[PATCH] powerpc/livepatch: Fix livepatch stack access

[Naveen N . Rao]

On 2017/09/20 03:49PM, Kamalesh Babulal wrote:
> While running stress test with livepatch module loaded, kernel
> bug was triggered.
> 
> cpu 0x5: Vector: 400 (Instruction Access) at [c0000000eb9d3b60]
>     pc: c0000000eb9d3e30
>     lr: c0000000eb9d3e30
>     sp: c0000000eb9d3de0
>    msr: 800000001280b033
>   current = 0xc0000000dbd38700
>   paca    = 0xc00000000fe01400   softe: 0        irq_happened: 0x01
>     pid   = 8618, comm = make
> Linux version 4.13.0+ (root at ubuntu) (gcc version 6.3.0 20170406 (Ubuntu 6.3.0-12ubuntu2)) #1 SMP Wed Sep 13 03:49:27 EDT 2017
> 
> 5:mon> t
> [c0000000eb9d3de0] c0000000eb9d3e30 (unreliable)
> [c0000000eb9d3e30] c000000000008ab4 hardware_interrupt_common+0x114/0x120
>  --- Exception: 501 (Hardware Interrupt) at c000000000053040 livepatch_handler+0x4c/0x74
> [c0000000eb9d4120] 0000000057ac6e9d (unreliable)
> [d0000000089d9f78] 2e0965747962382e
> SP (965747962342e09) is in userspace
> 
> When an interrupt is served in between the livepatch_handler execution,
> there are chances of the livepatch_stack/task task getting corrupted.
> 
>                     CPU 1
>                  =============
> Task A                          Interrupt Handler
> =========                       =================
> livepatch_handler:
>  mr r0, r1
>  ld r1, TI_livepatch_sp(r12)
>                                 hardware_interrupt_common
>                                 |_do_IRQ
>                                   |_ call_do_irq:
>                                         mflr r0
>                                         std  r0,16(r1)
>                                         stdu r1,THREAD_SIZE-STACK_FRAME_OVERHEAD(r4)
>                                             ...
> lis r2, STACK_END_MAGIC at h
> ori r2, r2, STACK_END_MAGIC at l
> ld  r12, -8(r1)      <- livepatch stack is corrupted.
> 
> Fix the corruption by using r11 register for livepatch stack manipulation,
> instead of shuffling task stack and livepatch stack into r1 register.
> Using r11 register also avoids disabling/enabling irq's while setting
> up the livepatch stack.
> 
> Signed-off-by: Kamalesh Babulal <kamalesh at linux.vnet.ibm.com>
> Cc: Balbir Singh <bsingharora at gmail.com>
> Cc: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
> Cc: linuxppc-dev at lists.ozlabs.org
> ---
>  arch/powerpc/kernel/trace/ftrace_64_mprofile.S | 45 +++++++++-----------------
>  1 file changed, 15 insertions(+), 30 deletions(-)

Reviewed-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>


- Naveen