Commit f7d3d40e authored by James Hogan's avatar James Hogan Committed by Greg Kroah-Hartman

MIPS: Avoid accidental raw backtrace

commit 85423636 upstream.

Since commit 81a76d71 ("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: 81a76d71 ("MIPS: Avoid using unwind_stack() with usermode")
Signed-off-by: default avatarJames Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16656/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 3d4ac49a
...@@ -199,6 +199,8 @@ void show_stack(struct task_struct *task, unsigned long *sp) ...@@ -199,6 +199,8 @@ void show_stack(struct task_struct *task, unsigned long *sp)
{ {
struct pt_regs regs; struct pt_regs regs;
mm_segment_t old_fs = get_fs(); mm_segment_t old_fs = get_fs();
regs.cp0_status = KSU_KERNEL;
if (sp) { if (sp) {
regs.regs[29] = (unsigned long)sp; regs.regs[29] = (unsigned long)sp;
regs.regs[31] = 0; regs.regs[31] = 0;
......
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