc3-00162-g6e51f1f-dirty #20
  task: c000000625c07200 task.stack: c000000625c07310
  NIP:  c0000000001f1300 LR: c000000000121cac CTR: c000000000061af8
  REGS: c000000625c088c0 TRAP: 0380   Not tainted  (4.14.0-rc3-00162-g6e51f1f-dirty)
  MSR:  8000000000001032 <SF,ME,IR,DR,RI>  CR: 28002848  XER: 00000000
  CFAR: c0000000001f1320 SOFTE: 0
  GPR00: c000000000121cac c000000625c08b40 c000000001439700 c00000000125c5a8
  GPR04: c0000000013a0040 c00000000135cbf0 0000000000000000 0000000000000000
  GPR08: e92d0250812a1a30 e92d025081291a30 600000002fa30000 c000000625c08c50
  GPR12: 0000000028002842 c00000000fd40580 000000010bacae64 ffffffffffffffff
  GPR16: 000000010bac96c8 0000000000000000 0000000000000000 0000000000000000
  GPR20: 0000000000000000 0000000000000000 000000010bac0734 000000000000000a
  GPR24: 0000000000000000 c000000636cd6610 c000000113258b80 0000000000000000
  GPR28: c000000000061b10 c000000000061960 c00000000125c5d8 c0000000013a0040
  NIP [c0000000001f1300] .__is_insn_slot_addr+0x30/0x90
  LR [c000000000121cac] .kernel_text_address+0x18c/0x1c0
  Call Trace:
  [c000000625c08b40] [c0000000001bd040] .is_module_text_address+0x20/0x40 (unreliable)
  [c000000625c08bc0] [c000000000121cac] .kernel_text_address+0x18c/0x1c0
  [c000000625c08c50] [c000000000061960] .prepare_ftrace_return+0x50/0x130
  [c000000625c08cf0] [c000000000061b10] .ftrace_graph_caller+0x14/0x34
  [c000000625c08d60] [c000000000121b40] .kernel_text_address+0x20/0x1c0
  [c000000625c08df0] [c000000000061960] .prepare_ftrace_return+0x50/0x130
  ...
  [c000000625c0ab30] [c000000000061960] .prepare_ftrace_return+0x50/0x130
  [c000000625c0abd0] [c000000000061b10] .ftrace_graph_caller+0x14/0x34
  [c000000625c0ac40] [c000000000121b40] .kernel_text_address+0x20/0x1c0
  [c000000625c0acd0] [c000000000061960] .prepare_ftrace_return+0x50/0x130
  [c000000625c0ad70] [c000000000061b10] .ftrace_graph_caller+0x14/0x34
  [c000000625c0ade0] [c000000000121b40] .kernel_text_address+0x20/0x1c0
  Instruction dump:
  7c0802a6 fbc1fff0 fbe1fff8 f8010010 f821ff81 7c7e1b78 7c9f2378 60000000
  60000000 e95e0031 7faaf040 419e0028 <e92a0010> 7fa9f840 3d090001 7ebf4040
  ---[ end trace 0870d7d56d703ff4 ]---

This is because ftrace is using ppc_function_entry() for obtaining the
address of return_to_handler() in prepare_ftrace_return(). The call to
kernel_text_address() itself gets traced and we end up in a recursive
loop.

Reported-by: Chandan Rajendra <chandan at linux.vnet.ibm.com>
Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/code-patching.h | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h
index 5482928eea1b..abef812de7f8 100644
--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -83,16 +83,8 @@ static inline unsigned long ppc_function_entry(void *func)
 	 * On PPC64 ABIv1 the function pointer actually points to the
 	 * function's descriptor. The first entry in the descriptor is the
 	 * address of the function text.
-	 *
-	 * However, we may also receive pointer to an assembly symbol. To
-	 * detect that, we first check if the function pointer we receive
-	 * already points to kernel/module text and we only dereference it
-	 * if it doesn't.
 	 */
-	if (kernel_text_address((unsigned long)func))
-		return (unsigned long)func;
-	else
-		return ((func_descr_t *)func)->entry;
+	return ((func_descr_t *)func)->entry;
 #else
 	return (unsigned long)func;
 #endif
-- 
2.14.2