4.4-stable review patch. If anyone has any objections, please let me know.
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From: Max Filippov jcmvbkbc@gmail.com
commit 2958b66694e018c552be0b60521fec27e8d12988 upstream.
coprocessor_flush_all may be called from a context of a thread that is different from the thread being flushed. In that case contents of the cpenable special register may not match ti->cpenable of the target thread, resulting in unhandled coprocessor exception in the kernel context. Set cpenable special register to the ti->cpenable of the target register for the duration of the flush and restore it afterwards. This fixes the following crash caused by coprocessor register inspection in native gdb:
(gdb) p/x $w0 Illegal instruction in kernel: sig: 9 [#1] PREEMPT Call Trace: ___might_sleep+0x184/0x1a4 __might_sleep+0x41/0xac exit_signals+0x14/0x218 do_exit+0xc9/0x8b8 die+0x99/0xa0 do_illegal_instruction+0x18/0x6c common_exception+0x77/0x77 coprocessor_flush+0x16/0x3c arch_ptrace+0x46c/0x674 sys_ptrace+0x2ce/0x3b4 system_call+0x54/0x80 common_exception+0x77/0x77 note: gdb[100] exited with preempt_count 1 Killed
Cc: stable@vger.kernel.org Signed-off-by: Max Filippov jcmvbkbc@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/xtensa/kernel/process.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/arch/xtensa/kernel/process.c +++ b/arch/xtensa/kernel/process.c @@ -83,18 +83,21 @@ void coprocessor_release_all(struct thre
void coprocessor_flush_all(struct thread_info *ti) { - unsigned long cpenable; + unsigned long cpenable, old_cpenable; int i;
preempt_disable();
+ RSR_CPENABLE(old_cpenable); cpenable = ti->cpenable; + WSR_CPENABLE(cpenable);
for (i = 0; i < XCHAL_CP_MAX; i++) { if ((cpenable & 1) != 0 && coprocessor_owner[i] == ti) coprocessor_flush(ti, i); cpenable >>= 1; } + WSR_CPENABLE(old_cpenable);
preempt_enable(); }