From 854236363370995a609a10b03e35fd3dc5e9e4a1 Mon Sep 17 00:00:00 2001 From: James Hogan Date: Thu, 29 Jun 2017 15:05:04 +0100 Subject: [PATCH] MIPS: Avoid accidental raw backtrace Since commit 81a76d7119f6 ("MIPS: Avoid using unwind_stack() with usermode") show_backtrace() invokes the raw backtracer when cp0_status & ST0_KSU indicates user mode to fix issues on EVA kernels where user and kernel address spaces overlap. However this is used by show_stack() which creates its own pt_regs on the stack and leaves cp0_status uninitialised in most of the code paths. This results in the non deterministic use of the raw back tracer depending on the previous stack content. show_stack() deals exclusively with kernel mode stacks anyway, so explicitly initialise regs.cp0_status to KSU_KERNEL (i.e. 0) to ensure we get a useful backtrace. Fixes: 81a76d7119f6 ("MIPS: Avoid using unwind_stack() with usermode") Signed-off-by: James Hogan Cc: linux-mips@linux-mips.org Cc: # 3.15+ Patchwork: https://patchwork.linux-mips.org/patch/16656/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/traps.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/mips/kernel/traps.c b/arch/mips/kernel/traps.c index 9681b5877140..38dfa27730ff 100644 --- a/arch/mips/kernel/traps.c +++ b/arch/mips/kernel/traps.c @@ -201,6 +201,8 @@ void show_stack(struct task_struct *task, unsigned long *sp) { struct pt_regs regs; mm_segment_t old_fs = get_fs(); + + regs.cp0_status = KSU_KERNEL; if (sp) { regs.regs[29] = (unsigned long)sp; regs.regs[31] = 0; -- 2.25.1